Trascrizione
00:01:190Jacopo Vivian: Okay, so let's go back to the last slide.
00:14:260Jacopo Vivian: Yes, I think we stopped here.
00:20:500Jacopo Vivian: Don't remember.
00:24:820Jacopo Vivian: Yes.
00:55:980Jacopo Vivian: okay, yes.
00:57:500Jacopo Vivian: So I think we stopped here last time. Right, that was the last slide.
01:07:280Jacopo Vivian: So let's
01:10:710Jacopo Vivian: Let's recall the the concept of the slide that we I I told you, basically, that in
01:20:320Jacopo Vivian: traditional heat pumps the 1st heat pumps they were. They were on off heat pumps, and
01:28:10Jacopo Vivian: also, both in inverter driven heat pumps and on off heat pumps.
01:34:440Jacopo Vivian: The heat capacity, which means the maximum thermal power that the heat pump can deliver for certain conditions
01:44:790Jacopo Vivian: depends on the air source temperature and on the
01:54:268Jacopo Vivian: supply temperature to the system.
01:57:230Jacopo Vivian: Okay?
01:59:540Jacopo Vivian: So when we have inverter driven heat pumps, what are variable speed heat pumps, what does it change
02:10:130Jacopo Vivian: it? We can change the the frequency that supplies the compressor.
02:17:990Jacopo Vivian: That will, of course, reduce the circulating flow rate of refrigerant in the heat pump cycle. Okay?
02:30:760Jacopo Vivian: So by reducing it, we, we achieved this goal of reducing the thermal power.
02:40:20Jacopo Vivian: So always remember that for a given air source stamp
02:46:460Jacopo Vivian: outdoor air temperature and water supply temperature, we have
02:52:540Jacopo Vivian: a maximum heat that can be delivered. This maximum heat will be delivered at nominal frequency.
03:01:20Jacopo Vivian: It means, if the maximum frequency is 50 Hertz.
03:08:490Jacopo Vivian: When the compressor is supplied at 50 hertz, it will deliver that maximum capacity.
03:16:820Jacopo Vivian: If the supply temperature to the system is constant and the air temperature outdoor
03:28:700Jacopo Vivian: changes and decreases because it's colder.
03:32:600Jacopo Vivian: What will happen if we don't change the frequency.
03:38:770Jacopo Vivian: the thermal output will be lower.
03:41:780Jacopo Vivian: Okay, this is this is exactly what this green line is showing.
03:49:400Jacopo Vivian: Okay? So another way to reduce the thermal to change the thermal output is to work on the
04:02:220Jacopo Vivian: weather on the sorry on the supply temperature on the water supply temperature.
04:09:240Jacopo Vivian: But this is mainly done to achieve a higher cop.
04:15:60Jacopo Vivian: Okay? So basically, what I'm telling you is that in order to reduce the
04:23:50Jacopo Vivian: thermal output of the heat pump.
04:26:90Jacopo Vivian: we, the controller, normally regulates the frequency that supplies the compressor.
04:33:110Jacopo Vivian: Okay, and with the pid control or something like that.
04:40:180Jacopo Vivian: Okay, we have seen the pad control or
04:47:880Jacopo Vivian: and if we, if we need to make the average performance of the heat pump better, meaning that we want to reduce the electricity consumption over the year.
05:01:890Jacopo Vivian: Then we act with the so-called weather compensation curve.
05:09:310Jacopo Vivian: which means that the supply temperature is decreased when the outdoor temperature increases, but the remember that the
05:25:490Jacopo Vivian: if we reduce the the supply temperature.
05:29:220Jacopo Vivian: we are also reducing the delta t between heatsink and heat source.
05:34:600Jacopo Vivian: Okay?
05:35:650Jacopo Vivian: So we are also at the same time getting a higher thermal output.
05:44:970Jacopo Vivian: Okay, so we work at partial load.
05:48:410Jacopo Vivian: We always work at partial load with heat pumps all over the year.
05:53:440Jacopo Vivian: Okay, we when they are switched on, they work. They can work at the full load, or
06:04:460Jacopo Vivian: I don't know in the order of half an hour.
06:09:830Jacopo Vivian: and then they will for sure reduce their thermal output by frequency regulation.
06:21:260Jacopo Vivian: So this is the basic concept of this slide.
06:27:930Jacopo Vivian: Another important thing about heat pumps that is different from, and particularly air to water heat pumps
06:38:770Jacopo Vivian: is that when the outsider out outdoor air is cooled.
06:45:130Jacopo Vivian: Water vapor can condense on the evaporator. If the surface of the evaporator is cold enough, why? Because
07:01:220Jacopo Vivian: you, basically, you know that the water vapor moisture is one component of the air, but the
07:12:501Jacopo Vivian: below a certain temperature it will condense, and therefore we.
07:21:530Jacopo Vivian: We reach this this condition that is called the dew Point temperature.
07:26:420Jacopo Vivian: Okay, why is this a problem? Because if it condense and it freezes.
07:34:710Jacopo Vivian: Okay?
07:38:130Jacopo Vivian: There is an additional thermal resistance
07:42:750Jacopo Vivian: between the air, which is our heat source and the refrigerant.
07:50:650Jacopo Vivian: Okay, it means that our evaporator is not
07:56:550Jacopo Vivian: working properly because it is not able to provide the necessary
08:04:800Jacopo Vivian: heat to the refrigerant to exchange.
08:08:740Jacopo Vivian: They heat well enough with the refrigerant.
08:12:700Jacopo Vivian: Okay, therefore, frost is something frost on the evaporator.
08:19:940Jacopo Vivian: Okay, frost is the frozen
08:26:90Jacopo Vivian: moisture.
08:27:310Jacopo Vivian: Okay, is something that we want to avoid in order to
08:35:500Jacopo Vivian: improve the performance of the heat pump over the year, and particularly when temperatures are more or less.
08:46:870Jacopo Vivian: 5 Celsius degrees. Okay, this is the
08:51:490Jacopo Vivian: condition where we have more, where we more frequently have a moisture that freezes on the evaporator.
09:01:350Jacopo Vivian: This is how it looks like in the worst condition. Okay, you have a
09:10:490Jacopo Vivian: okay, maybe this is more realistic, the one on the on the right.
09:18:770Jacopo Vivian: So what what are the strategies to avoid the this situation to defrost?
09:29:130Jacopo Vivian: So there are defrosting cycles which are typically done by inverting the direction of the heat exchange.
09:40:330Jacopo Vivian: so the air will be the heat sink like in summer.
09:45:550Jacopo Vivian: and the heating system will be the heat source great.
09:50:710Jacopo Vivian: That means we are removing heat from the building when outside it is cold.
09:59:410Jacopo Vivian: So.
10:00:450Jacopo Vivian: 1st of all, we have a reduction in performance, because this is not the objective of of the heat pump.
10:09:540Jacopo Vivian: and, secondly, we might have discomfort.
10:13:990Jacopo Vivian: So fortunately this, in order to defrost the evaporator.
10:21:340Jacopo Vivian: we don't need to spend a lot of time. Few minutes are enough normally.
10:27:320Jacopo Vivian: because you defrost the evaporator as soon as the frost
10:33:140Jacopo Vivian: will appear. You don't defrost the evaporator when it's like this. Okay.
10:39:20Jacopo Vivian: you defrost when it's like this.
10:42:00Jacopo Vivian: So few minutes of water coming into the evaporator at the 2530 degrees. Okay.
10:54:400Jacopo Vivian: are enough to remove all the frost.
10:59:510Jacopo Vivian: Other possible strategies are to work with the electrical resistances.
11:05:980Jacopo Vivian: but in that also, in that case we have an avoidable electrical consumption
11:14:690Jacopo Vivian: that worsens the performance of the machine.
11:20:410Jacopo Vivian: And so what we?
11:23:80Jacopo Vivian: This is a in a heat pump that we use for some experiments. You can see that we have a
11:33:90Jacopo Vivian: okay, the see?
11:40:640Jacopo Vivian: Okay, this is the outdoor temperature.
11:43:570Jacopo Vivian: Okay? You see, in the that day that was January, we had the an outdoor temperature around 0 degrees.
11:55:650Jacopo Vivian: Okay, so below 0 during the night
11:59:350Jacopo Vivian: and higher than 0 during the day.
