How much am I looking at to get an air/air heat pump/air con installed

[chrisgeller]

1990's bungalow and well insulated.

 

Only looking for something to be able to heat (and rarely, cool) the living and kitchen space which is about 400sq ft. Want to avoid changing radiators, underfloor heating etc, and will still have other options for heating.

 

Looking for a cheap and cheerful way to avoid burning fossil fuels. What kind of COP should I be expecting in normal use?

[PeterW]

You’ll be burning fossil fuels but at the power station unless you’re on a renewables only tariff but even then you will influence the base load anyway. 
 

A cheap A2A will be sub £1k and can nearly be self installed if you get the pre-gassed ones. Otherwise you need an FGas ticket and vacuum pump etc to install it. 
 

Standard A2A at 7°C will run about CoP 3 so isn’t as efficient as gas based on price alone. 
 

First consideration for me would be double the size of the rads.  Is this a generally cold room ..?

[chrisgeller]

Thanks Peter! Yup, I'm on a renewable tarriff, but take your point about baseload - it's hard to be truly zero-carbon!

 

I guess taking your COP, with the grid  operating at 160gCO2/kWh right now, so with a COP of 3 that's 160g CO2 for 3kWh of effective heating.

 

Natural gas for heating is around 185gCO2/kWh, so that's 185*3= 555g CO2 for the same amount of heating. 

 

No, it's a generally pretty warm area, the existing gas heating along with the insulation doesn't really struggle. Not too worried about it being very slightly pricier in use.

 

I guess the way I'm thinking about it is that if it only costs about a grand, has a decent chance of actually providing the required heating, and doesn't cost too much more in use, I might as well go for it.

 

I'm looking at models like this - are there any reliable ways to see if that will actually meet my needs?

 

Thanks again

 

https://www.amazon.co.uk/12000-Quick-Connector-Conditioner-Conditioning/dp/B07CRR35NW/ref=zg_bs_306928031_36?_encoding=UTF8&psc=1&refRID=C5GD23GGX2ZN546BSZ9X

[SteamyTea]

I would not get hung up on the electrical grin carbon intensity, we have little influence on that, it is what it is at any given time (and some of the calculations are a bit dodgy).

 

Have you calculated your current heat and DHW loads.  This is the first thing to do.

[PeterW]

Consider one of the all in one units that only need the wall drilling for a pair of vents if it’s only one room. 

[chrisgeller]

32 minutes ago, SteamyTea said:

I would not get hung up on the electrical grin carbon intensity, we have little influence on that, it is what it is at any given time (and some of the calculations are a bit dodgy).

 

Have you calculated your current heat and DHW loads.  This is the first thing to do.

Thanks SteamyTea - not interested in DHW for now, really only looking at heating with air/air. What would you say was the best way to measure the heat load - just looking at the gas used?

[SteamyTea]

17 minutes ago, chrisgeller said:

just looking at the gas used?

Yes.

You can take a few kWh/day off for DHW.

Then proportional the rest by month to give you an idea of maximum heat loads.

[chrisgeller]

6 minutes ago, SteamyTea said:

Yes.

You can take a few kWh/day off for DHW.

Then proportional the rest by month to give you an idea of maximum heat loads.

Got you, thanks. Is there any reliable way to get to the solution? I can work out the kWh needs, the kW needs on a cold day, and use the COP of a candidate heat pump to work out what kW/BTU I'll need - but that all seems a bit too simple! For example, should I leave a bit of a buffer? Is there a recommended way to calculate that?

[SteamyTea]

55 minutes ago, chrisgeller said:

but that all seems a bit too simple

It is, and I never understand why people think it is complicated.

56 minutes ago, chrisgeller said:

should I leave a bit of a buffer

With a heat pump there should be an air and power chart somewhere in the documentation. Use that to calculate the worse case. General consensus is that air to water heat pumps need to be oversized by 20% to 30%.

Not quite so important with an A2A as you can easily supplement with s fan heater.

[DamonHD]

2 hours ago, chrisgeller said:

Got you, thanks. Is there any reliable way to get to the solution? I can work out the kWh needs, the kW needs on a cold day, and use the COP of a candidate heat pump to work out what kW/BTU I'll need - but that all seems a bit too simple! For example, should I leave a bit of a buffer? Is there a recommended way to calculate that?

You can take daily gas readings and convert to kWh, and gather daily heating degree days (eg see degreedays.net), for at least three weeks, load into your favourite spreadsheet and the SLOPE() is your heating efficiency in kWh/HDD, and the INTERCEPT() (at 0HDD) is your non-space-heat baseload.

 

From the heating efficienct and the greatest daily HDD you see at your location you can estimate peak heat demand.

 

Simples.

 

Rgds

 

Damon

[TonyT]

Should be reasonably cost effective as cabling and pipework is easy in a bungalow if it’s going up and then back down.

[chrisgeller]

2 hours ago, DamonHD said:

You can take daily gas readings and convert to kWh, and gather daily heating degree days (eg see degreedays.net), for at least three weeks, load into your favourite spreadsheet and the SLOPE() is your heating efficiency in kWh/HDD, and the INTERCEPT() (at 0HDD) is your non-space-heat baseload.

 

From the heating efficienct and the greatest daily HDD you see at your location you can estimate peak heat demand.

 

Simples.

 

Rgds

 

Damon

Fantastic! Cheers, this exactly the kind of detail I was looking for. Looks like a great resource.

 

Concept understood, I'll have a play with it tomorrow.