Why am I putting in an ashp in a passive house?

[Nickfromwales]

On 23/03/2024 at 22:37, CalvinHobbes said:

So why should I do it?

Cooling.

[Nick Laslett]

7 hours ago, Nickfromwales said:

Cooling.

My build is taking me forever, so I have no actual facts or data to share. When I first came to BuildHub and started this journey, the challenge of cooling kept on coming up. Insulation and an airtight build mitigated the heating requirements, but due to solar gain, how did you tackle cooling. PPHP modelling, window shading these were the go to advice. Actual air conditioning if you could accommodate it. Then in amongst all this talk you discover an ASHP can be run in reverse and provide cooling. Back in 2019 there was some debate about if this wasn’t allowed by RHI or MCS, some ASHPs didn’t allow cooling or had the feature locked. 
 

For me this sounded like a good cooling solution. I was going to build an ICF house and have a poured concrete 90mm thick 1st floor. So I installed wet UFH in the first floor expressly for the cooling. The concrete floor was now not just an extravagant way to have a solid, non-creaky, sound proof floor. It was now my cooling block for the bedrooms. 
 

Unfortunately, I’m still building so have no idea if this approach will work. I also went with 70/30 tinted glass on the windows to help with the solar gain. And I’m putting the cooling module on my MVHR, which doesn’t seem very popular or value for money, or even effective! 
 

So @Nickfromwales one word advice might seem a bit cryptic, but to me it is classic Buildhub. 
 

 

[Conor]

We find slab cooling with ASHP very effective, even if it's only needed once a year or so (in northern Ireland so daytime temps rarely in the high 20s and nighttime usually in low teens)

[JohnMo]

3 minutes ago, Conor said:

We find slab cooling with ASHP very effective, even if it's only needed once a year or so (in northern Ireland so daytime temps rarely in the high 20s and nighttime usually in low teens)

Us also. Not as good as Aircon, but does knock a couple of degrees off when needed. If you have PV generally free to use also.

[Stones]

I'd also suggest comfort comes into this, and what type of heat you want.  How an A2A delivers vs an A2W via UFH.   

 

I personally dislike warm air being blown around by an A2A, but when on holiday, appreciate the cool breeze of aircon. 

 

Heat delivered via UFH from our A2W gives a nice steady even temperature in house (with the added benefit A2W provides my DHW needs as well). But the cooling is less effective as it takes longer (albeit very pleasant when up (down?) to temperature.

 

I think A2A are fantastic in large rooms / open spaces, less so in small(er) rooms.

 

Like everything else, there are trade offs, and individual lifestyle requirements, and house location / design all play a part.

[Cooeyswell]

22 hours ago, Nickfromwales said:

Cooling.

As quoted by our representative from the sunny uplands of southern Wales.

I'm living in a Passive spec build in a northern land - cooling ain't an issue.

 

[Nickfromwales]

38 minutes ago, Cooeyswell said:

As quoted by our representative from the sunny uplands of southern Wales.

I'm living in a Passive spec build in a northern land - cooling ain't an issue.

 

A Passsive spec build? Please elaborate...

 

Depending on how far north, your PHPP may have specified that you wear thermal undercrackers.

[Nickfromwales]

15 hours ago, Nick Laslett said:

So @Nickfromwales one word advice might seem a bit cryptic, but to me it is classic Buildhub. 
 

I am a man of few words... until 2 pints go in and then you can't shut me up  

 

Give me a slightly cold home and I'll pop a blanket over me, but give me a warm house and I'll kill everyone within a 50m radius.

[joe90]

When I did my build I was told by many here that my south facing 10m conservatory with bifolds into the house would overheat but frankly in the several years I was there it never got hotter than a good holiday in the south of France, (which many pay good money for) and during the shoulder seasons and even mild winter days was a lovely place to be.

[Cooeyswell]

10 minutes ago, Nickfromwales said:

A Passsive spec build? Please elaborate...

 

Depending on how far north, your PHPP may have specified that you wear thermal undercrackers.

 

Passive spec- 0.1U-0.12uU in all directions, 0.15U windows, MVHR etc. The usual stuff.

 

I lived outside Chepstow for many years. At no point did I encounter Welsh cooling undercrackers, neither has anyone here suggested the application of Welsh crackers (under or over) as a cooling mechanism. I look forward to being enlightened.

[JohnMo]

8 hours ago, Cooeyswell said:

As quoted by our representative from the sunny uplands of southern Wales.

I'm living in a Passive spec build in a northern land - cooling ain't an issue.

 

I live at in NE Scotland and use cooling, the main reason for getting a heat pump was for cooling. Doesn't really matter where you live if you have biggish windows for the view, you will get over heating.

