Larry Lunsford

Some of you may be as fish crazy as I am - I not only have a Koi pond, I also have a salt water aquarium. My reef requires regular additions of purified water (water with nearly no minerals or other impurities) to make up for water that is lost to evaporation. Purified water is also used to make new salt water for water changes. My pond also requires topping off to replace water lost to evaporation, but it doesn't require that the water be ultra pure (it actually needs the minerals in tap water).

Besides needing good water chemistry, my reef also needs a steady temperature. This summer has been hot and my reef has needed cooling to stay at its desired temperature (I don't have air conditioning).

To make purified water, I have a water purifier (of course!). It's a 4 stage unit with: sediment filter, activated carbon filter, reverse osmosis (RO), and de-ionizing cartridge. The RO chamber not only produces filtered water, but it also makes a lot of waste water (about 5 gallons of waste water for each gallon of purified).

One day while putzing around in my basement shop something struck me - a drop of water that had condensed on my main water supply pipe. I had my water purifier running, and the steady flow of cool water was creating condensation on my pipes. Something else also struck me - I could harness the cooling of the supply water to keep my reef cool.

My new water system is shown in the diagram below. Water coming in now serves three purposes. The cold water from the main passes through a heat exchanger in the sump of my reef to provide cooling. The water from the main then goes to the purifier. The purified water is used for the reef, and the waste from the RO goes to the pond. This system wastes very little (I still need to find a small water powered generator so I can make electricity from the pressure of the tap water).

The waste from the RO is better for the pond than tap water since its been run through the activated carbon which removes harmful chlorine. It's also warmer (since it got warmed up by the reef) which is good too.

My system consists of a 4 stage purifier plus: extra stage of activated carbon filtering, insulation, heat exchanger, solenoid valves, and temperature controller.

I added a second activated carbon filter as an added measure of insurance against allowing chlorine into my pond. I test the water out of the 1st activated carbon filter and at the first sign of chlorine, I change filters. When changing filter cartridges, the old 1st stage gets tossed, the old 2nd stage gets moved to the 1st stage, and the new cartridge gets put in the 2nd stage. This way, I always have a fresh 2nd stage activated carbon cartridge ready to handle any rogue surge of chlorine that may get past the 1st stage. This cartridge change scheme also lets me get the most out of my cartridges since I don't have to change them until they're fully used. The slow flow of water through the purifier also allows the activated carbon cartridges to do a good job of filtering chlorine.

To preserve as much of the cold in the main line as possible and to prevent water condensation and dripping off my supply pipes, I insulated the cold water supply pipes in my house from the water meter to the heat exchanger. I used foam insulation that's available in most hardware stores and it just snaps onto the pipe.

The heat exchanger is a coil of 1/4" plastic pipe that has been placed in the sump of the reef where a lot of reef water passes over it. I made a coil form out of clear acrylic to make it look nice, but it's not necessary. The plastic pipe is the same stuff sold for connecting your ice maker (typically 25' in a hook-up kit). You can also get longer lengths at plumbing supply stores or better home improvement stores.

The solenoid valves I use are those made for sprinkler systems. They're cheap, easy to find, and easy to connect to. You could also use a solenoid made for a washing machine or dish washer.

The temperature controller may be simple or elaborate. The simplest controller is just a timer set to turn on the water at fixed time(s) every day. You can get mechanical timers for less than $10 at Wal-Mart or any hardware or home improvement store. Since I'm using sprinkler valves, I am also using a sprinkler controller. You can find sprinkler controllers that are cheap, but which also give you easy control over the valve timing.

Cost Of Cooling: My home made cooler is cheap to build and cheap to operate. It cost about $75 to build my cooler (2 solenoid valves at $12 ea, 100' plastic tubing $10, sprinkler controller $30, misc pipe fittings $10). A cheap water chiller would have cost at least $600. The cost to operate my cooler is nearly 0. I need to make purified water for my reef, and the time I run my cooler works out to be the same time I'd be running the purifier anyway.

If you're considering buying a chiller or making a tap water cooler and just wasting the water, use the formulas below to calculate operating costs. Formulas give BTUs per dollar. For the chiller, I used figures from a recent magazine ad (1/5hp chiller, 2400BTU/hour, 120VAC, 3.5A).

Here's a diagram of the system:

Here's some pics of the cooling coil construction:

Tap Water Cooler:

BTU/$ = (T1 -T2) * 8.4 * 1000 / W

T1 - Temperature of Reef (° F)

T2 - Temperature of water main (° F)

8.4 - Weight of water (8.4 pounds per gallon)

1000 - Units of water (most cities charge for water by 1000 gallons)

W - Cost of water (dollars per thousand gallons)

In my case the cost is (80 - 65) * 8.4 * 1000 / 5 which is 25,000 BTU per dollar.

Electric Chiller:

BTU/$ = 2400 / ((120 * 3.5) / 1000 * E)

BTU/$ = 5714 / E

2400 - BTUs per hour of small chiller

120 - Voltage rating of small chiller

3.5 - Amperage rating of small chiller

1000 - watt hours in kWH (utility companies sell electricity by kilowatt hour)

E - cost of electricity (dollars per kilowatt)

For me, E is $.08, so running a chiller would give me 71,000 BTU per dollar.

If I needed a lot of cooling and was just going to dump the water cooler water down the drain, I would be better off in the long run (very long run actually) to invest in a chiller.

Figuring Cooling Requirement: One BTU (British Thermal Unit) is the amount of energy needed to change the temperature of one pound of water by 1° F. Water weighs 8.4 pounds per gallon. To change the temperature of one gallon of water by 1° F requires 8.4 BTU. To figure your daily BTU requirement, multiply gallons of water * 8.4 * temperature drop. Include sump, refugium, etc. in water volume - don't deduct for rocks and sand since they need to be cooled too. In my case my cooling need is:

120 gal (100 gal tank + 20 gal sump) * 8.4 * 6° F = 6000 BTU/day

To get 6000BTU/day with the water chiller costs 6000/25000 = $.24/day.

To get 6000BTU/day with the electric chiller costs 6000/75000 = $.08/day.

I need to run my chiller for about 60 days in the middle of the summer. An electric chiller would save $9.60 per summer if I were just dumping the water. At this rate, it would take approx. 50 years to pay for an electric chiller.

Koi