ᐅ Challenges for MEP planners: underfloor heating flow temperature and wastewater ventilation
Created on: 15 Jul 2022 10:22
P
Pacmansh
Hello,
we are at the beginning of the construction phase for our development project with the builder, and I am having some disagreements with the MEP planner. To be better prepared for the discussion, I would appreciate your assessment.
Point 1) Supply temperature of underfloor heating, new building, KfW55 standard, air-to-water heat pump
The supply temperature of the underfloor heating (end-terrace house on both floors) was stated to me as 40°C (104°F) after inquiry. This seems absurdly high to me. Additionally, I was informed that the surface temperature is designed to a maximum of 27°C (81°F) due to the flooring materials. Somehow, this does not seem consistent. When I asked about lowering the supply temperature, the response was: "A general reduction is not feasible with the underfloor heating without reducing the pipe spacing to an unacceptable level."
Do you have any ideas how I can respond to this in a reasonably professional way? Are there any documents or sources I could refer to, or information I should request?
Point 2) Wastewater venting
Contrary to earlier agreements, this has been planned in a rather unfavorable location. The reason given is "because the wastewater vent and the residential ventilation (exhaust air) must be routed over the roof with a certain separation according to flat roof guidelines." What distance should be maintained here? A quick online search only showed a 30cm (12 inches) distance to other building components. Basically, this is about the roof penetrations and their distance from each other, correct?
we are at the beginning of the construction phase for our development project with the builder, and I am having some disagreements with the MEP planner. To be better prepared for the discussion, I would appreciate your assessment.
Point 1) Supply temperature of underfloor heating, new building, KfW55 standard, air-to-water heat pump
The supply temperature of the underfloor heating (end-terrace house on both floors) was stated to me as 40°C (104°F) after inquiry. This seems absurdly high to me. Additionally, I was informed that the surface temperature is designed to a maximum of 27°C (81°F) due to the flooring materials. Somehow, this does not seem consistent. When I asked about lowering the supply temperature, the response was: "A general reduction is not feasible with the underfloor heating without reducing the pipe spacing to an unacceptable level."
Do you have any ideas how I can respond to this in a reasonably professional way? Are there any documents or sources I could refer to, or information I should request?
Point 2) Wastewater venting
Contrary to earlier agreements, this has been planned in a rather unfavorable location. The reason given is "because the wastewater vent and the residential ventilation (exhaust air) must be routed over the roof with a certain separation according to flat roof guidelines." What distance should be maintained here? A quick online search only showed a 30cm (12 inches) distance to other building components. Basically, this is about the roof penetrations and their distance from each other, correct?
Yes, the ventilation issue should definitely be questioned.
I hope it doesn’t add up to that, as that would be really bad.
But even so, you need to be aware that this heating load is not very good for a house of this size. I’m not as deep into this topic anymore, since it’s been a while for me. However, I would question the heating load again. Often, it is set too high, which then leads to a design requiring high supply temperatures.
There is a freely accessible tool available if you enter the words Crink and Tool in the well-known search engine. Once you have some basic input data, you can get quite far. Use it to compare if it matches the assumptions used here. If it does, in my opinion, you won’t end up with a design at 30 degrees Celsius (86°F)… but something better than 40 degrees Celsius (104°F) should be possible.
I hope it doesn’t add up to that, as that would be really bad.
But even so, you need to be aware that this heating load is not very good for a house of this size. I’m not as deep into this topic anymore, since it’s been a while for me. However, I would question the heating load again. Often, it is set too high, which then leads to a design requiring high supply temperatures.
There is a freely accessible tool available if you enter the words Crink and Tool in the well-known search engine. Once you have some basic input data, you can get quite far. Use it to compare if it matches the assumptions used here. If it does, in my opinion, you won’t end up with a design at 30 degrees Celsius (86°F)… but something better than 40 degrees Celsius (104°F) should be possible.
RotorMotor schrieb:
The last column is unclear. Are these ventilation heat losses (which doesn’t make much sense, since some rooms are missing) or is it the exchange between rooms (the hallway is missing there as well)...? I calculated the last column myself. I have a document that lists the supply and exhaust air. Supply air is only provided through the specified rooms and, as I understand it, is heated there. The bathrooms are missing, that’s correct. The hallway only has supply air at room temperature, so I left it out.
