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00:02:340Jacopo Vivian: Okay, the date is wrong, but the content is the same.
00:13:830Jacopo Vivian: Okay? So we were talking about how to distribute the the energy to different parts of the building with the distribution systems. And we said that
00:32:140Jacopo Vivian: we we need to balance the system because we have continuous and localized pressure losses. So now we complete this part by
00:44:972Jacopo Vivian: mentioning some values. Okay, that can be used for sizing
00:52:130Jacopo Vivian: based on the maximum pressure losses that we expect to have good issues.
01:03:570Jacopo Vivian: the content. You know that the desktop p
01:06:910Jacopo Vivian: depends on a friction factor that depends on the material, on a.
01:17:380Jacopo Vivian: on the length.
01:19:960Jacopo Vivian: It's inverse inversely proportional to the hydraulic diameter.
01:25:540Jacopo Vivian: and then the density and the square of the velocity
01:31:100Jacopo Vivian: and localized losses do not depend on length and diameter. They depend on a coefficient beta that is given for each
01:42:560Jacopo Vivian: obstruction to the flow.
01:44:790Jacopo Vivian: For example, fitting a valve heat exchanger even a terminal unit.
01:51:630Jacopo Vivian: Okay, here.
01:57:520Jacopo Vivian: this data piece here.
01:59:920Jacopo Vivian: It's the last terminal unit. So you can see there's a localized fraction drop
02:06:250Jacopo Vivian: between the supply and the return to the last state that we are used.
02:10:840Jacopo Vivian: Okay, okay? So the friction factor depends on this, on the
02:23:270Jacopo Vivian: scabrezza roughness, if I remember correctly, of the pipe.
02:29:770Jacopo Vivian: And so the ratio between the roughness. Yes, it's written the relative pipe roughness.
02:36:600Jacopo Vivian: It's the ratio between the roughness and the diameter, and on Reynolds number.
02:45:710Jacopo Vivian: You know that rhino Reynolds number depends on velocity, diameter, density and viscosity.
02:57:990Jacopo Vivian: Okay?
02:59:70Jacopo Vivian: So the viscosity of a fluid
03:02:640Jacopo Vivian: is impacting the pressure losses along sphere in case you know, the
03:14:850Jacopo Vivian: moody. From the moody diagram we know that there are different
03:24:290Jacopo Vivian: flows depending on the value of the Reynolds number. If the Reynolds number is low, means that if the velocity is very low.
03:34:550Jacopo Vivian: we have laminar flow.
03:37:610Jacopo Vivian: That means that in this case the friction factor only depends on the Reynolds number.
03:43:930Jacopo Vivian: In case the Reynolds number is high, typically higher velocity.
03:50:400Jacopo Vivian: We don't only consider the Reynold number, but we also consider the relative pipe pregnancy.
03:57:340Jacopo Vivian: and this is a Colley Brooks correlation.
04:01:560Jacopo Vivian: so you can look at it on the moody diagram. Here you see the lam in the Laminar
04:09:760Jacopo Vivian: flow region. You only have a line that give you the
04:14:860Jacopo Vivian: friction factor on the left as
04:18:940Jacopo Vivian: as a function of the Reynolds number on the X-axis and in the
04:27:950Jacopo Vivian: turbulence region. That means in the right part of the moody diagram. You don't only consider the Reynolds number meaning, for example, this value here, but also
04:41:520Jacopo Vivian: you need to cross one of these lines. Each of these line represents a relative roughness.
04:47:650Jacopo Vivian: So, given the pipe material and characteristic, you have the roughness or the relative roughness, and you decide
04:59:890Jacopo Vivian: where to cross. The vertical line where the vertical lines
05:08:120Jacopo Vivian: crosses this line of constant relative roughness, and you find the corresponding friction factor.
05:17:360Jacopo Vivian: So the absolute roughness for some materials. Let's look at it for copper aluminum.
05:29:50Jacopo Vivian: You have 0 point 0 0 1 0 point 0 0 2
05:36:765Jacopo Vivian: for stainless steel. You have the same. Okay, 0 point 0 0 1 5
05:47:730Jacopo Vivian: for carbon steel. You have an order or order of magnitude. Okay.
05:56:320Jacopo Vivian: of course, if the pipe is corroded, the roughness will increase, cast iron, and so on
06:08:150Jacopo Vivian: for concrete. You know you can have concrete
06:12:430Jacopo Vivian: not to distribute the heating and cooling to buildings, but maybe to distribute the water. Okay, you have
06:23:830Jacopo Vivian: millimeters, roughness reaching 1 concrete even more.
