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?
R
RotorMotor14 Oct 2022 09:49face26 schrieb:
I understand the approach. I didn’t pay attention to whether the OP has ventilation (or you @RotorMotor), but with ventilation, moisture shouldn’t be a problem.We have a central controlled residential ventilation system, but unfortunately that’s not enough for the bathroom. Humidity rarely drops below 70% there at the moment. The air-to-water heat pump simply isn’t running often enough yet, and when it does, currently with a supply temperature of 25°C (77°F) and an air temperature of 24°C (75°F) in the bathroom, that’s a delta T of only one degree, so the heat pump is practically not heating at all right now while moisture is constantly being introduced by showering.face26 schrieb:
And I don’t know what kind of kW monsters you have for towel radiators, but usually they don’t provide much heating power, and if they do, they consume a lot.300W.face26 schrieb:
Hopefully you don’t really believe your last sentence about free photovoltaic electricity!? :p
That costs you at least the feed-in tariff.Actually, I know that quite well. Because of KFW40Plus, I have a 60% curtailment. The 300W from the radiators fit perfectly into the free 40% curtailed portion through KNX, which would otherwise be unused. 😉 But okay, that’s probably only the case for few people.face26 schrieb:
… and in winter, the electricity from the photovoltaic system (if any) is already consumed by your heat pump or base load.That’s correct, but then the heat pump also provides enough heat to our bathrooms thanks to a fully covered wall. However, as mentioned above, currently with a delta T of 1 degree, it doesn’t help at all.
RotorMotor schrieb:
We have a central controlled ventilation system, but unfortunately, it’s not sufficient for the bathroom.
The humidity rarely drops below 70% at the moment. The air-to-water heat pump simply doesn’t run often enough yet and when it does, currently at a 25°C (77°F) supply temperature with 24°C (75°F) air temperature in the bathroom, that’s a delta T of one degree, so basically the heat pump isn’t providing any heating right now, while moisture is constantly added from showering. Then you must have a poorly designed controlled ventilation system; this is not related to the heating behavior of your heat pump.
Regarding the rest...
We don’t have the KFW40Plus standard combined with KNX here, and probably this isn’t common elsewhere either.
As I understand it, you only use the towel radiators during the transitional seasons because usually (in winter) you have sufficient heating capacity.
Which, for the original poster, would not be the case if they want to lower the supply temperature.
In my opinion, electric towel warmers remain (with exceptions, of course, @RotorMotor) a nice gimmick for someone who wants warm towels or quicker drying. I wouldn’t plan them as part of the main heating capacity, especially since they tend to be somewhat slow to respond.
For the case of the original poster, who probably faces insufficient heating power in the bathroom when lowering the supply temperature, it makes the most sense to have a quickly available heating source temporarily. I find fan heaters a very simple solution for that.
Depending on personal preference, infrared panels or similar options could also work.
That certainly sounds like a very good and well-thought-out solution. With a bit more budget and a plot of land, I would have gladly done it that way myself. 😉
As for us, we have ventilation installed. How well it works with towel drying, humidity in the bathroom, and so on, I guess I'll just have to find out by experience. Since towel warmers are included in the scope of work for both bathrooms, there is definitely no reason not to have them installed. At worst, we’ll just treat ourselves to the luxury of pre-warmed towels.
However, I’m also skeptical about the idea of preparing a wall heating system. I haven’t met the plumber yet and will probably only be able to decide after the heating pipes have been laid. An inspector appointment for this has already been scheduled. We will examine everything in detail then.
As for us, we have ventilation installed. How well it works with towel drying, humidity in the bathroom, and so on, I guess I'll just have to find out by experience. Since towel warmers are included in the scope of work for both bathrooms, there is definitely no reason not to have them installed. At worst, we’ll just treat ourselves to the luxury of pre-warmed towels.
However, I’m also skeptical about the idea of preparing a wall heating system. I haven’t met the plumber yet and will probably only be able to decide after the heating pipes have been laid. An inspector appointment for this has already been scheduled. We will examine everything in detail then.
I would definitely have more pipes installed there and reduce the spacing... use the smallest possible stainless steel pipe in the bathroom.
24°C (75°F) in the bathroom is also quite excessive, especially if adjacent rooms are cooler; it will only work to a limited extent. If underfloor heating is no longer an option, still try to get the supply line as close as possible to 30°C (86°F), whether for gas or heat pump systems. Both will benefit you in the long run, and right now you still have the chance to push for this persistently—it’s your house and your money.
24°C (75°F) in the bathroom is also quite excessive, especially if adjacent rooms are cooler; it will only work to a limited extent. If underfloor heating is no longer an option, still try to get the supply line as close as possible to 30°C (86°F), whether for gas or heat pump systems. Both will benefit you in the long run, and right now you still have the chance to push for this persistently—it’s your house and your money.
I don’t think the house can handle that. I already managed to reduce it from 40°C (104°F) to 36°C (97°F), and the pipe spacing in the bathrooms is 5cm (2 inches). Of course, I could lower the design temperature in the bathrooms to 20°C (68°F), which might reduce the calculated supply temperature. But in the end, that doesn’t really result in any real benefit.
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SaniererNRW12314 Oct 2022 10:33Pacmansh schrieb:
I don’t think the house can handle that. I managed to reduce it from 40°C (104°F) to 36°C (97°F), and the spacing for the pipes in the bathrooms is 5cm (2 inches).EVERY new build operates at 30 degrees supply temperature. A heating engineer may say this is not possible—but that’s usually just because they don't want to deal with it.