Winter heating in the UK! Air source heat pump?

Hello wonderful folk,

Investigating ways to heat the aquaponic system we are building. We have 12 IBC totes for our fishies (common carp). We'll probably not get time to implement a heating system for this winter so they will have to put up with the cold and hibernate... but for next year, if our system is successful and still running it would be great to have heating in the winter.

One idea I had for keeping our fish warm is implementing an air source heat pump. Has anyone tried using an air source heat pump in a separate closed loop system? The loop would be heavily insulated aside from coils that are submerged in the fish tanks for exchanging the heat. Would these coils be enough to take the edge of things for the fish, or am I missing something and this is a hopeless notion?

I've attached a few pics of our tanks and a sketch of what I'm rambling about...







We would start with a coil in just one tank to start with and then add more if the pump seems to cope okay. The pump in question would probably have a heating capacity of between 5 - 8Kw as we are limited to a pump that sucks under 2Kw of juice.

Many thanks!

Sean

Hi Sean,
Ground source heat pumps work better in winter because the air is cold and hard to remove heat from. The colder the air, the harder it has to work, resulting in large inefficiencies at low temps. If you have mild winter temps, then it will be fine. Do you need summer cooling? If not then a small hydronic boiler would be cheaper to install and operate. I just bought a very nice used boiler for a client for $500. Everyone is upgrading to high efficiency, so the 80% efficient models are available at low prices.

Thanks for the reply Bill!

Sadly we can't get gas on the site so a hydronic boiler wouldn't be an option

I've been doing a bit more rooting about for pumps and there's a few that we could use to heat the system water directly.

Has anyone had experience with Duratech Dura+ pumps? They appear to be designed with winter usage in mind. Some folks over at a Koi forum seem to rate them.

There's a 10Kw Duratech Dura+ that sucks 1.7Kw of juice and is rated for heating a system of 40m3 down to -15c.

We have a system volume of about 13m3 which is constantly circulating. It's a sump based system with a single pump that splits the supply in two and feeds the fish tanks and grow towers ala Bright Agrotech.

We're thinking of hooking the heat pump up to the sump tank, so that both the towers and tanks are fed with warm water.

Regarding the location of the heat pump, does it need to be exhausted outside? The tunnel is far from airtight.

Here's a mock up of our system:



Would it be worth trying to raise the heat pump to the top of the tunnel? Hot air rises n'all that?

Cheers!

Sean

Well that's too bad Sean, although heat pump technology has come a long way since I was installing and servicing them in the '90's.
If you don't want it to get really cold in the tunnel, I would recommend placing the evaporator outside. A heat pump is just an air conditioner running backwards.
You must balance the system that you install; meaning that the coils should be approximately balanced with the output of the HP, so the unit will not short cycle causing loss of efficiency and reliability. The other thing is air and particulate removal, for this I would recommend installing a hydronic separator(Caleffi makes a great one).

Air source heat pumps have changed completely in recent years. You can find mini-split products from Mitsubishi that approach the efficiency of ground source heat pumps. It's a real game-changer.