12:03:760Jacopo Vivian: and you can see that the
12:06:840Jacopo Vivian: here we have the red line is the thermal output delivered by the heat pump.
12:15:660Jacopo Vivian: The green line is the electrical consumption of the heat pump and the black line
12:26:580Jacopo Vivian: was the power delivered by the funk oil.
12:30:700Jacopo Vivian: Okay, thermal power.
12:34:850Jacopo Vivian: So here you can see that in this moment something strange. Of course
12:46:60Jacopo Vivian: we are not delivering it to the building.
12:49:450Jacopo Vivian: but we have a negative thermal power.
12:53:460Jacopo Vivian: This is why? Because we are defrosting.
12:56:820Jacopo Vivian: In this moment a sensor in the evaporator tells the heat pump that it is time to defrost.
13:04:520Jacopo Vivian: So the
13:06:650Jacopo Vivian: the cycle is inverted, and, as you can see, the duration in this car in this case was,
13:15:360Jacopo Vivian: okay, it is not easily you.
13:18:630Jacopo Vivian: It is not easy to to get it.
13:21:990Jacopo Vivian: but it is in the order of 30 min. And this was one of the coldest days of the year.
13:29:470Jacopo Vivian: Okay.
13:34:180Jacopo Vivian: So
13:46:710Jacopo Vivian: this is a okay. I I just found it a few minutes before the lecture, so don't
13:55:250Jacopo Vivian: look too much at the numbers. But I just want to show you our point, sir.
14:02:275Jacopo Vivian: How thermal power is distributed as a function of the outer temperature.
14:10:370Jacopo Vivian: as you can see. Okay, this is just the
14:14:200Jacopo Vivian: a very small range around 3 Kelvin on the x-axis.
14:20:190Jacopo Vivian: But basically we have
14:23:172Jacopo Vivian: this trend all over the year, which means we are delivering more power when it's warmer.
14:30:630Jacopo Vivian: Okay, that's why we want to use the
14:36:610Jacopo Vivian: Freak, the the inverter to modulate the compressor speed.
14:45:960Jacopo Vivian: Okay, that's it or heat pumps.
14:54:30Jacopo Vivian: And now I want to
15:01:780Jacopo Vivian: need to start the next presentation,
15:08:540Jacopo Vivian: you should have it already on moodle
15:49:580Jacopo Vivian: okay, now, I'm sharing the screen again.
15:57:840Jacopo Vivian: Okay.
16:02:130Jacopo Vivian: so as you know, we, we started from the building envelope and we
16:10:770Jacopo Vivian: went back to the generation systems.
16:14:790Jacopo Vivian: But basically in the reality, we have the heat generation as the first.st component. Okay?
16:26:360Jacopo Vivian: And then we have a distribution system and then emission system
16:31:370Jacopo Vivian: among the generation systems. We don't only have heat pumps. But traditionally we have fossil fuel boilers.
16:40:480Jacopo Vivian: When in Italy at least, the most common fossil fuel is natural gas. Okay?
16:49:870Jacopo Vivian: And for cooling. We have chillers in both cases
16:57:190Jacopo Vivian: both of chillers and heat pumps.
17:00:750Jacopo Vivian: The main sources and sinks are either the air or the ground depending on where we extract the heat, and where we reject the heat.
17:14:260Jacopo Vivian: you know by
17:19:800Jacopo Vivian: By previous lectures, that the and you can imagine that the heat demand is increasing
17:27:540Jacopo Vivian: with the by by going towards the design conditions. So towards the coldest temperature situation and the
17:41:90Jacopo Vivian: regarding the emission system, you know, for example, for a radiator. But in general all the emission system
17:51:380Jacopo Vivian: have a thermal power that depends on the temperature of the water in the
17:58:530Jacopo Vivian: emission system itself, in the heat emitter.
18:02:50Jacopo Vivian: So the low is this one for the radiator. Okay.
18:07:910Jacopo Vivian: a constant multiplied by the delta T between the air
18:13:850Jacopo Vivian: and the sorry between the average water temperature in the radiator and the air power, and
18:22:200Jacopo Vivian: where N is an exponent that depends on the geometry and the material of the radiator.
18:31:250Jacopo Vivian: So basically, you have this
18:37:810Jacopo Vivian: increase in the thermal output with the water supply temperature.
18:44:30Jacopo Vivian: So this is why we usually have these weather compensation curves that are
18:52:70Jacopo Vivian: inside that are implemented inside the controllers of generation systems.
18:57:920Jacopo Vivian: Because you want to deliver more thermal power to the indoor environment when outside is colder.
19:06:200Jacopo Vivian: And this is a a good choice, not only to
19:11:934Jacopo Vivian: warm up more when outside is colder, but also to save energy during the year.
19:19:930Jacopo Vivian: because the lower the supply temperature
19:24:440Jacopo Vivian: the higher, the efficiency of the generation system
19:28:780Jacopo Vivian: being it a heat pump or a gas boiler, you have some improvement in both cases.
19:40:360Jacopo Vivian: Let's talk a bit about fossil fuel boilers
19:46:450Jacopo Vivian: with most typical case, I told you, is natural gas.
19:52:370Jacopo Vivian: Basically, we have a
19:57:10Jacopo Vivian: we have the pipe connections. Okay, we have the combustion chambers chamber and a heat exchanger
20:07:440Jacopo Vivian: where the water is warm up.
20:12:530Jacopo Vivian: and then the com, the combustion products.
20:16:710Jacopo Vivian: So the fumes are, or the
20:20:740Jacopo Vivian: they are also called exhaust gas. They are
20:25:353Jacopo Vivian: blown out of the out of the boiler. Okay?
20:30:230Jacopo Vivian: So with this configuration, that is the typical gas boiler.
20:36:600Jacopo Vivian: We have some losses in the conversion of energy between chemical energy. Okay, the heating value of the fuel
20:48:150Jacopo Vivian: to hit the these losses are combustion losses. If the combustion is incomplete.
20:57:540Jacopo Vivian: losses in the envelope, meaning that the envelope of the gas boiler
21:05:720Jacopo Vivian: is at the surface temperature of the gas boiler, if you touch, it
21:11:550Jacopo Vivian: is at a higher temperature than the air.
21:15:580Jacopo Vivian: and this means that the boiler is releasing heated to their surroundings.
21:23:850Jacopo Vivian: If the boiler is not in the heated environment. This is a loss.
21:29:980Jacopo Vivian: Okay?
21:33:310Jacopo Vivian: And then you have chimney losses because they exhaust the gas
21:38:770Jacopo Vivian: has an enthalpy content that is
21:45:650Jacopo Vivian: blown away. So it is going out of our control volume when we.
21:51:610Jacopo Vivian: when we assess the energy balance of the gas boiler, and therefore it is a further loss.
21:58:410Jacopo Vivian: Okay, how have boilers evolved over time?
22:05:540Jacopo Vivian: So basically, there have been a a limited set of improvement.
22:14:990Jacopo Vivian: first, st increasing the insulation of the envelope to reduce envelope losses.
22:21:640Jacopo Vivian: Second, we have the option to control the supply temperature.
22:29:50Jacopo Vivian: This is what I said before.
22:31:923Jacopo Vivian: So that we can reduce the average temperature of the heating system when outside is warmer.
22:40:690Jacopo Vivian: and then on the technology side, we have the use of premix burners.
22:47:180Jacopo Vivian: So burner is the most important component of the gas boiler and the Premix burner has
22:55:860Jacopo Vivian: the advantage of improving the combustion efficiency.
23:01:850Jacopo Vivian: How? By mixing the air that is used for the combustion, which is the oxygen carrier. Okay? And
23:12:920Jacopo Vivian: with the fuel. That is also a gas, because natural gas and air are 2 gases.
23:21:780Jacopo Vivian: So they are mixed before the flame is, oh, is reached.
23:30:10Jacopo Vivian: So this allows a better combustion quality, because the
23:37:130Jacopo Vivian: basically the hydrocarbon is closer to the oxygen. Okay? And the mixture of the gases improves the quality of the oxidation process.
23:50:980Jacopo Vivian: So the in practical engineering terms. This means that we can achieve the same
24:00:650Jacopo Vivian: efficiency, but with lower excess rate. You know that to have a better combustion in general we work with the excess air.
24:11:830Jacopo Vivian: meaning that if you do the chemical balance, the stoichiometric balance of the reaction.
