Mixergy's new heat pump hot water cylinder (iHP)

markin

orbit500 said:

And where does this extract the heat from? The house, which you’ve paid 10p/kWh to heat?

It would be pointless having it in the heated part of the house, A Garage with added ventilation or cellar would be the most likely best location, A drafty loft would be great apart from the potential noise problems, With 300mm of insulation or more the heat pulled from the house would be very little

Grandad2b

Reed_Richards said:

Grandad2b said:

I don't know your house but I would guess the volume of air in the loft is smaller than the volume of the rest of the house. How long will it take to use the energy being 'stored' in the loft?

It's a pitched roof that I can stand up in so the volume of the loft must be close to half the volume of the rest of the house. 

I looked it up and air has a heat capacity of 700 J per kg per K and water has a heat capacity of 4184 J per kg per K.  So heating a kg of water by 1 C would reduce the temperature of a kg of air by 6 C.  A kg of air occupies about 0.82 m3 and a kg of water occupies 1 litre.  So if you have a 250 l hot water tank and want to raise its temperature by 1 C you would need to reduce the temperature of 1225 m3 of air by 6 C.  If my roof is 2.5 m high at the apex then its average height is 1.25 m so I need a floor area of 980 m2 to have 1225 m3 of air in the loft.  I live in a bungalow and actually have about 200 m3 of floor area. 

So either I have done the calculation wrong or I've talked myself out of the idea of extracting heat from the loft on the basis that there isn't nearly enough.  I think I have also reasoned myself out of using an exhaust air heat pump.  Have I made a mistake?       

Thanks for taking the time to do the calculation - I don't think you've made a mistake.

anon_ymous

Is this comparable to an Arastor? Would this be the better product to go for too? 

Screwdriva

Yes but far superior based on initial feedback. The Vaillant AroStore was a first generation product and was really slow at heating up water. No such problems with the iHP.

QrizB

markin said:

orbit500 said:

And where does this extract the heat from? The house, which you’ve paid 10p/kWh to heat?

It would be pointless having it in the heated part of the house

Other manufacturers of similar devices (there are several) suggest installation inside the house, with ducts and dampers arranged to allow air to be drawn from and returned to either indoors or outdoors depending on season.

In the winter, you draw from outdoors and return the cooled air outdoors.

In the summer, you draw from the house and return the cooled air to the house.

Screwdriva

More data here!

https://mixergy.co.uk/wp-content/uploads/2023/09/IHP.pdf

Reed_Richards

Go on @Screwdriva, you know you want to get one.

markin

Do we know the price of it yet?