Ducting an air source heat pump for the purpose of potentially fitting it the cellar - Air Source Heat Pumps (ASHPs)

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

Gild — Tue, 17 Sep 2024 17:04:46 +0000

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!

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

AllyFish — Mon, 16 Sep 2024 07:48:42 +0000

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!

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

Anonymous 5011 — Sat, 14 Sep 2024 21:22:39 +0000

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.

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

Gild — Sat, 14 Sep 2024 21:08:44 +0000

@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.

RE: Ducting an air source heat pump

Anonymous 5011 — Sat, 14 Sep 2024 20:47:38 +0000

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

https://trianco.co.uk/activair-indoor-9111-9111

RE: Ducting an air source heat pump

Mars — Sat, 14 Sep 2024 20:34:00 +0000

@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.

RE: Ducting an air source heat pump

Gild — Sat, 14 Sep 2024 20:09:13 +0000

Thank you all.
I am not trying to make things complicated. I have no place to put a heat pump as our property doesn't have any land beyond the house itself and the only wall I can in theory use - is facing the street in a conservation area and this will never get planning permission (not to mention that it will be detrimental to the street so I don't even want to try).

RE: Ducting an air source heat pump

Mars — Sat, 14 Sep 2024 13:34:14 +0000

@gild, there are alternatives like water source and ground source heat pumps, as Derek suggested. However, these systems can be incredibly expensive to install, and in many cases, the cost can be prohibitive, even if you’re located near the sea. Water source heat pumps, particularly those drawing from rivers or the sea, are extremely efficient and a fantastic option for those living near reliable water sources.

Is it legal? That’s a good question. Using sea water for a heat pump would likely require permits, as the shoreline in the UK is indeed owned by the Crown Estate, which manages the seabed and foreshore. If you’re considering using sea water as a heat source, you’d need to check with local authorities about permissions and regulations.

As for how they work, sea water source heat pumps are different from ground source heat pumps. Instead of burying pipes in the ground or down a borehole shaft, the heat exchange pipes are submerged in the sea (or other water bodies). There are technical challenges, especially related to the corrosive nature of salt water, which can severely damage the pipes and other components. Because of this, specialised materials, such as corrosion-resistant coatings and marine-grade metals, are used to avoid degradation over time.

That said, as johnmo mentioned, an external ASHP is likely your best solution. Installing one in your cellar, unfortunately, may not yield the best results due to the challenges in airflow and space.

RE: Ducting an air source heat pump

Anonymous 5011 — Sat, 14 Sep 2024 11:58:54 +0000

Why are you making something easy so difficult, put the ashp outside.

It a get a dedicated indoor unit, where you put 2 x 150mm holes through the wall. But you will be limited to 3kW.

RE: Ducting an air source heat pump

Derek M — Sat, 14 Sep 2024 11:21:10 +0000

I'm just providing possible solutions, whether they are legal or feasible is for you to explore.

Water has a specific heat capacity that is approximately 3500 times greater than air, so instead of the 30 to 50 cubic metres per minute of air stated by Mars, for the same thermal energy you would require 8.6 lpm to 14.3 lpm of sea water.

Would it be possible to draw water from the sea into your basement, pass it through a heat exchanger connected to a GSHP, and then send the cooler water back to the sea?