24:19:340Jacopo Vivian: you get a certain number of kilograms of oxygen per kilogram of fuel.
24:29:00Jacopo Vivian: but in the reality you always, which means also higher
24:36:40Jacopo Vivian: kilograms of air per kilogram of fuel.
24:40:10Jacopo Vivian: Okay?
24:41:160Jacopo Vivian: So if you have a certain flow rate of a natural gas coming into the gas chamber.
24:49:340Jacopo Vivian: into the sorry into the gas boiler.
24:54:20Jacopo Vivian: Then you know by the stoichiometric balance what is the theoretical
25:00:750Jacopo Vivian: mass flow rate of air that should come
25:04:690Jacopo Vivian: by the by, the reaction you should know the the mass flow rate of oxygen. But we know that in air we have a 23% of
25:19:700Jacopo Vivian: oxygen. So in terms of mass.
25:23:750Jacopo Vivian: So we get the mass flow rate of air that should come into the gas boiler.
25:29:590Jacopo Vivian: In the reality we always work with a higher mass flow rate of air. Why? Because we want to reach a higher mix
25:38:810Jacopo Vivian: in the combustion chamber between oxygen and natural gas.
25:45:590Jacopo Vivian: So with the premix burners, we improve this aspect.
25:53:910Jacopo Vivian: And we can reduce the excess air.
25:57:690Jacopo Vivian: Okay.
25:59:680Jacopo Vivian: so instead of working with 40 to 80% excess air, we work with the 15 to 20%.
26:11:890Jacopo Vivian: This is how we we are
26:20:00Jacopo Vivian: from, let's say, from a geometrical point of view.
26:24:888Jacopo Vivian: You can see 2 types of burners.
26:29:680Jacopo Vivian: Okay?
26:30:820Jacopo Vivian: And here you have the Premix burner, where
26:35:940Jacopo Vivian: we have flue, gas, fuel gas. Sorry here.
26:40:530Jacopo Vivian: and we have an air gas mixture that is sent here below the below the injector.
26:55:370Jacopo Vivian: So before the flame, okay, be before the ports.
27:05:620Jacopo Vivian: Okay?
27:06:960Jacopo Vivian: So another another improvement in in gas boiler technology
27:18:490Jacopo Vivian: was to use the use of modular boilers?
27:23:220Jacopo Vivian: Okay?
27:25:320Jacopo Vivian: They are very
27:29:350Jacopo Vivian: They are very practical because they can deliver a part of the heat load.
27:37:282Jacopo Vivian: They can work easily even when the other modules are off
27:43:180Jacopo Vivian: and they can save energy compared to having a single centralized boiler.
27:51:340Jacopo Vivian: Okay?
27:59:50Jacopo Vivian: And the main improvement has been the introduction of condensing gas boilers we have. I have already
28:09:500Jacopo Vivian: told before that one of the losses of gas boilers is too many losses.
28:18:650Jacopo Vivian: so the exhaust gas that is expelled from the boiler
28:24:800Jacopo Vivian: is has a certain enthalpy content
28:28:600Jacopo Vivian: that is going out of our component.
28:33:840Jacopo Vivian: So it is accounting as a loss.
28:36:970Jacopo Vivian: But inside this gossip there is again water.
28:45:740Jacopo Vivian: Okay.
28:47:130Jacopo Vivian: If you think about the the reaction of oxy.
28:53:100Jacopo Vivian: the combustion reaction, you have a hydrocarbon plus oxygen
28:59:730Jacopo Vivian: which leads to Co 2 plus water.
29:04:400Jacopo Vivian: So we have a certain water content inside the exhaust gas.
29:12:20Jacopo Vivian: If you are able to recover energy from this water, you have it recover part of this
29:22:490Jacopo Vivian: enthalpy loss of the exhaust gases.
29:26:250Jacopo Vivian: And this is exactly what happens in the condensing gas boilers.
29:31:660Jacopo Vivian: So we have an additional heat exchanger. You see it here that will allow that will make
29:41:340Jacopo Vivian: the water content in the exhaust gas condenser.
29:47:180Jacopo Vivian: Okay?
29:49:210Jacopo Vivian: And therefore we recover the latent heat of vaporization of water in the exhaust gases.
29:59:20Jacopo Vivian: Of course this can happen again only if we have a cold enough surface.
30:06:760Jacopo Vivian: Okay.
30:07:850Jacopo Vivian: so here in this graph. You see what is the dew Point temperature, so the temperature of the surface that will make the water condense
30:18:350Jacopo Vivian: as a function of the excess air.
30:22:520Jacopo Vivian: If we work with the 20% air access, you can see here, the dew point temperature
30:33:160Jacopo Vivian: in the exhaust gases is around 55 degrees exactly 55.6.
30:43:360Jacopo Vivian: So this means that in the return the the return temperature of the water from the
30:54:270Jacopo Vivian: system from the heating system should be lower than 55.6,
31:01:630Jacopo Vivian: otherwise there is no condensation, because the surface of the heat exchanger
31:07:580Jacopo Vivian: is not cold enough to let the water condense on the heat exchanger surface.
31:13:840Jacopo Vivian: So this means that if we have a condensing gas boiler and we operate at 80 60,
31:23:740Jacopo Vivian: it is completely useless, because we are not recovering the water, content
31:31:110Jacopo Vivian: the heat content of the water inside the flue gases.
31:35:940Jacopo Vivian: Okay.
31:37:250Jacopo Vivian: So remember that the weather compensation curve that we have seen before
31:42:520Jacopo Vivian: is not only useful for heat pumps, because they
31:46:250Jacopo Vivian: deliver heat at the lower supply temperature, and therefore they are
31:54:450Jacopo Vivian: working with lower Delta T between the heat source and the heat sink.
31:59:430Jacopo Vivian: They are also useful for condensing gas boilers, because the lower the return temperature, of course, the lower the supply temperature for the same load, the lower the return temperature
32:11:540Jacopo Vivian: and the lower the return temperature the higher the amount of water
32:18:940Jacopo Vivian: that will condense in the gas boiler and will not leave
32:24:330Jacopo Vivian: through the chimney in the form of wet exhaust gas.
32:31:150Jacopo Vivian: Okay of water.
32:36:533Jacopo Vivian: Okay. So if we look at the the energy balance of the
32:45:900Jacopo Vivian: of the condensing gas boiler. We can see that if we consider the lower heating value.
32:54:220Jacopo Vivian: Okay?
32:55:150Jacopo Vivian: So without considering the energy content of the water in the flue gases.
33:04:790Jacopo Vivian: Remember that the lower hitting value
33:07:630Jacopo Vivian: does not consider the latent heat of vaporization of water in the flue gases and the higher heating value
33:16:70Jacopo Vivian: is considering it.
33:18:260Jacopo Vivian: Okay, I guess you have seen this lot of times.
33:22:930Jacopo Vivian: So we have a number of losses in the gas boiler.
33:27:360Jacopo Vivian: We have the heat losses of the flue gas.
33:32:40Jacopo Vivian: Of course, if the temperature of the flue gas is 120 degrees.
33:39:660Jacopo Vivian: this is a heat loss. Okay? Because
33:44:320Jacopo Vivian: we have a flow rate of gas that is not eating our house.
33:51:150Jacopo Vivian: and then we have the sensible heat losses through the envelope of the gas boiler.
33:58:70Jacopo Vivian: This is what I told before. If you touch the surface of the gas boiler, it is hot.
34:05:990Jacopo Vivian: so it is radiating heat to the environment.
34:09:770Jacopo Vivian: And this is a sensible heat loss through the envelope.
34:14:989Jacopo Vivian: Then we have heat losses from the chimney. Okay, again,
34:26:330Jacopo Vivian: and all the rest is going to the heating system.
34:30:139Jacopo Vivian: So this is our, this is our
34:36:270Jacopo Vivian: the effect we want to achieve.
34:42:159Jacopo Vivian: And so if we, if we consider the lower heating value.
34:49:760Jacopo Vivian: the heat that we supply to the system, provided that it is working at the temperature, that is.
34:59:200Jacopo Vivian: with an average return temperature lower than 55 degrees. Okay, we can deliver
35:08:270Jacopo Vivian: in this example 100 and maximum 106%
35:16:570Jacopo Vivian: of the energy that we would account with a lower heating value.
