MVHR with active cooling

[Dan F]

1 minute ago, Levo said:

> I am not familiar with Comfopost, just looked up the Specific Heat Capacity of Air and based my calculation on that but your example seem to use the same 15C delta as I used. I also checked one of the 2.5KW Fujitsu Split air cons and they quote 700m3/h fan rates. Even if they didn't need the full 700m3/h and only needed 4-500m3/h to achieve 2.5KW cooling, you will likely achieve only a fraction of the 1.9KW @140m3/h, I think.

 

I copied the value from the datasheet.  It is more complex because there is also "sensible power" with cooling due to condensation, so that might explain the difference.

 

1 minute ago, Levo said:

 

>I have a 1970s house and not one of them passive houses?. So, I personally satisfied myself that the MVHR at 100-150M3/h rates will not make any dent either on heating or cooling my house.

 

Agree!

 

[SteamyTea]

8 hours ago, Dan F said:

It is more complex because there is also "sensible power" with cooling due to condensation, so that might explain the difference.

Isn't that latent heat?

[troggy02]

On 27/10/2020 at 21:28, Levo said:

>That was a heating example; i.e. whether the heat recouped from a Bathroom and/or kitchen would help any. I tend to blast the bathroom with an electric fan to warm up before shower. Never actually checked what temp, so assumed it would be 8C higher than the normal room temp in the house.

 

> I am not familiar with Comfopost, just looked up the Specific Heat Capacity of Air and based my calculation on that but your example seem to use the same 15C delta as I used. I also checked one of the 2.5KW Fujitsu Split air cons and they quote 700m3/h fan rates. Even if they didn't need the full 700m3/h and only needed 4-500m3/h to achieve 2.5KW cooling, you will likely achieve only a fraction of the 1.9KW @140m3/h, I think.

 

>I have a 1970s house and not one of them passive houses?. So, I personally satisfied myself that the MVHR at 100-150M3/h rates will not make any dent either on heating or cooling my house.

 

Just a word of caution on air source heat pumps, I know they are improving every year but no matter what the manufacturers say, their pumping capacity degrades the closer you get to 0C and go below. I have some friends with Air sourced UFH  in the south of England who live in a reasonably new (~5 year old) property and complain the house doesn't warm up on cold nights.

 

We have a large well insulated house and 18kW capacity ASHP and the house is toasty warm at -7c (last winter). I'd suggest your friends system in improperly installed or spec'd in some way. 

[Adsibob]

On 13/08/2020 at 17:37, Bitpipe said:

We keep our passive house cool by doing stack ventilation at night

Any tips for doing this? I have two Veluxes that are both East facing and then regular windows in each room on the opposite side of the house (West facing). I open all of these at around 8pm and it definitely cools the top floor. Should I also open windows in the middle floor (my house has three floors, including GF), or will MVHR be enough?

 And at what time do you close the windows? I wish i’d installed veluxes on both sides of the roof, not just one! 
Would investing in velux’s automation Velux Active help at all, or will it not help because the draft i need will only work if I open the windows on the west side of the top floor, and that can’t be automated?

i also have a small window on the South side of the house at top floor level, if that is relevant at all.

[Adam2]

It may be preferable to have low and high windows/rooflights to develop a chimney effect with the overheated air rising out the top causing (hopefully) cooler air to be sucked in from lower down and drawn up through the house. Well that's at least my plan but not quite yet moved in so will not be able to experiment just yet! Alternatively if you have a through flow of course that could work depending on wind but I really like the chimney idea as that seems like it should work regardless of wind