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Ducting an air source heat pump for the purpose of potentially fitting it the cellar

Gild · 2024-09-14T08:03:45Z

Hello. TL;DR: Is it possible to put an air source heat pump in a cellar and placing the exhaust into a duct to push the cold air through a hole in the wall as large as the ran's apartue? Longer version: We own a summer house in Shetland. It's a non-listed property that has the basement(s) and half of the ground floor built around the 1800s (rubble filled stone wall) and the rest of the property built in the 70s with double block walls with no insulation between the leafs. We are slowly getting the house more and more insulated including a recent replacement of all old windows with modern triple glazed argon filled windows and a major hunt for all draft points and placing kingspan every time we touch a wall that has bad insulation. I would also like to replace the heating system that consists of storage heaters plus underfloor electric heating The storage heaters are practically useless during the summer as during sunny days we get lots of heat from the velux windows and have to vent the stored heat (so we normally just keep them off but then on a cold day we need to turn on electric radiators) and the electric underfloor heating is extremely inefficient and expensive to run. I would really like to install a heat pump with underfloor heating throughout the house but we have nowhere to put the pump! We have no grounds and putting it on the wall is a big no no as we are in a conservation area. What I had hoped to do. Is put it in one of our basements (we have 2). It has a door facing the outside and if we drill holes in the door or replace it with a grilled net - it would provide a way to get fresh air into the basement but the problem is getting it out. I thought about drilling a large hole. Through one of the basement's walls and duct the heat pump exhaust through it. I am simply wondering if the heat pump fan can cope with the static pressure of a ~1 meter duct and if I am missing anything else. I understand that 8kw units have a single fan so that would be our limit I guess (there is no way to bore 2 holes. Happy to hear your thoughts. Thanks.

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Air Source Heat Pumps (ASHPs)

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Mars

(@editor)

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14/09/2024 9:34 pm

@gild yeah, that’s a tricky one. I just don’t think the cellar is going to work. I’ve had hypothetical conversations with installers about air source heat pumps in garages, sheds, outbuildings, etc. and it always comes back to movement and replacement of air. I’ll put this question to some knowledgable installers this week. I’m recording my next episode of Homeowners’ Q&A and this could be a great question.

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Anonymous 5011

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14/09/2024 9:47 pm

No idea how big a heat pump you need, but this would easy to do, or even cascade 2x.

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This unique system is a much simpler and cheaper way (around 70%) of installing heat-pumps into apartments against using HIUs central plant rooms and ground source heat-pumps.

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Gild

(@gild)

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Topic starter 14/09/2024 10:08 pm

@editor Thanks! Fwiw I can open enough intake area for the basement that would be roughly twice the fan's apartue area. Maybe even more.

The alternative would be to install an oil boiler which would be a sad thing to do in 2024...

@johnmo Thanks! That's interesting as it's actually small enough that I can put it in different sides of the house (maybe in the other basement too) I think I'll need 3.

Are.these inverter units? I'll start reading more. Edit: I see a buffer in the installation doc so probably no inverter:/

Cheers.

This post was modified 11 months ago 2 times by Gild

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Anonymous 5011

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14/09/2024 10:22 pm

Posted by: @gild

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Are.these inverter units?

Would doubt it. But my 6kW inverter ASHP is running at around 4 to 5kW are the moment no less. So cascade them you should be able to 3x 3kW when really cold and 3 kW when just cold enough to need heat. 30 min on off cycle your down to 1.5kW etc.

From reading the manual (many months ago) I recall the ability to drive an external heat source, this could drive a second unit easily enough then a third I would think.

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AllyFish

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16/09/2024 8:48 am

The problem with ducting or enclosing a ASHP is adding external static pressure (ESP) to the fan. The fan impeller is designed to move large volumes of air with no ESP other than the unit evaporator coil and inlet and outlet grilles. As soon as you add anything else into the airflow; a grille, louvre, a duct, a deflector or hit'n'miss fence, etc., you add ESP to the fan & reduce the volume flow through the unit. That will impair the capacity and performance of the ASHP, with risk of the ASHP starting to recycle air that it has already processed, or the fan going into a stall, which is where the airflow through the fan impeller collapses and drastically reduces.

You could include a second in-duct fan in series with and interlocked and controlled by the in-built ASHP fan, and this is sometimes done with split A2A systems or ducted cooling systems in basements or cellars, but it needs specialist design, and the second fan generates noise and consumes additional power. System efficiency is always lost.

I've read acoustic reports where an acoustic engineer's suggestion is to acoustically enclose an air-cooled machine or air source heat pump unit. Well, it fixes the noise problem, but so reduces the capacity of the unit that you might as well switch it off, which is a cheaper and simpler solution!

This post was modified 11 months ago by AllyFish

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Gild

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Topic starter 17/09/2024 6:04 pm

Thanks @allyfish . Yes, I mentioned static pressure as the main issue here. That's why I specifically wondered about the exaust as this will be the real ducted part.

The inflow will be nearly resistant free I think, as I can create a large opening for the cellar. (depending on how I'll do it, but can be twice or 4 times the surface area of the fan) so it should be pretty free for the air supply.

I am not worried about acoustics there to be honest, there is a thick concrete ceiling between where I want to place it to the house.

Thanks again for taking the time for your detailed answer!

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