35:21:240Jacopo Vivian: Okay.
35:25:750Jacopo Vivian: of course, we are not always able to recover the latent heat of vaporization in the flue gases, so we also have this lost
35:36:610Jacopo Vivian: this loss. But this loss is accounted only if we consider the higher hitting value of the natural gas.
35:48:330Jacopo Vivian: otherwise, everything that whatever we we can condense is just a positive
35:59:800Jacopo Vivian: contribution to the to the efficiency.
36:03:100Jacopo Vivian: If we consider also the Latin heat of upperization meaning, we consider the higher heating value at the denominator.
36:12:370Jacopo Vivian: then we have a loss, because we cannot always condense all the water vapor.
36:22:520Jacopo Vivian: So this is how we typically assess the efficiency of gas boilers. And since we
36:32:440Jacopo Vivian: usually refer to the to the lower heating value of the natural gas.
36:38:750Jacopo Vivian: or whatever fuel we have, we have a normally.
36:43:10Jacopo Vivian: an efficiency. If we are working with the condensing gas boiler that can be higher than 100%.
36:50:950Jacopo Vivian: Okay, how much higher, again, that
36:56:380Jacopo Vivian: not higher than 106%, because we have
37:02:910Jacopo Vivian: a maximum amount of water in the flue gases. That depends on the combustion, on the reaction.
37:09:930Jacopo Vivian: and that mass of water or flow rate of water has a certain latent heat of vaporization.
37:18:580Jacopo Vivian: So we cannot recover more than that.
37:21:680Jacopo Vivian: Okay, without condensation. Our efficiency is lower than 96%.
37:31:250Jacopo Vivian: So reasonable values are of condensing gas boilers
37:38:730Jacopo Vivian: without condensation, we can have a
37:42:530Jacopo Vivian: 95%, 92 to 95%.
37:48:460Jacopo Vivian: And with condensation, we can have, you know.
37:53:50Jacopo Vivian: 101% to 105%, 103% is a reasonable value.
38:00:620Jacopo Vivian: of course, always refer to the lower heating value of the natural gas.
38:09:210Jacopo Vivian: We also have other options that are quite used in the north of it.
38:15:450Jacopo Vivian: north of Italy, especially in regions where we have forests like typically in Italy, they are mountainous regions, regions with mountains
38:29:680Jacopo Vivian: that are wood chips, boilers, or stoves
38:35:838Jacopo Vivian: woodchip boilers are typical of
38:40:50Jacopo Vivian: district heating systems of mounting regions. So systems where the heating station supplies more than one building.
38:49:750Jacopo Vivian: because it is a convenient fossil fuel. Also.
38:55:560Jacopo Vivian: on the economical side. We don't need to buy natural gas that is delivered from abroad.
39:05:790Jacopo Vivian: But we used a local fuels.
39:12:900Jacopo Vivian: That is also renewable from the energy point of view.
39:17:620Jacopo Vivian: Okay, from the environmental point of view. Bms is a renewable energy source.
39:25:260Jacopo Vivian: Why? Because the biomass meaning trees that we can cut to. Then you then be used by boilers
39:34:680Jacopo Vivian: in order to grow absorbs Co. 2.
39:40:730Jacopo Vivian: So during this life cycle, the Co. 2 that is emitted during combustion
39:50:90Jacopo Vivian: is compensated by the Co. 2 that that tree has absorbed during the growing process.
39:58:700Jacopo Vivian: Okay, so this is why it is considered a sustainable way to deliver heat.
40:08:510Jacopo Vivian: It is also incentivized. Okay.
40:13:310Jacopo Vivian: but I invite you to and also it is quite used in residential applications in the form of
40:25:525Jacopo Vivian: wood locks or pellet. Okay, pellet or cipato in Italian.
40:32:360Jacopo Vivian: depending on the size of the wooden pieces.
40:37:360Jacopo Vivian: and here you can see the distribution of
40:42:270Jacopo Vivian: wood combustion technologies in Italy. Over the years.
40:46:860Jacopo Vivian: You can see there is a reduction in the last 20 years of fireplaces. Okay, classical community they are
40:57:820Jacopo Vivian: reducing over the year.
41:01:125Jacopo Vivian: Stoves, and we have an increase in pallet and other type of stoves like those in the pictures.
41:13:980Jacopo Vivian: Okay?
41:16:220Jacopo Vivian: So of course, open fireplaces are also dangerous, because we have
41:25:500Jacopo Vivian: open fire in the in the house. I don't think it is allowed anymore. You should
41:33:653Jacopo Vivian: confine the combustion inside the closed chamber, and therefore you have a
41:40:120Jacopo Vivian: I think this. This is in the
41:42:800Jacopo Vivian: A row of advanced fireplaces. Basically, it is
41:48:503Jacopo Vivian: fireplace, which is closed with a glass box. Okay?
41:57:720Jacopo Vivian: And the this is a
42:03:380Jacopo Vivian: This is an example of,
42:08:790Jacopo Vivian: How it is working. Basically, you have a container.
42:12:940Jacopo Vivian: and then the the palette or the
42:18:120Jacopo Vivian: logs are sent to the, to the burner with a certain
42:25:650Jacopo Vivian: exchange in order to leave the combustion chamber work at the always
42:34:120Jacopo Vivian: as long as possible at the nominal load. Okay.
42:39:880Jacopo Vivian: in solid. The combustion of solids is more difficult to achieve.
42:46:830Jacopo Vivian: A let's say, a good combustion compared to liquid or gas viewers.
42:56:640Jacopo Vivian: So this is the difficulty on the technological side
43:01:900Jacopo Vivian: to always fuel, to always supply the wood in the
43:09:340Jacopo Vivian: correct amount, depending on how also at at partial load operation.
43:20:710Jacopo Vivian: So in this case you want to have as much as possible design conditions in the
43:30:500Jacopo Vivian: in the stove, in the boiler. Okay?
43:36:830Jacopo Vivian: And you know that although it is considered, it is actually a renewable energy source. It has also
43:46:10Jacopo Vivian: the combustion of wood has also an impact on human health, especially in regions like ours, where we have
43:57:180Jacopo Vivian: low air quality.
44:00:20Jacopo Vivian: Okay, and wood combustion is contributing to this low air quality. Okay?
44:09:80Jacopo Vivian: Because, of course, the pollutants, we should not only consider Co 2, because, Co. 2,
44:16:280Jacopo Vivian: we want to reduce it on a local on a global scale.
44:20:690Jacopo Vivian: But we should also consider the local effect of combustion like
44:26:430Jacopo Vivian: particulate emissions, particulate matter emission. That is a quite high for wood combustion compared to compared to gas combustion.
44:40:560Jacopo Vivian: Okay, of course, this is a
44:46:880Jacopo Vivian: science. I mean, this is. There is evidence of this. You can find technical reports saying this.
44:56:210Jacopo Vivian: but of course the lobby of the
45:00:230Jacopo Vivian: of the resellers of wooden stoves and those kind of technologies will deny the effect that
45:10:170Jacopo Vivian: of it. So always look at the
45:15:80Jacopo Vivian: credible sources. When you inform yourself about these matters.
45:22:640Jacopo Vivian: I think that's it from the gas, from the boilers about boilers.
45:31:70Jacopo Vivian: I want to spend a few words about the heat pumps again, because,
45:40:650Jacopo Vivian: we have also discussed last time about heat pumps, and
45:51:590Jacopo Vivian: I want to show you something.
46:05:300Jacopo Vivian: Here.
46:06:860Jacopo Vivian: i i i just make some simple calculations about the building
46:17:00Jacopo Vivian: with the 300 m² of heated surface.
46:21:860Jacopo Vivian: Okay, so I just put some realistic numbers here
46:29:62Jacopo Vivian: the air. The volume of heated air is around 900 cubic meters.
46:36:900Jacopo Vivian: And this is the
46:43:200Jacopo Vivian: Okay, then we have the
46:48:70Jacopo Vivian: air change rates in this building, sir, and we have some transmission losses.
46:56:260Jacopo Vivian: This is the thermal transmittance of walls, windows, and roof and their surface area okay to the outdoor air.
47:08:710Jacopo Vivian: So we reach it.
