Choosing DHW system for a new build passive house (with PV and direct electric space heating)

[Nickfromwales]

45 minutes ago, Iceverge said:

 

Had a quick scan of https://www.theunderfloorheatingstore.com/electric-underfloor-heating/inscreed-heating. Thought 3* 2600w kits would do 250m²?

 

TBH I'm almost convinced to get the consaw out to our 150mm slab and put in pipes myself. 

So, is this a retro-fit? It’s a bit tricky to keep up with everything / everyone here tbh  so remind me please. 

[Iceverge]

29 minutes ago, Nickfromwales said:

So, is this a retro-fit? It’s a bit tricky to keep up with everything / everyone here tbh  so remind me please. 

 

No new build passive house 2021 finish. No CH installed. Just a plug in heater or two. 

 

I think my wife will agree to it only if she can bury me under the new slab.

 

150mm 35N concrete slab with a batch of A393 for good measure so I don't think I'll be undergoing that idiocy. Just an high COP A2A at some stage. 

Edited March 10, 2023 by Iceverge

[Nickfromwales]

3 minutes ago, Iceverge said:

No new build passive house 2021 finish. No CH installed. Just a plug in heater or two. 

 

I think my wife will agree to it only if she can bury me under the new slab.

Sacrifices have to be made.

I'll have a chat with her later today. Have you been keeping up to date with your over 50's plan?

 

 

 

So, without poking the bear with a sharp stick, are you one of the PH believers who is now reconsidering their "faith"?

[Nickfromwales]

A few strategic, and very well positioned, IR panels are now sounding an option tbh.  

[Iceverge]

1 hour ago, Nickfromwales said:

Sacrifices have to be made.

I'll have a chat with her later today. Have you been keeping up to date with your over 50's plan? 

 

She'll have to wait a few years, I see her regularly crossing off the days mind you. .....

 

1 hour ago, Nickfromwales said:

So, without poking the bear with a sharp stick, are you one of the PH believers who is now reconsidering their "faith

 

Yes and No. 

 

 

YES:

I'm completely on board with the airtightness, 3g, MVHR, attention to thermal bridging. The house "coasts" so well through outside temperature variations. The bitter and extra windy weather last night was imperceptible inside.  We are living more comfortably than any other house I've lived in and despite being direct electric is still much cheaper than most ASHP new builds I know to heat.  In terms of KISS our CH works and a plug in rad or two doesn't get much simpler. 

 

NO:

The 10w/m² peak heating load target is based on space heating of the house with supply air from the MVHR and hence is a bit arbitrary. Similarly the 15kWh/m²/annum heating demand. Doing PH can be quite an evangelical process as you have to do so much conversion of the doubters. In so it's easy to become swallowed by the doctrine. In reality 16kWh/m2/annum or 

14kWh is neither here nor there and probably far outweighed by how much your kids let the door open. 

 

I would have gone for 300mm EPS floor insulation rather than 200mm and 300mm rather than 250mm EPS beads in the walls if I was to go again. The cost is marginal and would have taken us to about 8w/m² and 12kWh/m². No reason to stop at PH targets either. 

 

PH assumes 20⁰ is fine for every room. It is, but really 18/19⁰ in the bedrooms and 24/25⁰ in the bathrooms would be better. 

 

PH can put the kibosh many lovely design elements like roof lights at the cost of some minimal active heating/cooling. 

 

When we were building however almost everyone who didn't sing from the PH hymnsheet with regard to targets, airtight, heating load/demand etc was a bluffer and would have I'm sure landed us with a house that fell far short of design levels. 

 

TLDR.

 

PH and PHPP absolutely work, use them but don't treat them as targets/limits and don't let the methodology limit you from making an excellent house an exceptional house. 

[Nickfromwales]

A Beattie PH?

[Iceverge]

No, cavity wall with strip foundations. 

[Gone West]

6 hours ago, Nickfromwales said:

PH lifestyle would probably better suit someone retired who could accept a 24/7/365 functionality. 

Yes it suited us perfectly but everyone is different and when you throw kids into the equation it muddies the waters no end. We wanted a straightforward simple and economical to run house, which is what we built. No complex controls. When we put it on the market the people who bought it wanted the same as us and were willing to pay the extra to have it. PH wouldn't suit everyone, especially those who want windows open all year round and a WBS roaring away. When we built our PH we were members of the AECB and had a lot of contact with architects and PH designers. I was very surprised at some of the basic mistakes they made and yet they were supposedly experts.

[Iceverge]

  

On 23/02/2023 at 10:44, Nickfromwales said:

FYI, most ASHP's will have a stated service life of 7 or ( a few ) more years

 

Stolen quote from a different thread. 

 

Doing the sums:

 

Based on an installed cost of €6000 for an ASHP and UFH and €2000 for a WILLIS and UFH

Our space heating of 2500kWh/annum (COP of 4 for the ASHP) 

DHW of 3200kWh ( COP of 2.5 for the ASHP) 

Day rate of 48c/kWH and Night rate of 14c/kWh then the total 7 year cost of €7831 for the ASHP and €7,666 for the Willis. Assuming zero maintenance for both. 

 

With double the space heating (5000kWh) the sums are €2k in the ASHP favour. 

 

Except for the cooling I don't think there's a case for ASHP in low heat demand houses.  Maybe the transition from ASHP to Willis is a good marker for how passive is passive enough. 

 

Even with our current system of direct electric rads the 7 year cost is €8603. Swap out for a good A2A @ €2000 installed cost and the cost drops to €6,374. 

 

 

On 10/03/2023 at 10:04, Nickfromwales said:

A few strategic, and very well positioned, IR panels are now sounding an option tbh.  

 

 

Any recommendations, for what brands? We have a fused spur in the bathroom + ensuite crying out for exploitation.  

 

 

 

Edited March 13, 2023 by Iceverge

[joth]

On 10/03/2023 at 08:27, Gone West said:

 

When I designed my house back in 2009 I was using the 2007 version of PHPP which IIRC, (subject to my squishy brain), didn't have the room by room analysis option. I can see that there could be advantages in carrying out a room by room analysis in a very large, poorly designed house, but it wouldn't have been an advantage to me. It's really best to follow the PH design principles as closely as possible.

The 2018 version of PHPP also didn't have room by room analysis. It has "critical room" analysis for one room, for heating only. But PH is a whole-house philosophy and doesn't really think about rooms as individual units, especially not for cooling needs.

So +1 @Nickfromwales about not getting lost while drinking passiv  Kool-Aid 

 

[markocosic]

ASHP to do hot water and a bit of space heat?

 

Does that not move the payback numbers?

 

If you have UVC anyway getting one with a big coil is not much of a delta.

 

Space heat is pipe the thing into the UFH with a 3-port valve to switch between it and space heat.

 

+£3.5k vs Willis not €6k?

 

https://midsummerwholesale.co.uk/buy/vaillant-heat-pumps/vaillant-arotherm-plus-5kw