RotorMotor schrieb:
That indicates the pressure loss. That then depends on the length if the duct diameter is the same (I noticed I still transferred some data incorrectly for the pressure loss on the ground floor). Accordingly, in the current layout, I should at least divide room 15.06 with 171 mbar (millibar) into two circuits and possibly also split the bathroom into two circuits so that the difference is not so large.
face26 schrieb:
Often it is the case that this is set too high, which then results in a design with high supply temperatures. Unfortunately, I lack data on the U-value, so I can’t calculate it with the tool. But how is it that the tool assumes a standard outdoor temperature of -11.3° Celsius (11.3°F) for my location, while my planner uses -14° (or -16°, I still need to ask) Celsius (7°F or 3.2°F)?
It is probably true that the heating load for such a building is very high. I was hoping for a bit less myself. However, the ventilation obviously also has a significant impact. Financially, though, it wasn’t feasible otherwise. A controlled residential ventilation system with heat recovery would have added well over €20,000 in extra costs and would have been planned by the same designer whom I already didn’t trust at the start.
Pacmansh schrieb:
Unfortunately, I don’t have data on the U-value, so I can’t calculate it using the tool. But why does the tool assume a standard outdoor temperature of -11.3°C (12°F) for my location, while my planner uses -14°C (7°F) or even -16°C (3°F)? I need to check that again. Then have them provide it to you. The data must be included in the energy performance certificate anyway, so it’s not a secret.
Phew, as I said, this was two years ago for me, but I believe that about three years ago the official standard outdoor temperature values were updated and refined. These are the values used for official calculations like government energy subsidies and so on. You can find a lot by searching online. There is apparently a site from an association where you can enter the postal code, and it shows the official standard temperature.
The “old” temperatures were significantly lower. It sounds to me like the older values were used in your case. Basically, “safety margins” are often included in calculations to prevent complaints later on.
However, this results in a higher heating demand, then without ventilation and probably with a U-value leaning more toward the minimum required by energy regulations rather than the “55 standard,” so you end up with these kinds of specifications...
Thank you for the note. I have now found it. The temperature of -11.3°C (12°F) is correct here, but how should this be interpreted? Is the planner not following the current standard? Is it still allowed to use the old values? The contract states: "The heating system will be designed for the coldest day according to the standard...".
Now, regarding practical use:
Wouldn't it simply be a matter of setting a lower flow temperature than the calculated one after moving in? The temperature balance between rooms shouldn't vary too much. Of course, it would make a difference if a smaller heat pump could be installed due to the lower heating load. Or am I thinking too simply here?
Now, regarding practical use:
Wouldn't it simply be a matter of setting a lower flow temperature than the calculated one after moving in? The temperature balance between rooms shouldn't vary too much. Of course, it would make a difference if a smaller heat pump could be installed due to the lower heating load. Or am I thinking too simply here?
I’m not familiar with the legal aspects. Essentially, you’re right—if that’s actually the case.
However, many people say pragmatically that you don’t need to calculate so much. Just use a 10cm (4 inches) installation spacing everywhere, 5cm (2 inches) in the bathrooms, and avoid loops that are too long or of uneven length.
Has this been mentioned here already? Which heat pump will be installed? Oversizing is not just a problem because it might be expensive, but also because the heat pump could start short-cycling, which reduces efficiency.
However, many people say pragmatically that you don’t need to calculate so much. Just use a 10cm (4 inches) installation spacing everywhere, 5cm (2 inches) in the bathrooms, and avoid loops that are too long or of uneven length.
Has this been mentioned here already? Which heat pump will be installed? Oversizing is not just a problem because it might be expensive, but also because the heat pump could start short-cycling, which reduces efficiency.
I find the entire approach of the planners to be audacious and unprofessional. But since you’re bound by it, you have to accept it.
Of course, you can and should still perform a thermal balancing afterward and correctly adjust the heating curve. Usually, the heating installer just sets it to “as long as it gets warm.”
Of course, you can and should still perform a thermal balancing afterward and correctly adjust the heating curve. Usually, the heating installer just sets it to “as long as it gets warm.”
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