47:10:590Jacopo Vivian: Transmission losses equal to 183 watt per Kelvin
47:17:920Jacopo Vivian: and ventilation losses with the air change rate of 0 point 3 of around 90
47:25:770Jacopo Vivian: to Watt per Kelvin. So overall, we have these numbers
47:32:710Jacopo Vivian: 2,275 Watt per Kelvin
47:38:50Jacopo Vivian: of heat losses due to transmission and ventilation.
47:45:420Jacopo Vivian: Let's consider a building in our climate meaning 2,350 degree days.
47:55:910Jacopo Vivian: Okay of the heating season.
48:00:200Jacopo Vivian: So if you use those number, you get a heat demand over the heating season of
48:08:370Jacopo Vivian: 11,600 kilowatt hours thermal.
48:12:680Jacopo Vivian: Okay, if you divide by the heated surface, you have
48:19:160Jacopo Vivian: almost 39 kilowatt hour per
48:23:430Jacopo Vivian: square meter, which is more or less okay, because we have a well insulated walls. So it is realistic.
48:36:450Jacopo Vivian: now, I want to show you what happens if you want to supply such a building with the heat pump, and you want to size the heat pump.
48:48:850Jacopo Vivian: If you if you take the classical method, you multiply the you multiply the
49:06:870Jacopo Vivian: Hmm, you. You multiply the the vat per kelvin by the design temperature, difference
49:16:170Jacopo Vivian: between indoor air and outdoor air. So 20 minus minus 5 for our climate is 25,
49:23:730Jacopo Vivian: and you get the 8.4 kilowatt.
49:28:700Jacopo Vivian: But now I want to.
49:31:310Jacopo Vivian: I want you to for you, sir.
49:35:10Jacopo Vivian: on something else like what if we don't use this method to size the heat pump.
49:42:290Jacopo Vivian: but we consider that
49:47:00Jacopo Vivian: It should not match exactly the thermal power in a given moment.
49:53:930Jacopo Vivian: which is the moment of the year where you have minus 5.
49:58:300Jacopo Vivian: But you want to provide the right amount of energy during the coldest day of the year.
50:05:930Jacopo Vivian: Okay.
50:07:350Jacopo Vivian: So of course, we would need the simulation to do it. But I just replaced with some realistic numbers.
50:17:180Jacopo Vivian: So during the coldest day of the year, we have 22 degree days.
50:22:580Jacopo Vivian: So we have a heat demand during the coldest day of 109 kilowatt hours.
50:31:100Jacopo Vivian: Okay, so what is the thermal power that we need to
50:38:950Jacopo Vivian: choose to select the heat pump for this house if you choose the normal, the standard calculation with the 25 Kelvin difference
50:51:360Jacopo Vivian: and the and this method of the heat demand.
50:59:760Jacopo Vivian: Of course, it depends on the number of hours
51:04:220Jacopo Vivian: where the heat, where the system is on. If the system is on for
51:10:330Jacopo Vivian: 24 h, you should divide the heated demand of the coldest day by 24, if we
51:19:120Jacopo Vivian: assume that the
51:21:540Jacopo Vivian: we want to switch on the heat pump for a lower number of hours you can reduce.
51:29:440Jacopo Vivian: So I consider 18 h in one day.
51:34:370Jacopo Vivian: So we get this situation. If we consider the heat demand of the coldest day. During 18 HI achieve
51:46:650Jacopo Vivian: 6 kilowatt thermal output.
51:50:980Jacopo Vivian: If I consider the peak load with a traditional calculation method from a
51:57:330Jacopo Vivian: the standard I achieve 8.4.
52:02:360Jacopo Vivian: So I am reducing.
52:07:460Jacopo Vivian: I I assume that
52:13:370Jacopo Vivian: One of these methods is not is not the best.
52:18:420Jacopo Vivian: I mean, because if we have a difference of 40%, okay.
52:24:600Jacopo Vivian: so this is one observation that I want you to to make.
52:33:260Jacopo Vivian: The second thing is that we should consider how we deliver the heat.
52:40:340Jacopo Vivian: Do we have radiators? Do we have fun coils? Do we have a radiant floor.
52:46:210Jacopo Vivian: If you have a so-called wet, radiant floor.
52:50:10Jacopo Vivian: so not the dry systems that are put above the floor.
52:56:280Jacopo Vivian: but the ones that are with the pipes inside the screen inside the macedo. Okay?
53:04:500Jacopo Vivian: Then you should consider that this material.
53:10:760Jacopo Vivian: How? How does the radiant floor work?
53:13:620Jacopo Vivian: You have some pipes in the pavement. And you are warming up this script.
53:22:170Jacopo Vivian: Okay, you are warming up the layer of construction material around the 5.
53:30:690Jacopo Vivian: So let's look at this material.
53:34:420Jacopo Vivian: Okay, take it from the energy and buildings course.
53:39:260Jacopo Vivian: Here you have the thermal properties of discrete that is used in floor heating systems.
53:50:500Jacopo Vivian: So we have with. In this house we have a 300 m² of heated surface.
54:01:560Jacopo Vivian: So let's assume we have 210 m² of radiant floor.
54:10:60Jacopo Vivian: We have a thickness of the script of 5 cm. Okay, it is the thickness where the pipes are buried in the pavement
54:22:900Jacopo Vivian: so overall. If we multiply the surface by the thickness. We have the volume of screed
54:31:100Jacopo Vivian: which is surrounding our pipes. Of the radian floor.
54:35:200Jacopo Vivian: which is 10.5 cubic meters.
54:39:460Jacopo Vivian: This 10.5 cubic meters
54:42:550Jacopo Vivian: have a very high thermal capacity.
54:45:730Jacopo Vivian: meaning that due to the specific heat of this construction material.
54:51:930Jacopo Vivian: it takes a lot of time to warm up and to cool down this volume of screed.
55:01:410Jacopo Vivian: So how much heat can we store inside the building itself?
55:07:830Jacopo Vivian: It depends on how much we hit.
55:12:40Jacopo Vivian: we heat it. Okay? So if we bring the heat, this this layer of concrete
55:22:120Jacopo Vivian: from 20 to 25, it will take time for the heat to be then delivered to the building, so we can store that amount of heat.
55:34:840Jacopo Vivian: Then we switch off the generation system
55:38:310Jacopo Vivian: and the pavement will continue to deliver heat to the building because it has a high thermal inertia. Okay.
55:47:870Jacopo Vivian: so assume we overheat we. We give 5 Kelvin more today.
55:56:242Jacopo Vivian: To the pavement.
55:59:390Jacopo Vivian: Then we can store 13.5 kilowatt hours of thermal energy in the pavement.
56:06:510Jacopo Vivian: Okay, let's compare this value with what we can achieve achieve with a tank, a hot water tank.
56:19:800Jacopo Vivian: Okay, we take another tank of 300 liters, which means 0 point 3 cubic meters.
56:30:590Jacopo Vivian: With the specific heat of water.
56:33:100Jacopo Vivian: We get the thermal, the heat capacity.
56:36:280Jacopo Vivian: We assume that we again we heat up the tank before the load.
56:44:750Jacopo Vivian: and then the tank will deliver the heat to the building.
56:49:50Jacopo Vivian: In this case we are not constrained, because, of course, the pavement we can.
56:56:00Jacopo Vivian: You know that we have a maximum surface temperature
56:59:600Jacopo Vivian: in the pavement, so we cannot
57:02:730Jacopo Vivian: heat up the pavement to 40 degrees, because otherwise we will cause a local discount.
57:09:950Jacopo Vivian: But we can heat up more the water in the tank because we are not
57:16:260Jacopo Vivian: causing discomfort to the user. If we heat up the water in the tank right? Nothing happens. So in this case I use double the Delta. Ti use 10 kelvin.
57:29:20Jacopo Vivian: For example, we heat up the water in the tank from 50 to 60,
57:36:70Jacopo Vivian: and then after that the tank will deliver the
57:41:80Jacopo Vivian: energy to the radian system. In this case, then, we can store 3.4 kilowatt hour.
57:50:780Jacopo Vivian: You can see that this value is more or less, 4 times less than the heat that we can store in the pavement.
58:00:450Jacopo Vivian: Of course this is just a simplified method, but you need to know, what are
58:09:70Jacopo Vivian: you need to be familiar
58:11:30Jacopo Vivian: with the with the concept of having the building as an active component of the heating system. Okay.