06:31:190Jacopo Vivian: Okay? So we are interested in these materials. Basically copper and plastic.
06:39:430Jacopo Vivian: Okay, so that's why we can use simplified correlations that give us the
06:46:420Jacopo Vivian: pressure drop as a function of the material
06:51:140Jacopo Vivian: for commercially available copper, enox, multi-layer plastic pipe.
06:58:740Jacopo Vivian: You can consider these pipes to be low roughness pipes where you can apply this this correlation
07:12:460Jacopo Vivian: that gives you the friction factor as a function of the Reynolds number.
07:18:690Jacopo Vivian: so the relative roughness is so low that even with turbulent flow we can ignore its effect.
07:31:920Jacopo Vivian: If we don't want to calculate the
07:36:70Jacopo Vivian: the Delta P based on the friction factor. But we directly want the formula to calculate the Delta P.
07:46:420Jacopo Vivian: For continuous pressure losses. You can find it. Using this formula, where
07:52:260Jacopo Vivian: this is an empirical correlation, it's using technical units and not
07:58:320Jacopo Vivian: international system units. So please take care if you use this kind of formulas. This is not the only one you can find. Other
08:07:890Jacopo Vivian: technical
08:10:670Jacopo Vivian: Other empirical correlations for specific materials always look at the
08:20:770Jacopo Vivian: system units, and convert, if necessary.
08:26:330Jacopo Vivian: for other materials like iron and galvanized steel pipes.
08:32:159Jacopo Vivian: You have this other correlation.
08:35:390Jacopo Vivian: Okay?
08:36:510Jacopo Vivian: Again, this is the friction factor, or you can find directly the Delta P
08:42:280Jacopo Vivian: for continuous pressure losses. In this case, and also in the previous case, the Delta P is given in millimeters of water column per meter.
08:55:640Jacopo Vivian: So the meter refers to the length of the pipe
08:59:660Jacopo Vivian: and millimeter of water. Column is an alternative, an alternative unit for
09:11:500Jacopo Vivian: pressure that is typically used in
09:15:320Jacopo Vivian: hydronic system like meters of water column. You have already seen it with the Professor Bakari.
09:24:00Jacopo Vivian: When we were speaking about you. Were you were speaking about the
09:32:420Jacopo Vivian: the maximum delta p of radian systems between supply and return.
09:39:880Jacopo Vivian: Okay, remember, he told you around one meter of water column for each circuit of the radian system.
09:49:780Jacopo Vivian: I told you, okay, you can also consider higher Delta P, until more or less 3 meters
09:57:780Jacopo Vivian: of what their problem.
09:59:870Jacopo Vivian: Okay, just to give you a range.
10:02:520Jacopo Vivian: That means, if you do calculations
10:05:190Jacopo Vivian: and you have a 0 point 0 1 meter. That means 1 cm of water column.
10:11:650Jacopo Vivian: Maybe you should consider having a a lower number of secrets
10:19:680Jacopo Vivian: and the other way around, if you have one bar.
10:23:70Jacopo Vivian: Okay, so remember, it's very useful in practice to be familiar with this technical unit.
10:36:440Jacopo Vivian: Also, rhino's number that we use in this correlation depends on viscosity.
10:43:220Jacopo Vivian: We have seen, the viscosity is at the denominator of the Reynolds number and viscosity depends on temperature.
10:56:440Jacopo Vivian: So the rhino's number of water at 8 degrees.
11:02:470Jacopo Vivian: It's not the same of the viscosity of water at the 55 degrees.
11:13:210Jacopo Vivian: This will change the Delta. P.
11:17:30Jacopo Vivian: Okay, so you can, you can have a look
11:24:400Jacopo Vivian: to what happens. I gave you this diagrams here for the same diameter.
11:32:360Jacopo Vivian: Okay, you can assume a certain velocity.
11:35:990Jacopo Vivian: and you can calculate the Delta P of the continuous pressure pressure losses at the
11:44:990Jacopo Vivian: for a heating system. With radiators.
11:48:850Jacopo Vivian: you can assume 70 degrees on the supply line and the
11:55:230Jacopo Vivian: continuous pressure losses of the same system with the same diameter, the same
12:04:340Jacopo Vivian: velocity of the water in the pipes with the 8 Celsius degrees. Okay, you will see
12:15:500Jacopo Vivian: the change is significant also. Density changes with the with the temperature.
12:25:530Jacopo Vivian: But viscosity has a more significant effect than density. Okay, on the pressure losses.