 

7 hours ago, joe90 said:

10m conservatory with bifolds into the house would overheat but frankly in the several years I was there it never got hotter than a good holiday

So about 30 degs?

[Nickfromwales]

8 hours ago, Cooeyswell said:

 

Passive spec- 0.1U-0.12uU in all directions, 0.15U windows, MVHR etc. The usual stuff.

 

I lived outside Chepstow for many years. At no point did I encounter Welsh cooling undercrackers, neither has anyone here suggested the application of Welsh crackers (under or over) as a cooling mechanism. I look forward to being enlightened.

Did your PH designer specify little windows and minimal southern glazing etc? Shading too? Most Passiv spec dwellings get very uncomfortable in the peak summer period.
I’m about to start a certified PH build for a client, and we identified early on (on paper) that, for at least 35 days of the year, it would be outside a survivable temperature for the residents (PHPP done) so absolutely couldn’t be built without cooling having being introduced by design; as a mitigating measure to demonstrate that this had been addressed.

PH architect suggested A2A A/C and also that the A/C got used to offset the opposite effect, where for 18 days (more imo) there would be a requirement for auxiliary heating. Suggestion was to pull out oil filled rads and heat the spaces independently to suit. Client found this out only after I highlighted it, and they weren’t very impressed. Lots of back-pedalling and talk of cross / purge ventilation and so on.

 

If you’re managing without mechanical cooling I am equally curious, but house location / orientation / shading et-al and the micro-climate all play very large roles so defo ‘possible’ to design this out (solar reflective glazing is another Ace to keep up one’s sleeve). 

[Iceverge]

On 25/03/2024 at 10:23, joth said:

Be very wary of those sort of claims: the people making them are often highly invested (financially and emotionally) to push the performance of their building. Also just because one PH building does not need active heating it means nothing for the next.

 

Yes. Been there done that. 

 

You need if you want  a warm house you need a heat source.

 

Perpetual energy machines don't exist. 

[Sparrowhawk]

8 hours ago, Nickfromwales said:

I’m about to start a certified PH build for a client, and we identified early on (on paper) that, for at least 35 days of the year, it would be outside a survivable temperature for the residents (PHPP done) so absolutely couldn’t be built without cooling having being introduced by design; as a mitigating measure to demonstrate that this had been addressed.

PH architect suggested A2A A/C and also that the A/C got used to offset the opposite effect, where for 18 days (more imo) there would be a requirement for auxiliary heating. Suggestion was to pull out oil filled rads and heat the spaces independently to suit. Client found this out only after I highlighted it, and they weren’t very impressed. Lots of back-pedalling and talk of cross / purge ventilation and so on.

Sounds like this PH architect has designed to the letter of the certification and not to the spirit. Unless the clients have imposed limitations that make it impossible to design out the overheating.

[Nickfromwales]

6 hours ago, Sparrowhawk said:

Sounds like this PH architect has designed to the letter of the certification and not to the spirit. Unless the clients have imposed limitations that make it impossible to design out the overheating.

In a nutshell, yes. Way OTT approach tbh.

Just tricky when I’m trying to work with a client and act in their best interests and also not throw someone under the bus (when they’re genuinely doing what they think is the best job they can…..). 
 

Yay. 🥳 

[MikeSharp01]

On 28/03/2024 at 23:27, Cooeyswell said:

0.15U windows

Wow - How is that achieved? I thought PH windows were 0.8 or better - ours are 0.78. Not sure how you could construct a .15 window you can see through.

[SteamyTea]

2 hours ago, MikeSharp01 said:

Not sure how you could construct a .15 window you can see through.

Vacuum in the gap maybe.

[JohnMo]

3 minutes ago, SteamyTea said:

Vacuum in the gap maybe.

Typo maybe?

[Nickfromwales]

2 minutes ago, JohnMo said:

Typo maybe?

Defo.
 

Norrsken’s best offering doesn’t go much lower than 0.7. 
 

Let’s wait for @Cooeyswell to clarify.

[Cooeyswell]

On 30/03/2024 at 08:54, Nickfromwales said:

Defo.
 

Norrsken’s best offering doesn’t go much lower than 0.7. 
 

Let’s wait for @Cooeyswell to clarify.

Sorry folks that number was pulled from memory - and was clearly wildly incorrect.

The average window U-value is 0.9 (Rational Auraplus, Triple glazed, magic coatings etc.)

The house is South facing, Coastal and Northern. Overheating has not been an issue while we have lived here.

Salt deposits on the windows provide all the shading we need 🙂 Not sure how PHPP handles this.

[Kelvin]

On 30/03/2024 at 06:33, MikeSharp01 said:

Wow - How is that achieved? I thought PH windows were 0.8 or better - ours are 0.78. Not sure how you could construct a .15 window you can see through.

Ours average 0.78 too.