AI Assistant
Transcript
00:01:510Jacopo Vivian: Oh, pretty good.
00:54:560Jacopo Vivian: Okay. Welcome everyone. Sorry for the slight delay due to
00:59:980Jacopo Vivian: some technical issues. But now it should work.
01:05:390Jacopo Vivian: You have all the slides on Moodle also for next lectures. So
01:12:636Jacopo Vivian: I hope you can download the you could download the Pdfs.
01:18:400Jacopo Vivian: I start from where we left. Last week
01:22:80Jacopo Vivian: we started looking at layouts of hydronic systems, namely, systems that use water as heat carrier fluid for as
01:33:620Jacopo Vivian: space heating space, cooling and domestic hot water production. These are the end uses we are talking about in this course.
01:43:700Jacopo Vivian: So we have seen the single pipe, this single pipe system.
01:51:270Jacopo Vivian: We have seen the single pipe system with the
01:56:854Jacopo Vivian: parallel connection of the terminal units.
02:00:730Jacopo Vivian: We have seen the 2 pipe system with a direct return.
02:06:470Jacopo Vivian: And today we talk about another system, which is a
02:13:300Jacopo Vivian: the 2 pipe system with reverse return.
02:17:870Jacopo Vivian: What do we mean by reverse return.
02:21:120Jacopo Vivian: if you remember, from last week I draw on the on the blackboard a diagram that
02:30:440Jacopo Vivian: giving us the pressure in each point of the circuit
02:34:660Jacopo Vivian: as a function of the distance to the main pump or to the generation unit.
02:42:130Jacopo Vivian: If you remember, we have a kind of a cone distribution of the pressures
02:49:20Jacopo Vivian: the far we go far away from the generation. The lower is the pressure difference between
02:57:920Jacopo Vivian: the supply and the return to each terminal unit.
03:02:150Jacopo Vivian: Okay, that means that in normal normal operation with the direct return, we have more flow
03:17:490Jacopo Vivian: to the closer to the, to the terminal units that are closest to the generation.
03:23:570Jacopo Vivian: Okay? Because the pressure differential between.
03:28:500Jacopo Vivian: That's me.
03:33:870Jacopo Vivian: Use the pointer between this point here and this point
03:41:560Jacopo Vivian: is higher than the pressure differential between this point and this point.
03:48:830Jacopo Vivian: Okay, this is a consequence of
03:53:390Jacopo Vivian: continuous and localized pressure losses along the distribution lines.
04:01:450Jacopo Vivian: So that means, if we don't do anything to regulate the system we expect to have
04:11:900Jacopo Vivian: given that these we assume. These radiators are the same. So they have the same hydraulic resistance. Okay.
04:22:180Jacopo Vivian: so we assume that the 1st radiator will have a higher flow
04:28:280Jacopo Vivian: circulating through it compared to the last radiator.
04:32:740Jacopo Vivian: Okay.
04:34:830Jacopo Vivian: so we will see there are ways to prevent this problem. But one way is already at the design stage of the distribution system.
04:45:420Jacopo Vivian: and the way is to have that the reverse return, meaning that the 1st supply. The
04:59:840Jacopo Vivian: the return line does not start from the first, st but from the last supply unit.
05:08:930Jacopo Vivian: Okay, I don't like this scheme very much. I don't think it is
05:16:874Jacopo Vivian: very clear. So I also included the other schemes.
05:21:580Jacopo Vivian: But basically the reverse return system is, it
05:28:610Jacopo Vivian: has disadvantage over the direct return that it is able to self balance the system.
05:37:360Jacopo Vivian: because the last terminal unit imagine the last radiator in the previous
05:43:150Jacopo Vivian: scheme is hydraulically the closest to the pump on the return line.
05:49:800Jacopo Vivian: and of course we have a higher cost.
05:54:850Jacopo Vivian: although it is not very clear from this drawing, but we can see it here.
05:59:750Jacopo Vivian: Okay, in the, as you can see, the Delta. P. Here is it
06:09:460Jacopo Vivian: more similar between the terminal units compared to the direct return?
06:15:440Jacopo Vivian: Because in the 1st terminal unit.
06:19:50Jacopo Vivian: okay, we are hydraulically very close to the generation or to the main pump here on the supply line.
06:27:560Jacopo Vivian: But we are far away. If you look at the return line, you see, the flow has to
06:35:880Jacopo Vivian: go all the way through this distribution line, and then back, and the the farther we go.
06:45:850Jacopo Vivian: the lower the the way that the flow has to
06:53:520Jacopo Vivian: do to reach the return of the generation unit.
06:58:510Jacopo Vivian: So if you go to the last terminal unit, you see, it is very far away from the generation unit from the supply point of view.
07:08:140Jacopo Vivian: But it is the closest to the generation from the return point of view.
07:15:320Jacopo Vivian: And why is the disadvantage about the cost, because look at the return line before we only had
07:26:480Jacopo Vivian: one pipe.
07:28:290Jacopo Vivian: But here you have one and 2.
