Heat Pump Etc

[wcavanagh]

So, currently I have an oil combi heating my 4 bed cottage. We are looking at adding 2 more rooms, and 2 bathrooms, so need to change out the boiler.

I have access to 6kw of very low cost electric, via a solar farm and store etc. So I was wondering about an air source heat pump? Any thoughts. How these preform in Scotland. Should I keep oil as a backup?

House is heated via UFH, currently has, main bathroom, shower room, and cloakroom, will be adding 2 more rooms, each with shower room. Detached well insulated cottage

 

[Swwils]

Get a decent heat loss survey and find out.

Don't rule our air to air heat pump even though you have ufh.

 

[ScottishGasMan]

It's definitely worth looking into. Biggest challenge is finding the right installer as its them that make heat pumps either work or not work. But given price of oil to your elec, and the fact you already have UFH which means potential to run a heat pump at very low temps (which means they run very efficient) then definitely get a look at it.

Due to the way they work even if you needed 10kw of heat output, youd basically never put more than 5kw of electricity into it, and thats on a terrible system, on something set up well that could be 3kw of electricity to get 10kw of heat out.

 

[wcavanagh]

Very interesting, thank you, i will keep looking into HP then

 

[wcavanagh]

Tell me, something like this https://www.screwfix.com/p/samsung-hxsm-g6-041-12kw-air-source-heat-pump-kit-300ltr/756pg

Says 12Kw so is the total system power, or is it 12Kw draw from the mains, e.g. 35 odd amps ?

 

[Swwils]

Most heat pumps will require a 20A or 32A connection and also have their own specific regulations because of their installation location and the nature of the load they introduce, so you may need further electrical work to enable it.

You absolutely want the system installed and designed by a specialist who actually knows what they are doing. Have a look at heatgeek for a supplier near you.

 

[ScottishGasMan]

Dunno much about Samsungs. They will need backup/immersion heaters being an R32 model which will probably bump up the quoted energy draw.

You judge them off their SCOP figure (seasonal performance) as the efficiency and power input is constantly changing depending on the outside temperature and flow temp they are required to produce (which is also constantly changing as you only need the higher flow temp for winter)

The likes of the Vaillant aroTHERM Plus 10Kw. Gives a SCOP of 5 for a system designed for 35 degree flow temp. this means on average over the year, for heating, you put 1kw electricity in and get 5kw of heat out.

Typically SCOP you want at least 3. 4 is a pretty good system, 5 is a very well designed system. But there are a lot of vairables that affect this which is where a good Heat pump engineer is required to maximise the efficieny of the system

 

[wcavanagh]

Ahhh I see, thank you, now I understand. So I run my UFH at 38C so that would work well, how do you go about DHW?

 

[bernardgreen]

on something set up well that could be 3kw of electricity to get 10kw of heat out.

That heat output is only possible if the evaporator ( the outdoor unit ) can harvest 7 kW of heat from the air. Harvesting that much heat may not be possible when the temperature of the ambient air is close to freezing point

 

[ScottishGasMan]

Ahhh I see, thank you, now I understand. So I run my UFH at 38C so that would work well, how do you go about DHW?

Yes very well. What I would do is remove any UFH mixing valves from the manifolds, I assume the oil boiler runs higher temp than 38⁰ and then the UFH mixes it down like most systems would.

For a great HP system, you do away with those mixing valves and just tell the heat pump to run at 38⁰c in cold weather (it will flow cooler than 38⁰c in spring/autumn as you won't need as much heat then again increasing the efficiency if the unit)

Hot water depends on the type and make of heat pump, im only very familiar with the vaillant units. The one I mentioned previously can reach 75⁰c flow temps so heats hot water cylinder on its own with no fuss.

Older types of units heat hot water up to say 40-50⁰c then use immersion to top heat up further.

Although if you have space you install a bigger cylinder and only heat it to about 50⁰c anyway most of the time (efficiency) no point heating something up hotter only to blend it back down.

 

[ScottishGasMan]

That heat output is only possible if the evaporator ( the outdoor unit ) can harvest 7 kW of heat from the air. Harvesting that much heat may not be possible when the temperature of the ambient air is close to freezing point

You size the heat pump to a set design outdoor temperature, then it gives you whatever you sized it to at that temperature outside. UK units generally work to about -20⁰c outside. And where I live you size them to cover the full heat load to about -5⁰c outside.

In this case if temperature drops below -5⁰c then it won't be able to maintain 20/21⁰c in the house. That's when backup heaters kick in. Or you stick on a fan heater.

They cover 100% of the load for about 99% of the year.

 

[MeldrewsMate]

...Although if you have space you install a bigger cylinder and only heat it to about 50⁰c anyway most of the time (efficiency) no point heating something up hotter only to blend it back down.

Unless you want to avoid breeding legionella, by which I mean you must heat the entire contents of the cylinder to 60C about once per week.

 

[ScottishGasMan]

Unless you want to avoid breeding legionella, by which I mean you must heat the entire contents of the cylinder to 60C about once per week.

As much as its incredibly unlikely to get legionella off of a mains fed mains pressure cylinder, they have legionella programs built into their controllers.

Although legionella will die in 2hrs at 50⁰c any responsible installer would ensure that a once weekly legionella schedule would be set