58:21:150Jacopo Vivian: so in this case.
58:26:370Jacopo Vivian: it is reasonable to think that we can use to. That we can use the the floor heating system as a sort of thermal storage for the building.
58:37:300Jacopo Vivian: Okay?
58:38:900Jacopo Vivian: And this is useful because we have seen depending on how we size
58:46:950Jacopo Vivian: the building, the sort of the heat pump we have completely different values.
58:52:980Jacopo Vivian: So then, I just make some simple calculation to show how the
59:03:770Jacopo Vivian: heat pump size by with the 6.7 kilowatt.
59:09:610Jacopo Vivian: which is 10% more than what we get here
59:13:610Jacopo Vivian: is performing compared to a heat pump of 9.3 kilowatt.
59:20:960Jacopo Vivian: which is 10% more of the traditional sizing procedure.
59:27:910Jacopo Vivian: What I get is this, in the 1st case, the it takes it takes 6 h to
59:43:75Jacopo Vivian: to cool down the pavement
59:45:940Jacopo Vivian: from an average temperature of 29 degrees 2,
59:52:430Jacopo Vivian: an average temperature of 23,
59:56:280Jacopo Vivian: and then, if I switch on the heat pump.
00:00:620Jacopo Vivian: it will reach it will reach a new steady state value at 27 degrees.
00:08:650Jacopo Vivian: It means that we are not able to reach 29,
00:13:440Jacopo Vivian: but with 27 degrees in the pavement.
00:18:450Jacopo Vivian: We are delivering 6.7 kilowatt, which is the size of the heat pump. Okay?
00:27:860Jacopo Vivian: And we are not. And the thermal losses of the envelope in this situation.
00:35:580Jacopo Vivian: on average, during the 24 h are 4.5 kilowatt.
00:41:460Jacopo Vivian: So it means that even if we don't use the traditional sizing procedure for the heat pump
00:50:440Jacopo Vivian: in the coldest day of the year.
00:53:470Jacopo Vivian: We are able to provide the correct amount of heat to the building.
01:00:660Jacopo Vivian: Okay, because the thermal power delivered by the floor heating system is the same of the heat pump.
01:07:410Jacopo Vivian: and is higher than the heat losses of the envelope.
01:11:90Jacopo Vivian: Considering both transmission and ventilation losses.
01:17:620Jacopo Vivian: although we are not able to cover the peak load of 9 kilowatt.
01:24:10Jacopo Vivian: Okay?
01:26:760Jacopo Vivian: And you can see
01:28:650Jacopo Vivian: we don't take it doesn't take too much time to reach the steady state condition with the
01:35:680Jacopo Vivian: heat pump, that, according to the traditional method, it would be undersized.
01:41:440Jacopo Vivian: Okay, it takes from ours number 6 to more or less our number 12.
01:50:50Jacopo Vivian: So why am I? What happens? In the other case?
01:58:260Jacopo Vivian: It happens that the we reach the 29 degrees with 29 degrees we.
02:09:450Jacopo Vivian: the radian floor, is delivering 9.3 kilowatt.
02:13:890Jacopo Vivian: which is double the losses of the envelope.
02:20:210Jacopo Vivian: So what I what I what I'm telling you is that during the
02:28:120Jacopo Vivian: if you if you size the heat pump for the for its design peak loader like you do with a boiler.
02:35:890Jacopo Vivian: you are basically oversizing the heat pump from an energy point of view, because
02:41:660Jacopo Vivian: in this case, with the 9.3 kilowatt at a certain point.
02:48:00Jacopo Vivian: the heat pump will switch off.
02:50:850Jacopo Vivian: and this is the or will modulate will reduce the load.
02:55:340Jacopo Vivian: and this is the coldest day of the year.
02:57:880Jacopo Vivian: So imagine what happens during spring.
03:01:200Jacopo Vivian: this heat pump will on, will go on off continuously.
03:05:300Jacopo Vivian: Okay?
03:07:90Jacopo Vivian: So oh, heat pump, sir.
03:11:630Jacopo Vivian: are not like boilers. We cannot just switch on off because the continuous on off of the heat pump will make it work with the lower cop on average.
03:24:270Jacopo Vivian: and then you will have high
03:26:940Jacopo Vivian: electrical consumption, because the heat pump is going on and off.
03:32:570Jacopo Vivian: Second thing, why did I consider in both cases 10% more?
03:38:980Jacopo Vivian: Because I showed before that we have, especially when it's colder, we have the frost.
03:47:610Jacopo Vivian: So if we have the frosting exactly here, when we reach, when we need to deliver
03:56:580Jacopo Vivian: energy to the to the building during the startup.
04:01:110Jacopo Vivian: We need to have some excessive power excess power.
04:08:480Jacopo Vivian: because we are not continuously heating up here. We might have a defrosting cycle exactly here.
04:16:720Jacopo Vivian: and then we need to have more power to be faster to heat up the building. Okay, so
04:25:875Jacopo Vivian: for the report, which is what is of interest for you.
04:31:960Jacopo Vivian: What do you need to do?
04:34:865Jacopo Vivian: You need to? With this year? We don't have the sizing of the valve. Okay?
04:43:310Jacopo Vivian: Because I think it is more interesting for you to look at the heat pump car catalogs
04:49:390Jacopo Vivian: and to choose a heat pump that is suitable for your case.
04:53:980Jacopo Vivian: So I we don't require any.
05:01:770Jacopo Vivian: I mean, you are free to make calculations. Of course you are not required to do this calculation. Okay.
05:10:470Jacopo Vivian: you can, but you can make some thoughts about the heat pump you choose.
05:19:30Jacopo Vivian: based on what we have said in the last, in the last lecture, if you remember in the last lecture
05:26:560Jacopo Vivian: I showed a technical, the technical data of a heat pump.
05:31:610Jacopo Vivian: And I told you that in the data sheet of the heat pumps.
05:36:150Jacopo Vivian: We have the heat, capacity, and the cop in
05:43:470Jacopo Vivian: nominal conditions that are defined by the standard.
05:48:520Jacopo Vivian: And then I showed the that that you should adapter
05:55:450Jacopo Vivian: the heat capacity to the design condition.
05:59:630Jacopo Vivian: Okay?
06:00:620Jacopo Vivian: So it means that if you if you work with the
06:12:240Jacopo Vivian: if if your design temperature is minus 5 degrees.
06:16:860Jacopo Vivian: And in the technical data of the, for example, let's take the
06:32:650Jacopo Vivian: yes, it's this.
06:38:370Jacopo Vivian: okay, okay. But here we don't have in the table that it does not specify the condition.
06:49:200Jacopo Vivian: You will find it in the legend.
06:55:10Jacopo Vivian: Okay, you need to download the catalogs for a heat pump. Okay?
07:00:870Jacopo Vivian: And you will find a similar table like this one
07:05:510Jacopo Vivian: there you will also find what are the nominal conditions at which the heating capacity is referred.
07:14:620Jacopo Vivian: For example, for this heat pump.
07:17:800Jacopo Vivian: For this model we have a 5.76 kilowatt, at which temperature
07:26:170Jacopo Vivian: you will find it that you will find that information in the catalog. You just need to read the what the 3 E means. Okay.
07:34:460Jacopo Vivian: similarly, you will find it for any other heat pump catalog.
07:41:290Jacopo Vivian: So you either choose the standard method. Okay, the peak, load the calculation.
07:53:660Jacopo Vivian: or you do something more elaborate by
07:58:70Jacopo Vivian: starting from the heating demand. Like, I did. Okay, of course, without drawing the lines of the temperature of the screen.
08:08:260Jacopo Vivian: But in both cases you consider 10% more of power due to the defrosting cycles.
08:19:450Jacopo Vivian: Okay?
08:21:229Jacopo Vivian: And you choose a heat pump, a model that you think is suitable for your case, so they only
08:32:51Jacopo Vivian: error that you can make in this procedure
08:37:560Jacopo Vivian: is that you consider this number without considering
08:44:689Jacopo Vivian: the boundary condition, it refers to meaning the outer air condition. So if a 5 point
08:52:729Jacopo Vivian: 6 sorry, 5.7 6 is referred, for example, to 2 Celsius degrees.
09:04:760Jacopo Vivian: Then you should consider what happens at minus 5.
09:09:580Jacopo Vivian: Is this heat pumper suitable to minus 5.