07:32:890Jacopo Vivian: Okay, so basically, we have a
07:36:740Jacopo Vivian: in this. In this case, 50% more of the length of pipes
07:43:30Jacopo Vivian: compared to the direct return. Because basically, we are doubling the return line
07:49:940Jacopo Vivian: here. I think this is the
07:53:460Jacopo Vivian: best drawing to understand the concept.
07:57:250Jacopo Vivian: But on the right you you can see that we can also balance in case we have a heat supply station. Imagine a condominium, a very large condominium, and we have risers that are one is on the practically very close to the heat supply station on the same side of the building.
08:19:70Jacopo Vivian: and then we have maybe I don't know 50 meters of horizontal distribution to reach the second riser.
08:29:70Jacopo Vivian: Okay, in this case
08:31:790Jacopo Vivian: we can use the the reverse. Return to balance the 2 risers without introducing something that we will see later on in the in the course this week, which are balancing valves.
08:46:120Jacopo Vivian: In this way we balance the Delta P between the 2 risers.
08:51:256Jacopo Vivian: By simply using the reverse return on the horizontal distribution.
08:59:370Jacopo Vivian: Of course, of course, you can also use the reverse return on each individual radiator.
09:09:30Jacopo Vivian: Okay, so for each riser you can have the reverse return. You can see here.
09:15:820Jacopo Vivian: but of course this means that we are
09:18:810Jacopo Vivian: in this case we balance the Delta P between the the radiators of each riser of each riser. But in this case, of course, we have.
09:29:130Jacopo Vivian: and a further increase in costs.
09:33:520Jacopo Vivian: because we have. We don't only double the return line on the horizontal distribution.
09:40:730Jacopo Vivian: We also double all the return lines on the risers. So instead of having
09:47:740Jacopo Vivian: 2 pipes, we have 3 pipes for each riser, yes, but in the physical distribution you were able to
10:00:770Jacopo Vivian: move to the 25.
10:02:770Jacopo Vivian: Yes, on the in this case, that
10:07:466Jacopo Vivian: this is why it's called reverse return because you only work on the return line. So the 1st
10:18:140Jacopo Vivian: I, if I understand your question.
10:22:210Jacopo Vivian: we still have the 1st radiator to be the closest to the generation, and the last one to be the farthest away from the supply line.
10:31:790Jacopo Vivian: It's just reversed on the return line.
10:35:40Jacopo Vivian: Was that your question? Or I said so. One of the goals is that the last category?
10:44:630Jacopo Vivian: It closes to the password on the reservation?
10:47:760Jacopo Vivian: Yes, yes, because the last 10 will do the one that's
10:57:410Jacopo Vivian: here we are. You can see the 2 columns. So the 2 risers as a 2 terminal unit.
11:05:570Jacopo Vivian: or in this way we say.
11:09:244Jacopo Vivian: If so, what I I said my example was, if the length between this point and this point here is a lot.
11:20:550Jacopo Vivian: then you might have the Delta P problem. So, for example, the Delta P of the column, one would be much bigger than the Delta P. Between column between the 2 points, connection points of riser? 2.
11:36:730Jacopo Vivian: So in this case we can have the direct, the reverse return only in the horizontal distribution.
11:44:680Jacopo Vivian: Okay, so talk to. So what you said, is, actually.
11:52:40Jacopo Vivian: we can use the reverse the music only if the
11:57:750Jacopo Vivian: 2 license are close to each other.
12:00:930Jacopo Vivian: No, I say that it makes sense to use the reverse return only if
12:08:870Jacopo Vivian: the Delta P, due to the continuous and and localized pressure losses between this point and this point is very big, so if the risers are not close to each other.
12:21:830Jacopo Vivian: but if they are far away from each other.
12:24:390Jacopo Vivian: and please always think that when I say far away.
12:29:140Jacopo Vivian: I mean, because you know that from a hydraulic point of view
12:36:90Jacopo Vivian: the pressure losses are either continuous or or localized.
12:43:470Jacopo Vivian: And the
12:44:940Jacopo Vivian: if we always have continuous pressure pressure losses, and we know that they increase linearly with distance. This is why I say, far away.
12:56:70Jacopo Vivian: But of course you also need to account for localized pressure losses. So what I mean is,
13:05:990Jacopo Vivian: we don't only count here the 50 meters. Okay.
13:12:670Jacopo Vivian: but we also count the deviation, the curves, the bending the valves, and everything that will make the pressure drop between this point and this point. So when I say hydraulic, hydraulically distant, I mean not only from a
13:34:760Jacopo Vivian: space point of view, but also from a hydraulic point of view. Okay.
13:42:290Jacopo Vivian: so this is an example of reversal return on each single riser which would increase the cost. Of course.
13:51:150Jacopo Vivian: in this case it makes sense only if we need to balance from the design stage the delta P between the radiators or the terminal each
14:05:775Jacopo Vivian: initizure.
14:16:760Jacopo Vivian: I'm sorry, but in this room I need to use the old laptop and the old laptop crashes
14:25:920Jacopo Vivian: every time. So I hope for now that's the.