Heat pump / inverter DIY

richardc1983

YOu may start off initially with a room that is 20C but eventually the room temp may drop to -20!

Ammount of heat drops in the air as the air temp falls. They are called outdoor units for a reason!

Cardew

ABN wrote: »

As I see it the efficiency gain by these systems is directly related to the air temperature, the higher the ambient temp the more efficiency gain you get. Now assuming you have the space for a small sound proof(ish) boiler room within the house can units that are normally mounted outside be moved inside and hence use the higher internal air temp of the house. This would mean that eventually they would be working at 20C+ and be super efficient. Ideally the rest of the house would be heated via ductwork rather than separate small units placed around the house.

As said probably a stupid suggestion but would be interested as to why.

These units are, in effect, a refrigerator working in reverse.

The back of your normal fridge gets warm as they extract heat from inside the fridge - well ASHPs use that principle(i.e. they use that heat) to warm your house.

The boxes are mounted outside because they are trying to cool down the air surrounding 1 Railway Cuttings East Cheam(if that is your address).

They get very cold and are required to have a defrost cycle.

Your idea would be wonderful - akin to perpetual motion - but sadly it won't work.

thechippy

Johnhowell wrote: »

G.

Many thanks for this. If you require any other information please do not hesitate in asking - I shall monitor throughout the day.

John

Hi John,

I've carried out the calcs.
You have to size a conservatory system according to cooling demand, especially a south facing one, as the solar gain in the summer will be high.

Your cooling demand would be approx 7kw under these circumstances. You only need 4kw of heating, but should you size to this, the system will only give about 3kw of cooling, which is a waste of time. These systems work more efficiently in heating mode! Use a 7kw inverter (nominal cooling) and it will produce more than enough heat on the coldest day.

Does this make sense?

G.

richardc1983

Yes and because they are inverters they will ramp down even if oversized for the room so will provide less capacity if needed. Its always best to oversize based on this.

paceinternet

Just to expand on the ABN question about a boiler room, as it has been explained that air flow is needed through the unit which exits much cooler than the inlet air, so an enclosed room would not function correctly.
However, in principle, if you created an air inlet and outlet to the room with some other heat source in the room (solid fuel / wood burning stove), then you would gain some advantage.

This is how heat recovery units work, and it may well be a future design consideration for buildings to extract the potentially wasted heat from the roof space or other heat generating equipment.

thechippy

paceinternet wrote: »

Just to expand on the ABN question about a boiler room, as it has been explained that air flow is needed through the unit which exits much cooler than the inlet air, so an enclosed room would not function correctly.
However, in principle, if you created an air inlet and outlet to the room with some other heat source in the room (solid fuel / wood burning stove), then you would gain some advantage.

This is how heat recovery units work, and it may well be a future design consideration for buildings to extract the potentially wasted heat from the roof space or other heat generating equipment.

...It's not new, been going on for years. Waitrose were doing it 15 years ago.
I was working in thier Chichester branch and the heat from the condensers on the refrigeration equipment in the plantroom was ducted off and used to suppliment the heating to the shop floor.
Many vrf systems are capable of this now and widely used in office blocks etc.

richardc1983

The chippy, you beat me to it i was going to mention VRF systems!!!

Johnhowell

thechippy wrote: »

Hi John,

I've carried out the calcs.
You have to size a conservatory system according to cooling demand, especially a south facing one, as the solar gain in the summer will be high.

Your cooling demand would be approx 7kw under these circumstances. You only need 4kw of heating, but should you size to this, the system will only give about 3kw of cooling, which is a waste of time. These systems work more efficiently in heating mode! Use a 7kw inverter (nominal cooling) and it will produce more than enough heat on the coldest day.

Does this make sense?

G.

Thank you thechippy for doing the calculation. So a 24000BTU unit it is!!!
Thanks to Richardc for the confirmation.

Regards,
John

richardc1983

Johnhowell u can add to our reputation by pressing the thanks button.

Johnhowell

richardc1983 wrote: »

Johnhowell u can add to our reputation by pressing the thanks button.

Done.
John