09:15:250Jacopo Vivian: You find this information in the heat pump catalog.
09:18:750Jacopo Vivian: Remember, you need to look at
09:22:979Jacopo Vivian: at these charts. If you find them.
09:26:529Jacopo Vivian: Otherwise, you will find minimum and maximum outdoor air temperature
09:34:109Jacopo Vivian: or minimum and maximum evaporating and condensing temperature. You need to check that. Your machine is suitable for your conditions.
09:44:740Jacopo Vivian: So, for example, if you have radiators. No, you don't have radiators because you have the floor heating system. So
09:51:340Jacopo Vivian: you don't have problems on the condenser point of view. You just need to consider the evaporator side.
10:03:130Jacopo Vivian: and you need to calculate the
10:05:700Jacopo Vivian: thermal output. So the heat capacity at the design conditions, how, by using a method like this one
10:17:780Jacopo Vivian: or by making a regression.
10:21:50Jacopo Vivian: If you have 2 points.
10:23:340Jacopo Vivian: Okay, for example, if okay, I will let me try.
10:33:730Jacopo Vivian: Use this.
11:10:190Jacopo Vivian: So
11:15:960Jacopo Vivian: you see my screen. Yes.
11:23:270Jacopo Vivian: if you have a for example,
11:32:740Jacopo Vivian: the heat capacity from the catalog at
11:37:790Jacopo Vivian: 2 degrees and 7 degrees outdoor temperature. Okay.
11:47:740Jacopo Vivian: you find from the catalog that the heat pump output is, I don't know.
11:54:410Jacopo Vivian: 5.7 and 6.8.
12:01:820Jacopo Vivian: For example. Okay, so in this case you have 2 points.
12:08:610Jacopo Vivian: You have here at 2 you have 5.7,
12:14:390Jacopo Vivian: and at 7 degrees you have 6.8.
12:20:580Jacopo Vivian: So if it is not specified in the catalog. I expect you to find the
12:29:680Jacopo Vivian: a pointer which is closer to the which is on the design conditions. Okay?
12:39:950Jacopo Vivian: And this point should be higher or equal than the peak load.
12:51:410Jacopo Vivian: plus 10% of the defrosting.
13:01:580Jacopo Vivian: How do you reach this point with the X
13:06:30Jacopo Vivian: you either make a regression, or you can use the method that is on the slide with the Carnot efficiency.
13:14:770Jacopo Vivian: Okay, it is a
13:23:580Jacopo Vivian: here, this slide.
13:28:410Jacopo Vivian: So this is required. So you choose
13:36:120Jacopo Vivian: the nominal load of the heat, you. You select the heat bumper where this power is a high enough.
13:50:490Jacopo Vivian: and then you verify that the heat pump is suitable for your application.
13:58:320Jacopo Vivian: So if you can find it
14:02:186Jacopo Vivian: on the catalog you find the envelopes like those that I showed before.
14:08:360Jacopo Vivian: or you just find the minimum and maximum temperatures.
14:14:470Jacopo Vivian: It will always be suitable spoiler, because you are working with the
14:20:00Jacopo Vivian: an air source heat pump for
14:23:296Jacopo Vivian: our climate, for with 4th floor heating system. So
14:28:730Jacopo Vivian: unless you choose a very strange heat pumps.
14:32:350Jacopo Vivian: it is, it will be suitable. But I want you to check, because in other cases
14:39:800Jacopo Vivian: it can't be not suitable. Okay, for example.
14:44:230Jacopo Vivian: if you want to work with the heat pump and radiator systems.
14:50:380Jacopo Vivian: and you need to deliver heat at 70 degrees. Not all the heat pumps are suitable. Okay?
14:58:50Jacopo Vivian: So although in your case it will be suitable, please make this check and
15:09:190Jacopo Vivian: So you already know how to calculate the peak load right with the standard.
15:17:500Jacopo Vivian: Of course, if you want to do something more.
15:23:880Jacopo Vivian: To work with the.
15:26:320Jacopo Vivian: to to find the power with the heat demand, like I did, you are free to do it.
15:32:420Jacopo Vivian: Okay, it is not
15:37:600Jacopo Vivian: It is not required. It's up to you
15:41:90Jacopo Vivian: this. What is required is the normal calculation of the peak load. The selection of the heat pump with any manufacturer is fine.
15:51:930Jacopo Vivian: Just need to check the power, the suitability for the temperatures.
15:58:170Jacopo Vivian: And you can calculate. And you can specify the cop.
16:05:280Jacopo Vivian: Okay, the cop that that you expect to to have, I think,
16:16:780Jacopo Vivian: that's it. For for the reporter.
16:20:340Jacopo Vivian: we still do you have any questions on this part?
16:28:90Jacopo Vivian: Everything is clear, okay, perfect. So we've we finish now the the generation systems
16:43:760Jacopo Vivian: by looking at some schematics that I found on Internet.
17:27:460Jacopo Vivian: Okay.
17:31:430Jacopo Vivian: so this is a an example of a typical supply station with a gas boiler.
17:39:280Jacopo Vivian: This is the gas boiler, the let me take the pointer.
18:01:840Jacopo Vivian: Okay, so this is the gas boiler here.
18:06:830Jacopo Vivian: Can you see the pointer? It's not very much
18:16:590Jacopo Vivian: this one.
18:21:140Jacopo Vivian: Yes. So this is the gas boiler.
18:25:320Jacopo Vivian: This is the burner of the gas boiler.
18:29:330Jacopo Vivian: Okay, you have.
18:35:00Jacopo Vivian: You have the primary circuit. So the supply pipe here
18:40:540Jacopo Vivian: with the pump on the flow on the supply.
18:44:730Jacopo Vivian: Then you have the the aerator
18:49:700Jacopo Vivian: and you have the hydraulic separator.
18:54:190Jacopo Vivian: Then you have this large separator. On the return
18:59:420Jacopo Vivian: you have the supply and return manifold.
19:03:710Jacopo Vivian: and from the manifold you have the secondary circuit.
19:11:10Jacopo Vivian: The secondary circuit has another pump that is regulated in order to have.
19:21:810Jacopo Vivian: together with this 3 way valve.
19:24:550Jacopo Vivian: This is a mixing valve that mixes the return
19:29:470Jacopo Vivian: coming from the terminal units with the supply coming from the boiler.
19:35:610Jacopo Vivian: Okay?
19:37:990Jacopo Vivian: And so here the flow. So the flow to the terminal unit is set by this pump.
19:47:10Jacopo Vivian: Okay?
19:48:320Jacopo Vivian: And the temperature to the terminal units is decided by this three-way valve that is, a
19:55:320Jacopo Vivian: before the secondary pump.
20:01:320Jacopo Vivian: and then
20:02:970Jacopo Vivian: from the same manifold, we have the water reaching the hot water tank for domestic hot water production.
20:11:730Jacopo Vivian: Okay, here we have another circulator, because in this case, you see.
20:17:350Jacopo Vivian: we have the on offer of the circulator
20:21:990Jacopo Vivian: based on the temperature in the storage in the hot water tank.
20:27:640Jacopo Vivian: meaning that this pump will be
20:30:920Jacopo Vivian: switched on only when the water in the tank will drop below a certain value.
20:39:160Jacopo Vivian: Okay?
20:40:990Jacopo Vivian: And when it switches on there is no problem, because we have a head hydraulic separator here.
20:48:840Jacopo Vivian: So the flow rate in this circuit is independent from the flow rate in the primary circuit.
21:00:540Jacopo Vivian: Okay, on the secondary side of the of the tank we have a
21:08:320Jacopo Vivian: the water coming from the aqueduct here.
21:13:290Jacopo Vivian: Expansion vessel.
21:16:20Jacopo Vivian: And this is a mixed hot water tank, because we accumulate the hot water directly in the tank.
21:25:280Jacopo Vivian: Remember, we can have a legionella problem in this case.
21:32:160Jacopo Vivian: Okay, from the boiler. Sorry from the tank. We have
21:39:60Jacopo Vivian: 2 pipes. One is the supply.
21:43:880Jacopo Vivian: One is the in this case.
21:51:620Jacopo Vivian: it should be the recirculation pipe.
21:58:90Jacopo Vivian: but I'm not sure in this case we have the
22:02:540Jacopo Vivian: so to the in this case, to the users. We supply the cold water.
