MVHR with adiabatic cooling

[NSS]

9 hours ago, jack said:

 

Following on from my earlier comment about being surprised that it wasn't sweltering upstairs the night before last, I had the same experience last night. Back-to-back hottest days on record after a week of high and increasing temperatues, and it was still only a bit warm upstairs. Perfectly comfortable to sleep with a pedestal fan on low.

 

I can only assume that by getting the underfloor cooling on early and leaving it running 24 hours a day for the last handful of days, the temperature upstairs hasn't had a chance to get out of control. It's a puzzlement. 

We've just arrived home from 4 days away. Left the underfloor cooling running for the four hour cheap Octopus Go rate in the middle if the night and between 10am and 6pm (when PV covers almost all the energy needed to run it). Left the MVHR in auto (fan speed 1 8am-8pm and FS2 8pm to 8am). Downstairs stayed between 22C and 23C throughout and upstairs (no cooling on) was at 24.5c when we arrived home at noon today.

[Dan F]

9 hours ago, jack said:

 

Following on from my earlier comment about being surprised that it wasn't sweltering upstairs the night before last, I had the same experience last night. Back-to-back hottest days on record after a week of high and increasing temperatues, and it was still only a bit warm upstairs. Perfectly comfortable to sleep with a pedestal fan on low.

 

I can only assume that by getting the underfloor cooling on early and leaving it running 24 hours a day for the last handful of days, the temperature upstairs hasn't had a chance to get out of control. It's a puzzlement. 

 

Interesting. Did you reduce MVHR fan speed when it was very hot outside?  What (I think) I saw was that unless I turned on Comfopost or reduced MVHR to minumum, then the MVHR supply alone (which got up to around 26C) was gradually heating up the first floor.

 

 

 

 

[jack]

3 hours ago, Dan F said:

 

Interesting. Did you reduce MVHR fan speed when it was very hot outside?  What (I think) I saw was that unless I turned on Comfopost or reduced MVHR to minumum, then the MVHR supply alone (which got up to around 26C) was gradually heating up the first floor.

 

I generally run the MVHR at a fairly low default setting (80 or 100 m3 per hour, from memory) all year round.

[Dan F]

2 hours ago, jack said:

I generally run the MVHR at a fairly low default setting (80 or 100 m3 per hour, from memory) all year round.

 

Our "medium" (default) setting is 270m3/h, so no wonder we were seeing FF temperature gradually rise more than you even with blinds down. I dealt with this via running the comfopost a fair bit, but in hindsight I probably could have just turned the MVHR down.  This also may have reduced need for GF cooling too (Comfopost if FF only).  Our low setting is still 210m3/h, so I might even try away (62m3/h) if there isn't much cooking/showering.

Edited July 21, 2022 by Dan F
spelling

[SteamyTea]

5 hours ago, Dan F said:

 

Our "medium" (default) setting is 270m3/h, so no wonder we were seeing FF temperature gradually rise more than you even with blinds down. I dealt with this via running the comfopost a fair bit, but in hindsight I probably could have just turned the MVHR down.  This also may have reduced need for GF cooling too (Comfopost if FF only).  Our low setting is still 210m3/h, so I might even try away (62m3/h) if there isn't much cooking/showering.

What is the volume of your house?

That is what really sets the flow rate.

[jack]

7 hours ago, Dan F said:

Our "medium" (default) setting is 270m3/h, so no wonder we were seeing FF temperature gradually rise more than you even with blinds down. 

 

That seems high. Was that the building regs calculation?

 

Our house is 289 m² (with 2.85 m ceilings downstairs, a double height area, and 2.5 m ceilings upstairs, so probably higher volume than average for the floor area) and I think the BR calculation was 180 m³/h.

 

In general, the BR requirements ventilation rate is far too high imo. I know that several people on BuildHub have cut that rate by half (or more) without any issues. 

[Dan F]

3 hours ago, jack said:

 

That seems high. Was that the building regs calculation?

 

Our house is 289 m² (with 2.85 m ceilings downstairs, a double height area, and 2.5 m ceilings upstairs, so probably higher volume than average for the floor area) and I think the BR calculation was 180 m³/h.

 

In general, the BR requirements ventilation rate is far too high imo. I know that several people on BuildHub have cut that rate by half (or more) without any issues. 

 

Our design flow rate is actually 285m3 for some reason, not sure where they got this from!

 

We are 315m2, but ceiling is 2.5m downstairs and 2.4m upstairs making the total volume 780m3 (excluding loft).  If you average you room heights, your volume seems to be around 775m3, so almost excactly the same!  Building regaulations requirement would be 340m3h based on area for our house (or 310m3/h in your case).  Passive house guidelines give 230m3 for of us (300m3/h boost and 120m3/h miniumum),

 

So, looks like it makes sense to reconfigure ours to use the passive house numbers, and then (once I get the Loxone integration working) use the low setting more often e.g. when we are out.

 

Edited July 21, 2022 by Dan F