UFH to help cooling?

[NSS]

30 minutes ago, JohnMo said:

Aren't you better to run the MVHR at the normal speed. Then the MVHR actively pulls the humidity out the house, moving dew point upwards.

Possibly, but it's a case of six or two threes. Temp at 8pm yesterday when it would normally switch to night mode was still 30c, and was 27c when I went to bed at 11.30pm. I decided there was no point pulling in air that was going to need cooling.

[NSS]

3 minutes ago, jack said:

 

Generally yes, but only if humidity is lower outside than in.

Where I am, humidity is still high, and is forecast to rise through the night into the high 80s. Thankfully it should drop a fair bit through tomorrow.

 

Here too. We're only a mile from the Solent, so external humidity is generally higher.

[marshian]

Interesting topic - Heat Geek have just released a video on the subject and there was one thing that got my attention bearing in mind I am all rads (no UFH) and they are almost all converted to TBOE from a flow perspective - I will one day convert to heat pump but when the boiler dies or Gas v Electricity cost perspective drives the change.

 

Anyway here it is 
 

 

 

[richo106]

I have just been looking at mine again, with water temp of 16/17deg there is a tiny bit of moisture on the manifold downstairs - temp 25.4 and humidity 47% ( around 10% higher than normal) gives a dew point of 13.3 deg so not concerned downstairs 

 

upstairs is around 28 degs and 57% humidity so has a decent amount of condensation on the manifold as dew point 18.3 deg. Upstairs is mainly carpets except tiled bathroom but tbh the ufh is pretty ineffective upstairs so not concerned however I have just turned the manifold valves off. Unfortunately I have no way of isolating the flow and return pipes to u/s manifold but pipes are lagged in the ceiling 

 

Does anyone see any issues here?

 

I am new to using ufh/ASHP for cooling but it certainly makes a difference downstairs and a lot more humid than usual 

[-rick-]

21 hours ago, richo106 said:

I have been looking into but has anyone successfully cooled the supply air for a MVHR system? I am not after AC like performance but just something to take the edge off on the really hot days

I think it’s well established that a hydronic heat exchanger in line with the MHVR doesn’t really have the oomph for real heating and cooling.

 

I’d always thought to add a smallish one anyway with the hope of maybe bringing the mhvr output air temp above/below* the ambient internal temp vs just below/above* due to mhvr efficiency. Thinking being that not every room would be exposed to ufh so the mhvr coil would just help distribute the heat/cool more widely (Wouldn’t even think about it if couldn’t find a suitable cheap coil)

 

This thread has made me wonder if that coil might have a useful dehumidifier aspect during heatwaves like this. If you are running the flow temp low enough to cause condensation on the floor then inevitably the exposed coils in the heat exchanger would be cooler than the floor and attract more condensation. If running only a touch below dew point then maybe the excess moisture preferentially condenses in the mhvr coil and prevents condensate forming on the floors. So not full bore dehumidification but just enough to allow you to lower the floor temp a degree or two more than you otherwise would.

 

Does this stand up to reality?

 

* depending on whether you are heating or cooling (in that order)

[JohnMo]

1 hour ago, -rick- said:

thread has made me wonder if that coil might have a useful dehumidifier aspect during heatwaves like this.

I was thinking about this last night also. A coil upstream of the MVHR unit (outside to MVHR leg) would cool the air and cause condensation which would reduce the moisture carried by the air. Condensation would be cleared away by MVHR drain or drain within heat exchanger. As outside air travels through heat exchanger it is then heated by house air temperature, diving RH to a happier place. Then run MVHR as normal and get lower internal humidity and more dew point safety margin.

[jack]

5 minutes ago, JohnMo said:

I was thinking about this last night also. A coil upstream of the MVHR unit (outside to MVHR leg) would cool the air and cause condensation which would reduce the moisture carried by the air. Condensation would be cleared away by MVHR drain or drain within heat exchanger. As outside air travels through heat exchanger it is then heated by house air temperature, diving RH to a happier place. Then run MVHR as normal and get lower internal humidity and more dew point safety margin.

 

Any particular reason to place this upstream of the MVHR unit?

 

I may be missing something, but this way you'd lose some of the "coolth" through heat exchanger inefficiency. That inefficiency could potentially be worsened by moisture in the outgoing air condensing due to the cold incoming air.

 

[-rick-]

57 minutes ago, jack said:

I may be missing something, but this way you'd lose some of the "coolth" through heat exchanger inefficiency. That inefficiency could potentially be worsened by moisture in the outgoing air condensing due to the cold incoming air.

 

Agree with that thought.

 

let the mhvr do the bulk to the dehumidification for free. The coil just does the top off. It means the temp difference between the water and air will be lower so less effective. But there’s no way near dew point water will be able to suck much out of the air but even a small amount might be enough.

[JohnMo]

2 hours ago, jack said:

 

Any particular reason to place this upstream of the MVHR unit?

 

I may be missing something, but this way you'd lose some of the "coolth" through heat exchanger inefficiency. That inefficiency could potentially be worsened by moisture in the outgoing air condensing due to the cold incoming air.

 

Yes. MVHR and actual cooling ability is pretty rubbish as flow rates are small.

 

I was talking about management of humidity margin in cooling, so the RH is actually lowered by the MVHR. Having the unit upstream of heat exchanger cools the air and causes it condense, then it's reheated by the outgoing house air via the heat exchanger changing the RH. Net effect is lower RH when compared to outside air.

 

One of the issues in winter with MVHR is it lowers the humidity levels too much with prolonged cold outside temperatures, you are just duplicating those effects to your advantage.

[-rick-]

7 minutes ago, JohnMo said:

I was talking about management of humidity margin in cooling, so the RH is actually lowered by the MVHR. Having the unit upstream of heat exchanger cools the air and causes it condense, then it's reheated by the outgoing house air via the heat exchanger changing the RH. Net effect is lower RH when compared to outside air.

hopefully someone has the time to do the maths or get Ai to do it. But my guess is that water at 15-16C has nowhere near enough potential cooling in it to strip the humidity out of incoming humid air before the MHVR. (Dehumidifying humid air uses a similar amount of energy to cooling it). The MHVR can do effective bulk dehumidification but only to a limit. So my thought is let it do that for free then use the coils to take a bit more off the top once the MHVR has done as much as it can.

[JohnMo]

1 hour ago, -rick- said:

But my guess is that water at 15-16C has nowhere near enough potential cooling in it to strip the humidity out of incoming humid air before the MHVR. (Dehumidifying humid air uses a similar amount of energy to cooling it). The MHVR can do effective bulk dehumidification but only to a limit. So my thought is let it do that for free then use the coils to take a bit more off the top once the MHVR has done as much as it can.

Think we are in the same ball park. Its just playing with dew points at different places in the system. The additional cooling adds an few extra degree of dew point movement. The additional HE can be anywhere in the system really, the outcome pretty similar. The energy in/out equation and dew point effect still gives the same answer. Adding the additional HE can work in summer and winter. Cooling and heating effect pretty small a few watts per m² but steps in the correct direction.