12:38:770Jacopo Vivian: These are okay. These are some values
12:42:960Jacopo Vivian: I didn't remember. I have them. Here you can see
12:49:00Jacopo Vivian: at 20 degrees. You have a kinematic viscosity of 1 10 power, minus 6 m² per second
13:01:260Jacopo Vivian: at 80 degrees.
13:03:330Jacopo Vivian: We have 0 point 3. So it's 3 times lower.
13:08:20Jacopo Vivian: Okay?
13:09:650Jacopo Vivian: So it's it's quite relevant to consider the correct temperature, whereas
13:17:320Jacopo Vivian: density, you can see it changes from 1,000 to 9, 7, 1. So 3%
13:28:80Jacopo Vivian: on kinematic viscosity for the same delta T changes by 3 times meaning 300%
13:38:830Jacopo Vivian: density changes by 3%.
13:42:60Jacopo Vivian: So the effect of viscosity is in this range is
13:49:290Jacopo Vivian: 100 times more than the effect of density.
13:55:300Jacopo Vivian: Okay, so you can verify, if
14:03:10Jacopo Vivian: calculating, the pressure losses for colder water
14:08:360Jacopo Vivian: will increase or decrease the pressure losses.
14:13:500Jacopo Vivian: This is up to you. So you can apply the
14:18:320Jacopo Vivian: average between 0 and 20 degrees and the average between 60 and 80 degrees. In the 1st case you are considering cold water of the cooling system. In the second case, you are considering hot water to the radiators.
14:33:700Jacopo Vivian: And you you assume to have low roughness pipes.
14:38:630Jacopo Vivian: Okay?
14:39:650Jacopo Vivian: And you see how the continuous pressure loss changes.
14:46:900Jacopo Vivian: Okay.
14:50:510Jacopo Vivian: high roughness pipe have a different correlation. I didn't report it here because it is not very relevant for us.
15:00:350Jacopo Vivian: What is the expected value that we should find?
15:05:740Jacopo Vivian: Okay?
15:08:320Jacopo Vivian: as a rule of thumb, you can consider a range between 100 400 Pascal per meter.
15:16:970Jacopo Vivian: I'm talking about continuous pressure losses. Okay? So we are talking about sizing.
15:24:00Jacopo Vivian: We size the system a distribution line to have a
15:29:950Jacopo Vivian: certain, we, we should fix something. We need to decide the diameter.
15:35:290Jacopo Vivian: Okay, so we need to decide the diameter of a distribution line.
15:41:780Jacopo Vivian: I expect to have a continuous pressure loss between 100 400 Pascal per meter.
15:56:20Jacopo Vivian: The rain. Okay, this is, for you have it
16:01:50Jacopo Vivian: in this case. This is taken from the usher handbook.
16:07:380Jacopo Vivian: This will give you the if you fix.
16:13:290Jacopo Vivian: If you fix the diameter and the velocity and the
16:18:120Jacopo Vivian: and the material. In this case, commercial steel pipe, you find the pressure drop.
16:24:980Jacopo Vivian: It's an alternative way to calculating with the empirical correlations.
16:30:910Jacopo Vivian: Okay, but I expect to find this more or less the same value.
16:36:550Jacopo Vivian: Okay, so the other way around, if you're sizing, you fix the Delta P Pascal per meter.
16:50:590Jacopo Vivian: for example, 200, and you
16:58:450Jacopo Vivian: you choose the diameter in order to have the desired flow rate.
17:04:690Jacopo Vivian: Okay, remember, you always start from the demand.
17:11:60Jacopo Vivian: Both in the cooling and heating we start from the building envelope. We start from a transmission and ventilation losses.
17:19:220Jacopo Vivian: We calculate the heat demand and the cooling demand. We calculate the heating peak load and the cooling peak load. This is a thermal power.
17:28:420Jacopo Vivian: Then we need to apply a delta T depending on which terminal units we have.
17:37:350Jacopo Vivian: Typically, we have, for example, a phone call supply 45, return 40.
17:44:470Jacopo Vivian: Okay, Delta T is 5.
17:48:190Jacopo Vivian: Given that heating flow, the peak load and they
17:55:210Jacopo Vivian: delta T, we find the flow rate.
17:58:430Jacopo Vivian: How can I size this distribution system? We are talking about distribution systems of heating and cooling.
18:06:520Jacopo Vivian: I know the flow rate.
18:08:930Jacopo Vivian: I need to have a reasonable continuous pressure loss.
18:14:270Jacopo Vivian: So I must be in this range.
18:16:700Jacopo Vivian: Okay, between 100 400.
