Which heating and hot water solution(s) in 2024?

[ChrisInKent]

The rules have changed on ASHP grants recently, if you’re a self-builder have a look. https://www.gov.uk/apply-boiler-upgrade-scheme/check-if-youre-eligible

‘If you own a self build property

Your self build property is eligible if:

• you or the original owner built it yourself or you paid a builder to build it
• it’s never been owned by a business or organisation

You’ll need to show your installer proof that your property is a self build, for example, a copy of the title deeds.’

 

[Nickfromwales]

5 hours ago, G and J said:

I guess I’m thinking of our own situation but if there is an ASHP why not use that to efficiently use Solar PV to do free UFH and/or DHW? (Or isn’t it that simple?)

It's very simple.

In the winter when you turn the heating on, for the 3-4 months of the year that you will be heavily reliant on space heating (in the majority of homes) you'll be at <25% or less PV production, so if you have a 4kWp array you'll not be getting even a reliable 1kW of PV production (when it's one of the sunnier days in the heating season ). That <1kW will be sucked up by the house, so there's "goodbye" to any dreams of diverting excess ANYWHERE as you won't have any.

If, for eg, you have space & budget for an 11-12kWp array (maxed out on 3ph, for eg) and it's all South facing, then maybe you'd still get DHW from excess. But even with that size array, during the heating season, you'll be very lucky to get a reliable 2-3kW return from the array. Costs of PV then go beyond the costs of just feeding cheap, grid electricity into the ASHP in the 1st place, for dumping steady low grade heat into a big thick insulated raft slab as a 'storage heater'.

 

Get the calculator out, remove the rose-tinted goggles, and the evidence will support itself.

[G and J]

11 hours ago, Nickfromwales said:

It's very simple.

In the winter when you turn the heating on, for the 3-4 months of the year that you will be heavily reliant on space heating (in the majority of homes) you'll be at <25% or less PV production, so if you have a 4kWp array you'll not be getting even a reliable 1kW of PV production (when it's one of the sunnier days in the heating season ). That <1kW will be sucked up by the house, so there's "goodbye" to any dreams of diverting excess ANYWHERE as you won't have any.

If, for eg, you have space & budget for an 11-12kWp array (maxed out on 3ph, for eg) and it's all South facing, then maybe you'd still get DHW from excess. But even with that size array, during the heating season, you'll be very lucky to get a reliable 2-3kW return from the array. Costs of PV then go beyond the costs of just feeding cheap, grid electricity into the ASHP in the 1st place, for dumping steady low grade heat into a big thick insulated raft slab as a 'storage heater'.

 

Get the calculator out, remove the rose-tinted goggles, and the evidence will support itself.

Interesting.  I suspect that my thinking is unconsciously based on my current house which needs heating a lot more than 4 months of the year.  Ergo some heating is needed when there is possibly spare solar pv output.   We’re not going passivehaus but we are going as airtight as poss, slightly better than building regs wall insulation and not that much glazing, and a decent MVHR.  So in those circumstances should I be thinking my ASHP will be hot water only 8 moths of the year?

[JohnMo]

44 minutes ago, G and J said:

Interesting.  I suspect that my thinking is unconsciously based on my current house which needs heating a lot more than 4 months of the year.  Ergo some heating is needed when there is possibly spare solar pv output.   We’re not going passivehaus but we are going as airtight as poss, slightly better than building regs wall insulation and not that much glazing, and a decent MVHR.  So in those circumstances should I be thinking my ASHP will be hot water only 8 moths of the year?

Just think you are not really understanding what PV does or doesn't do. This time yesterday I was generating 3kW, today because its cloudy 600W. Relying on PV to do anything predicable is rose tinted glasses and headphones on mode. It does what it does when the weather allows.  Your heating is generally running max load when the sun isn't out, when the sun is out you get solar gain in the house etc.

 

During the winter this year lots of rain and many days with next to no generating from PV. But boxing day was sunny and we did the whole lunch powered by solar. Averaged over a whole it will generate xkW, next week is anyone's guess

[G and J]

10 minutes ago, JohnMo said:

Just think you are not really understanding what PV does or doesn't do. This time yesterday I was generating 3kW, today because its cloudy 600W. Relying on PV to do anything predicable is rose tinted glasses and headphones on mode. It does what it does when the weather allows.  Your heating is generally running max load when the sun isn't out, when the sun is out you get solar gain in the house etc.

