Backyard Aquaponics
A place to discuss aquaponics

I had AP insomnia again last night.

Does anyone know of a DIY way to make a heat pump for AP water, to say move a barrel of fish tank water at 85F/29C to an ambient temperature of 40F/4C and transfer this heat to another barrel of returned water (from a cold greenhouse) to put it back in the fish tank at 85F/29C again?

Hack up a used refrigerator or something? Car air conditioning compressor?

Not sure if I follow you Dave, what are you trying to heat with the fish tank water?

I'll wait for clarification on GF's question then i'll comment

give us the exact application as close as you can water volumes and temperatures involved and the time frame you wish it to be transferred in and i can give you the required amount of KW (HP) that the heat pump will be required.

Refrigerators are generally quite small in power, as all they have to do when at temperature is remove the heat that transfers through the very well insulated case.

What you want to do is quite do-able, but you'll probably need the services of someone to modify the pipework, evacuate the system, and re-gas it.

Keep in mind, that you only need to use a heat pump (in refrigeration sense) if the temperatures are such that heat would not flow naturaly, IE warmer "ambient" than what you want to cool to. otherwise a water / brine / glycol system through heat exchangers would work fine.

Oops, i was going to wait to comment?

Steve

Ya get that! steve

I want to transfer the heat from warm fish tank water down to the outside ambient temp. The heat that is moved will heat up return water from the outside. The cooled water will go outside, and the warmed water will go back into the fish tank.

I would like to be able to transfer the heat from one 50 gal/190L barrel to another, say within 1 hour. The temps I am thinking about are posted above. I'm late for work!!

DD, i'm sure its just me that can't seem to grasp the concept.

It sounds like you just want to warm the cold green house return water to the fish tank.

Why would you want to drop the temperature of your fish tank to 4C?

I first assumed to wanted to "pump" heat between water volumes.

What it sounds like you need is a heat pump that simply heats the retun water from the green house as it comes into your fish tank?

it is pointless taking the heat from your fishtank to put back into your fishtank. Just use a standard reverse cycle AC system. An old room AC (box type) could be modified. outdoor coil is fan forced with air inside coild is immersed in water.

Am i way off track?

Hi Steve, I know you're the man for this discussion so I'm glad to have someone already here to bounce this off of.

The idea is that rather than try to keep a greenhouse at tropical temps when the outside temp is well below freezing, I would use some electricity to remove the heat from the water before sending it out. Not really removing it but transferring it to the return water.

I am thinking of two barrels, with a compressor in between, that transfers the heat from the one into the other. Warm fish tank water would be pumped into the one barrel, cold greenhouse water would be pumped into the other barrel. The heat pump would then run for an hour or two to transfer the heat out of the one into the other. Then the water is pumped out of the barrels, outbound cold one to the outside and the inbound warm one back inside.

The idea is to decouple the nitrogen cycle and nutrient removal into two loops. I would do this 50 gallon water transfer several times per day, the nutrient removal would happen in these batches, rather than continuously. The inside would have a separate biofilter running all the time to do the nitrogen cycle.

The idea is that if my outside water is at the ambient temp I will not have to worry about heat losses outside at all. I could use essentially a cold frame, and just keep the beds temps where I need them for not-too-slow plant growth rather than keep them at tropical temps for the tilapia.

If I was just sending out warm water it will come back with most of that heat lost, unless everything single thing in the greenhouse is insulated and designed for temp maintenance. Then I would have to have some very powerful heaters to bring it back up to temp, and bring it up non-slowly. The aquarium heaters I am using would take hours to heat it back up and would use thousands of watts to do it.

If the water heat were instead transferred during the water exchange between the inside and outside then I am assuming that this would use less power.

If I took the water down to 40 degrees and the sun came out while the greenhouse water was circulating and it came back inside a couple hours later at say 50 degrees then I would need less power to bring it back up to temp as the day got warm. It would be like using the greehouse gravel as a geomthermal mass. During the night I wouldn't transfer the water at all.

ok, i think i get it, just let me read over it again tomorrow arvo (afternoon ) its nearly 1am here.

OK, but don't get AP insomnia over it!

Intresting Dave, You want to have two seperate bio filters then, One for inside and one for out? But because you dont want to loose to much heat from the fish tank you'll keep the two system waters seperate?
Am I understanding it so far?

Hi GF, just one biofolter in the basement, looping water for the fish. The plant water would be a separate loop, transferring in batches on some kind of timed schedule. I imagine that in the greenhouse would be a sump/reservoir, and the water would be circulating continuously among the plants and back into the sump. The water that goes back into the house would be pumped from the greenhouse sump, be heated back up, then go back into the fish tank. It would be like me doing a 50 gallon water exchange every couple of hours.

OK so the water being pumped up to the green house would have to intermix with the fish water in order to get the nitrates? Or would the green house water just be for keeping the plants warm in winter etc?

The water in the greenhouse would be fish water, but cooled down. It's all one water supply, but there is a temp change between the inside and outside. You could look at it as the batch of fish water adds nutrients to the greenhouse water, and the greenhouse water dilutes the fish tank water, if you want to look at it that way.

Ok thanks for the in depth now for a low cost sensible solution. mmmm Steve where you at?

Right - it would have to be from a reused something or other because I have no budget for it! I joined the local "freecycle" group, I'm hoping to see if anyone has a used refrigerator they want to get rid of.