18:20:590Jacopo Vivian: So I fix it.
18:22:340Jacopo Vivian: Say, for example, 200.
18:25:90Jacopo Vivian: I know the flow rate.
18:27:680Jacopo Vivian: Imagine it is 20 liters per second.
18:32:320Jacopo Vivian: So I I move here to this point. Here, this point. The diameter is 125
18:46:580Jacopo Vivian: This is the diameter.
18:49:210Jacopo Vivian: If you apply the empirical correlation I showed before.
18:53:330Jacopo Vivian: It's the same. You will find a similar diameter.
18:58:720Jacopo Vivian: But of course it's easier if you have these, Ross.
19:04:610Jacopo Vivian: Okay, this is for another material copper plastic.
19:16:620Jacopo Vivian: Of course, they are different, because we need to consider the relative roughness.
19:23:880Jacopo Vivian: Okay, so we have a different chart for each by the material.
19:31:480Jacopo Vivian: We talked about the continuous pressure losses. Now, we need to talk about localized pressure losses.
19:38:740Jacopo Vivian: Also here, you need to have a technical support of
19:44:960Jacopo Vivian: in this case. I use the Calafi handbooks.
19:49:110Jacopo Vivian: Okay, Caletti is just a name of a brand Italian brand.
19:54:980Jacopo Vivian: but you can find also other manufacturers that provide that provides similar values for different sivads, fittings,
20:13:430Jacopo Vivian: and for each of them you find the coefficient Beta Beta will give you.
20:22:200Jacopo Vivian: There's the P.
20:23:890Jacopo Vivian: Given the beta and the velocity. You have the Delta P connected to that pressure drop.
20:33:990Jacopo Vivian: Okay, here again, this is not for valves. This is for Benson
20:41:250Jacopo Vivian: elbows. Section changes the joints, and so on.
20:47:30Jacopo Vivian: You have data provided by technical literature.
20:53:140Jacopo Vivian: Okay, technical literature is very important for the design of Hvac systems.
21:03:220Jacopo Vivian: This is another example from another source.
21:07:630Jacopo Vivian: We have from Icar, which is the Association Italian Association of Manufacturers of Hvac Systems. Basically.
21:21:50Jacopo Vivian: Okay, there is a handbook called meaning with Iker
21:25:250Jacopo Vivian: in the handbook. We have these values of beta.
21:30:450Jacopo Vivian: Good.
21:33:60Jacopo Vivian: Okay. Again, the rule of thumb is to have
21:39:120Jacopo Vivian: between 100 400 Pascal per meter.
21:48:470Jacopo Vivian: The mean value of 250 Pascal per meter is a commonly used target.
21:56:400Jacopo Vivian: Okay?
21:57:650Jacopo Vivian: So if you start from scratch.
22:00:410Jacopo Vivian: you can use this value to size a system.
22:06:610Jacopo Vivian: But you also need to consider.
22:10:280Jacopo Vivian: Are there practical limits like maximum velocity, for especially for piping close to the user
22:23:330Jacopo Vivian: meaning the pipes that are closer to the terminal unit, because this is where the people live
22:30:500Jacopo Vivian: or spend their time having high velocity.
22:34:900Jacopo Vivian: having low velocity. Here is more important than having low velocity in the heat supply station, because noise is not
22:47:580Jacopo Vivian: important in the supply station as it is here. Okay. So 1.2 meters per second is a practical limit that you need to consider beyond
23:00:280Jacopo Vivian: the maximum delta p that I gave you before, so
23:06:360Jacopo Vivian: especially for pipes with the nominal diameter lower than 50 for bigger pipes you might have higher velocities.
23:21:490Jacopo Vivian: And so,
23:24:810Jacopo Vivian: What is the advantage of having higher velocity?
23:34:930Jacopo Vivian: We don't want to lose energy typically in distribution systems. So this is a disadvantage, not an advantage.
23:47:240Jacopo Vivian: And so lower cost.
23:49:610Jacopo Vivian: So higher velocity means higher flow rate.
23:55:540Jacopo Vivian: And so if we have a higher
23:59:630Jacopo Vivian: velocity, we can have a lower diameter, which means smaller pipe, which means lower investment costs.
24:09:140Jacopo Vivian: which is important, especially in the big pipes that are close to the heat supply station.
24:16:580Jacopo Vivian: Okay?
24:17:630Jacopo Vivian: So when we move closer to the user, we spend more focus on the comfort.
24:27:830Jacopo Vivian: We don't want noise here.
24:30:450Jacopo Vivian: When we go to the technical side of the building, we want to reduce costs.