22:10:890Jacopo Vivian: Okay, the hot water.
22:14:590Jacopo Vivian: And we have this recirculation.
22:19:140Jacopo Vivian: This is typically done to maintain.
22:24:490Jacopo Vivian: A hot circuit on the secondary side, so that the users do not
22:29:840Jacopo Vivian: wait too much for the hot water.
22:35:780Jacopo Vivian: and here we have a mixing valve on the supply to regulate the the temperature to the users.
22:48:700Jacopo Vivian: Okay?
22:49:960Jacopo Vivian: Because in general, we can have a
22:52:870Jacopo Vivian: very high temperature in the tank.
22:55:650Jacopo Vivian: We don't want the user to tap hot water and receive 60 degrees.
23:01:460Jacopo Vivian: Okay?
23:02:400Jacopo Vivian: So we have a three-way valve
23:05:170Jacopo Vivian: in mixing mode on the supply.
23:13:140Jacopo Vivian: Okay?
23:14:510Jacopo Vivian: And then why do we have this pipe here?
23:22:460Jacopo Vivian: Because if there are leakages, or, if we need to ex
23:31:20Jacopo Vivian: blow, for example, some air out of the circuit we open.
23:36:580Jacopo Vivian: and we will have some pressure drop due to the discharge of the system. So we also need a pipe that is charging the system again.
23:49:960Jacopo Vivian: And this is the pipe right?
23:56:150Jacopo Vivian: So this is a traditional heat supply station.
24:05:520Jacopo Vivian: This is something closer to what you have, because you have
24:11:260Jacopo Vivian: the monoblock air source heat pump. Remember that if it is.
24:17:100Jacopo Vivian: I think everything in one component is a model block.
24:21:730Jacopo Vivian: Okay, with all the components, meaning the compressor, the evaporator, the condenser, and the the lamination valve in the
24:32:600Jacopo Vivian: in the same unit which goes outdoor.
24:36:840Jacopo Vivian: We have a the circulator of the primary circuit here inside the monoblock.
24:46:540Jacopo Vivian: Okay, that means we do not need
24:52:540Jacopo Vivian: a separate heat pump on the primary side, because it is already in the monoblock heat pump.
25:01:640Jacopo Vivian: So we have the supply water.
25:07:30Jacopo Vivian: Here we have the diarator again.
25:10:460Jacopo Vivian: and here we have a three-way valve here.
25:15:580Jacopo Vivian: How does the resolve work?
25:21:710Jacopo Vivian: You see? On one hand, it
25:25:60Jacopo Vivian: sends the water to the phone coils.
25:28:630Jacopo Vivian: On the other hand, it since the water today, hot water tank.
25:37:500Jacopo Vivian: So in this case we have a three-way valve that is
25:44:690Jacopo Vivian: either fully open or fully closed.
25:48:690Jacopo Vivian: If it is fully open, it will let the flow go to the fun coil.
25:56:240Jacopo Vivian: If it is fully closed, it closes the heating circuit and opens the domestic water circuit.
26:05:330Jacopo Vivian: This is the typical configuration of heat pumps. They have a three-way valve
26:12:670Jacopo Vivian: that decides the direction, and normally the priority is on the hot water, especially in a residential application.
26:23:260Jacopo Vivian: In a non residential application you can find other strategies, but in residential applications
26:32:390Jacopo Vivian: you always find the priority on the domestic hot water, because people don't want to wait 2 h for the shower to be hot.
26:41:740Jacopo Vivian: so as soon as we have
26:45:260Jacopo Vivian: cold tank, cold water in the tank.
26:50:610Jacopo Vivian: this valve will deviate the flow to the tank so that we heat it up again.
27:00:770Jacopo Vivian: If the users are not requiring are are not asking for hot water.
27:08:590Jacopo Vivian: It will take more time between these 2 cycles.
27:13:600Jacopo Vivian: because we only have the heat losses from the tank.
27:18:80Jacopo Vivian: If we have request for hot water from the users.
27:23:880Jacopo Vivian: This case we will have
27:29:900Jacopo Vivian: higher frequency of the opening of this three-way valve.
27:35:500Jacopo Vivian: and then we have something interesting here on the return of the
27:44:811Jacopo Vivian: so 1st of all, here we have.
27:52:260Jacopo Vivian: I think this is a a just for pressure control.
27:56:710Jacopo Vivian: Okay, differential pressure controller.
28:01:420Jacopo Vivian: And here we have something interesting on the return
28:06:650Jacopo Vivian: of the phone calls here with because we have a an inertial component.
28:16:530Jacopo Vivian: So here we have a small tank to add inertia to the system so that we can
28:24:350Jacopo Vivian: better control the on off of the heat pump.
28:29:490Jacopo Vivian: Okay?
28:31:470Jacopo Vivian: In fact, this is not with the floor heating system, where we have a
28:36:940Jacopo Vivian: a lot of thermal inertia in the system, as I showed before.
28:41:590Jacopo Vivian: Here we are. We have phone calls.
28:44:540Jacopo Vivian: So all the inertia is given by the water in the pipes.
28:50:30Jacopo Vivian: And that's it.
28:52:960Jacopo Vivian: Okay?
28:55:280Jacopo Vivian: Finally, the last one
29:02:220Jacopo Vivian: is this one.
29:04:340Jacopo Vivian: Well, we always have the monoblock air source heat pump on the primary side.
29:10:100Jacopo Vivian: We have in this case the three-way valve
29:19:960Jacopo Vivian: here.
29:22:350Jacopo Vivian: Okay, that sends the flow either to the manifold or to the tank.
29:32:900Jacopo Vivian: In this case the manifold supplies either
29:37:580Jacopo Vivian: the heating system. You see, you have a zone manifold here with the
29:45:620Jacopo Vivian: so this is the central manifold, and this is the zone manifold. The zone manifold supplies in this case a fun coil circuit and the floor heating circuit
29:57:570Jacopo Vivian: right?
30:00:60Jacopo Vivian: And you have pump on the secondary side.
30:06:320Jacopo Vivian: This, the other circuit, starting from the central manifold, is going to the air handling units.
30:15:900Jacopo Vivian: Okay?
30:19:730Jacopo Vivian: And back to the hydraulic separator.
30:24:900Jacopo Vivian: Okay, and back to the heat pump.
30:29:700Jacopo Vivian: In this case we have something interesting on the domestic or Twitter side.
30:35:50Jacopo Vivian: because we have solar thermal collector
30:39:220Jacopo Vivian: connected to a second to a second coil inside the thermal storage.
30:47:220Jacopo Vivian: Please note that the solar thermal collector coil is
30:54:200Jacopo Vivian: in the lower part of the thermal storage.
30:57:780Jacopo Vivian: because in this case you typically have stratification in the tank.
31:04:260Jacopo Vivian: and you want the coil to be as cold.
31:08:310Jacopo Vivian: cool down as much as possible.
31:11:290Jacopo Vivian: because otherwise we send back the hot water to the solar collector.
31:17:490Jacopo Vivian: which is not able to extract heat from the panel.
31:23:70Jacopo Vivian: So that's why we
31:25:350Jacopo Vivian: use the solar coil in the bottom part of the tank, because usually due to the stratification. This is the colder part.
31:36:150Jacopo Vivian: Okay?
31:38:390Jacopo Vivian: So these are simplified schematics of the of Hvac systems that
31:47:670Jacopo Vivian: you are now able to read yourself.
31:54:180Jacopo Vivian: That's it for today.
31:58:300Jacopo Vivian: next lecture will be tomorrow about district heating system, and then you have the final lecture
32:05:270Jacopo Vivian: on Wednesday with Professor decal decarli.
32:11:190Jacopo Vivian: Then I remember that Monday next week there is a seminar on data centers, and Tuesday
32:20:460Jacopo Vivian: last, but not least, Tuesday. Next week
32:24:520Jacopo Vivian: we have the text technical visit.
32:27:620Jacopo Vivian: So please register yourself on moodle for the technical visit.
32:33:320Jacopo Vivian: Okay.
32:34:430Jacopo Vivian: because we need to have the list. Please do it today or tomorrow, not later, because we need to send the list
32:42:990Jacopo Vivian: so that the offices are informed about the participants.
32:48:10Jacopo Vivian: Okay, that's it for today. Thank you.