Backyard Aquaponics
A place to discuss aquaponics

Hey DD..... I have read through this thread a few times now, and I'll be the first to admit that I don't really understand the finer details about some of the discussions going on here, but I'd like to understand... So could we please just take a step back for a minute, and look at the big picture...

Now forgetting the whole idea about how you go about solving this problem, isn't the big picture related to the cold conditions that you have over where you are, and trying to create conditions that will be more acceptable, hoping for all year round growth..?

If this is the case then I propose a slightly different slant on the solution, that I hope is more simple.. You have a house that is warmed by watever means, your interior and basement is warmer than outside.. Your fish tank is a fantastic thermal mass. Can't you look at attaching a greenhouse to the side of your house to contain the AP system..? Now ok, this really needs to be double skinned and preferably bubble filled in winter, reasonably do-able without too much effort.

The thing I see is that most plants like warm conditions as well as the fish.., And gravel filled growbeds can act as great thermal mass that heats up during the day and hold that thermal mass during the night, as well as the water... You could then look at sapping some of the heat your system needs from the house, through the basement or where ever by way of ventilation...

I guess the point I'm trying to get across is, that I see this whole idea of trying to seperate the greenhouse from the house, and keep heat in one area different from another being counter productive... Most of your plants will prefer a warmer environment, and if you were to spend the money you were thinking about spending on head exchangers, instead on a more thermal efficient greenhouse, then you solve the problems....

You could install small fans that radiate house heat into the greenhouse when needed, and then in summer you caqn open the greenhouse up and reverse the fans, sending cooling air into the house...

Spending money on a thermal efficient greenhouse is only going to save you money in the long run... Look at the Speraneos, they run their greenhouse all year, without heating, while there's a foot of snow outside, and they have tilapia inside, by using efficient designs and thermal mass....

Now I may be way off the mark, but is it a thought?

I understand EB, and that is the thinking I have been planning on using this far. This is just an idea I'm wondering about as a bit of "lateral thinking".

I was thinking along the lines of a used freezer from the local freecycle group, with the coils reconfigured, to keep the costs in line with the rest of the hardware.

Thanks everybody for the input!

Dave, my system starts now. First 8 plants yesterday and fish in a couple of weeks. Next winter I will be attempting having plants all winter with almost no supplimental heat. In late Jan and early Feb we get very cold and low lite. That will be my experiment. But my fish can live under a crust of ice, so I have less of a challenge. My greenhouse is very well insulated and shares two of four walls with my heated shop building. We will see what happens.

To me it is important to use very little energy and adapt my system to what is possible under those terms.

Just had a rush of blood to the head are american roofs like ours because every time i go into our roof space ite always hotter than outside IE heat always travels up so why not lay a roll of black polly on the celing joists and pump your ap water through that with temp sensers controlling the pump!

F&F, attics are hot in summer, but not winter. Our attics are well vented to handle summer heat. This could bring the water temp up faster in spring. A check valve would be needed to stop heat loss at nite.

My plans were for a greenhouse with a roof that somewhat matches our house's which is a steep Cape Cod. With a steep roof I would put solar water heating gear up in the roof volume.

Dave, in attic or on the roof?

Hey DB,
I was thinking of black panels in the space between the ceiling and the peak, angled more or less versus the roof's slope, depending on the season (steeper in Winter, shallower in Summer (I guess I wouldn't need them in Summer, heh)). I guess that would mean in the attic.

Dave, I think that might be a problem. Why change the angle if it is in the attic and not in sun lite? On the roof the angle change would cause the sun lite hit at close to 90 degrees and lose less to reflection(works for photo voltic as well). Am I missing something? Is your attic hot in winter?

I have a dehumidifier that I got for free from the neighbor's yard sale a couple years ago, that I am going to tear apart tomorrow, if it still works. I also stole two Mac G5 CPU "radiators" from the recycling at work, not sure if they are from the liquid-cooled or air cooled Macs, they have sealed copper tubes going up into the aluminum stacks; basically repeating aluminum plates in a big stack. These will be good heat exchangers.

Did some calculations tonight for interest:

4184 joules to change 1L water by 1 degree C (4.184 joules per calorie, 1 cal changes 1mL by 1C)

So if I wanted to heat 40 gallons/160L by 13 degrees C (40F to 85F, equalized first to 62F/16C), I would need 4184 x 160 x 13 = 8702720 joules

1 watt = 1 j per second, 3600 seconds in one hour

8702720 joules / 3600 seconds = 2417 watts for one hour to raise 160L by 13 degrees C (this is heat energy)

Heat pumps have a coefficient of performance >1, which means you get more watts of heat moved than the watts of electricity put in. Commercial heat pumps can have COP of 3 or 4, so the heat watts can be divided by this to get electric watts.

2417 watts (heat) / 3 (COP) = 805 watts electricity for 1 hour

If this cycle is not happening all day long, say six times per day:
805 watts for 1 hr x 6 cycles per day / 24 hours per day = 201 watts continuous equivalent. So it would be like having a 200 watt light on all day long to cycle 960L (160L x 6 cycles = 960L) of water per day between the fish and plant zones.

This would be the largest temperature delta; when the weather is warmer then more cycles can happen for the same electricity per day or the same cycles would take less electricity per day. If this would keep me from running a 400 watt MH grow light for 12 hours per day then I can break even on it.

Saturday is experiment day!

I teased the hot and cold parts apart and I'm going to measure what kind of heat difference I can get out of this dehumidifier. The water temp according to my digital fish tank thermometer is about 44F/6C, I'm going to wait for the water to warm up for an hour or so before running the test.

Results for today are in:

18gal/68L, ran for 45 minutes, "cold" tub went from 44.7F/7C to 39.4F/4C, "hot" tub went from 44.5F/7C to 59.5F/15C. A spread of 20F/11C. The cold heat exchanger was iced up, and I started swishing the water around to help dsitribute it better. The starting water temp was lower than the design, and I stopped running the compressor for about 15 minutes - the test took 1 hour. For the next experiment I will put insulation under and around the tubs, start with warmer water, and run for 1 hour nonstop. Also the water will be swished around to keep the energy transferring efficiently.

Mwaaa haaa haaa!!! The mad scientist is at work.

Just don't electrocute yourself!

DB, I reread your post and I finally understand what you were talking about with the roof. I am planning on having the roof entirely see-through - so the solar panels in the attic will be lit up, not shaded.

DD just a couple of suggestions If the air temp is higher than the cold water temp you may get more efficiency by leaving the cold side of the dehumidifier out of the water and put a fan blowing on to disperse the ice.
another way to get more heat output is to have running water in your cold tank
the compressor produces the same amount of heat while running so the hotter the gas is when it enters the the compressor the more heat you will get out of it
one thing you have to be aware of is that the compressor relies on cold gas to cool the motor and prevent burn outs
in saying that one thing you can do is build a heat exchanger to collect the heat as soon as it exits the compressor.
this will add approx 20% more efficiency to your system and considerably reduce the head pressure within your compressor
hope this makes sense to you.
tomo