24:38:960Jacopo Vivian: Okay, but never exceed the 400 Pascal per meter. Otherwise, we need to spend more during the operation
24:51:980Jacopo Vivian: because we will have a lot of
24:55:750Jacopo Vivian: electricity needs of the circulation pumps.
25:00:60Jacopo Vivian: Okay.
25:04:840Jacopo Vivian: then we have other problems like
25:10:900Jacopo Vivian: So because noise is not only caused by velocity in the pipes.
25:19:240Jacopo Vivian: but also by the presence of free air
25:23:390Jacopo Vivian: and the free air can cause cavitation.
25:28:540Jacopo Vivian: Okay? Because it creates regions in the closed circuit with low pressure.
25:37:110Jacopo Vivian: Okay, we will see better talking about bounce.
25:46:20Jacopo Vivian: Anyway, we want to avoid to have air
25:50:70Jacopo Vivian: in the hydronics equit for a number of reasons, not only for the Mahoizo.
25:58:350Jacopo Vivian: This is typically the situation. When where you start your heating system in your apartment
26:06:430Jacopo Vivian: on the 15th of October, and the radiator the boiler is on.
26:16:480Jacopo Vivian: But the radiator is called.
26:19:340Jacopo Vivian: Why?
26:20:830Jacopo Vivian: Because during the summer there was no pressure in the system.
26:28:450Jacopo Vivian: and some air leaked inside the pipes.
26:32:730Jacopo Vivian: This air will make a
26:36:770Jacopo Vivian: some air bubble that prevent the correct circulation of the heat carrier fluid in the terminal units like your radiators, and the radiator is not heating up.
26:50:410Jacopo Vivian: That's why you need to remove the air.
26:54:180Jacopo Vivian: Now in your apartment. You can do it manually by opening a valve. Okay, I don't know if you ever did it. When I was a student I did it quite often, because
27:05:710Jacopo Vivian: every time I used to live in a very old apartment every time we had the air in the circuit.
27:14:470Jacopo Vivian: and I need to go there and remove all the air by opening a valve close to the
27:20:950Jacopo Vivian: radiator. Okay, and waiting for all the air to
27:27:450Jacopo Vivian: to flow away, to flow out.
27:31:490Jacopo Vivian: And then you close the circuit, and you give pressure
27:36:550Jacopo Vivian: to the secret, mean meaning that you open a valve
27:42:450Jacopo Vivian: close to the boiler that makes the
27:48:340Jacopo Vivian: that increases the mass of water in the in the system.
27:53:390Jacopo Vivian: Okay.
27:54:510Jacopo Vivian: but in a bigger, bigger cases, bigger buildings. We don't do it manually. We have some components that are responsible of removing the air. Okay, like air separation units.
28:09:680Jacopo Vivian: Okay, let me finish just this slide.
28:13:620Jacopo Vivian: So we said that the air is undesirable, not only because
28:21:489Jacopo Vivian: it cause noise. 1st is the 1st thing we we said, second is because it prevents the correct flow in some parts of the secret.
28:32:720Jacopo Vivian: and this is a problem, especially if the heat current fluid does not reach correctly
28:38:680Jacopo Vivian: all the terminal units, and 3, rd which is the second year.
28:45:390Jacopo Vivian: It allows oxygen to react with piping material. If you and this will lead to corrosion, because air
28:55:900Jacopo Vivian: is made 23% in mass by oxygen and oxygen will
29:04:140Jacopo Vivian: start an oxidation reaction which will corrode the pipes.
29:09:170Jacopo Vivian: For all this reason we need to remove the air from the heat from the circuit.
29:15:410Jacopo Vivian: so we install the air separator. Where do we install it? We install it in the point of lowest pressure
29:24:620Jacopo Vivian: or highest temperature.
29:27:430Jacopo Vivian: Highest temperature means on the outlet of the of the generation unit
29:35:950Jacopo Vivian: for heating systems. Lowest pressure means before the main circulation pump.
29:43:760Jacopo Vivian: So these are the 2 points where you can find the air separator unit.
29:48:680Jacopo Vivian: Okay?
29:49:990Jacopo Vivian: Which?
29:52:80Jacopo Vivian: Why? Because in these points the solubility
29:57:290Jacopo Vivian: is the lowest. So it is easier for the air separator to work and remove the air.
30:04:840Jacopo Vivian: Okay, so
30:11:210Jacopo Vivian: we can. We can finish tomorrow and
30:15:490Jacopo Vivian: and then we will start the new topic.
30:19:60Jacopo Vivian: That's it for today.