 

During the winter this year lots of rain and many days with next to no generating from PV. But boxing day was sunny and we did the whole lunch powered by solar. Averaged over a whole it will generate xkW, next week is anyone's guess

I’ve explained my question poorly, apologies.  Let me try again forgetting anything solar. 
 

How many months of the year am I going to run my UFH?  
 

 

[JohnMo]

1 minute ago, G and J said:

 

How many months of the year am I going to run my UFH

How long is a piece of string, maybe late September or early October to start or end of April, depends on the weather really and how your house is affected by it. 

[Jane W]

20 hours ago, Nickfromwales said:

Diversion of excess solar?
 

So, if you need heating, it’ll not be a sunny day, ergo most if not all of anything you produce from an average sized array will be sucked up by the house base loads and possibly a bit of DHW    

Solar > space heating = no dice. 

Not from solar, I was thinking from the heat source so from the boiler or ashp

[Iceverge]

On 03/05/2024 at 13:35, Jane W said:

Thank you, that setup is of interest. Have you any thoughts on a diversion to heat the supply air in the mvhr, similar to Denby Dale. I know it was used to reduce short cycling there but presumably it could also work with an ashp. I wonder how effective that would be?

 

MVHR only heats a small volume of air. There is practical temperature limits. If for no other reason than the risk of melting elements of the ducting etc. Passivhaus set this at 50⁰ as mentioned above .

 

This limits the energy that can be transferred to about 10W/m². 

 

As your house won't meet this figure you will need some other heating system like rads or UFH. These are all capable of delivering well above the required power for your house on their own so adding MVHR air warming when it's not required would be money spent for nothing. 

 

 

 

 

 

Edited May 5 by Iceverge

[SteamyTea]

2 hours ago, Iceverge said:

This limits the energy that can be transferred to about 10W/m². 

Double the diameter of the ducts and you quadruple the mass flow rate, so could up that 10 40 W.m^-2 for the same flowrate.

 

I assume we use relatively small diameter pipework for ease of installation.

[JohnMo]

2 minutes ago, SteamyTea said:

Double the diameter of the ducts and you quadruple the mass flow rate, so could up that 10 40 W.m^-2 for the same flowrate.

But why, bigger MVHR unit, 4x the heat loss by ventilation and maybe more noise and drafts. Just keep it simple. Floor or radiators single zone - done

[SteamyTea]

19 minutes ago, JohnMo said:

But why

Because it can be done.

But yes, probably not something I would do in reality.

[Iceverge]

13 minutes ago, SteamyTea said:

Because it can be done.

But yes, probably not something I would do in reality.

 

Regularly done in the bits of North America that are covered in snow for 6 months of the year.

 

Think it is called forced air heating or something like that. 

 

 

[SteamyTea]

12 hours ago, Iceverge said:

 

Regularly done in the bits of North America that are covered in snow for 6 months of the year.

 

Think it is called forced air heating or something like that. 

 

 

Yes.

And oddly, US thermal building codes became quite strict after the 1973 oil embargoes.

Partly why the USA is the largest (by tonnage) oil producer in the world, they don't want to get caught with their pants down again.

 

We had forced air heating, and A/C in our place in Pennsylvania, a big oil furnace and then an even bigger heat pump.

Was a strange climate though, had 6 days to get spring and autumn out the way, then it was either -30⁰C or 30⁰C.

Humidity was between 25% or 100%.

Why we stayed in all the time and watched TV.

[severnside]

We used old warm air ducting attached to A2A ASHP. It works well and very quiet. We also have some wall mounted split units in new part of house, they are more efficient but slightly noisier than ducted one. This is in England for reference. 

[SteamyTea]

7 hours ago, severnside said:

We used old warm air ducting attached to A2A ASHP

Would be easy to fit MVHR as well.

 

When I was a lad, the house across the road from us had forced air heating, I do seem to remember that their daughter told us that she could hear conversations easily in her bedroom.

I don't remember it being a problem when I was in PA.