Here are a few notes on climate control...
First of all the reports that reef tanks thrive at 82F are absolutely true. I aim for 80F because it is the easiest value to maintain without using any additional resources/energy (heaters & chillers). Once you plug in all of your equipment, the tank will level off to about 79-80F. It would require the use of one or likely more heaters to maintain 82F, so I go with the flow and settle with an easily manageable 80F. If you have a chiller, it should be set to come on at 84F as basically a fail-safe. Heaters should bet set to come on at 79F to maintain consistency. If you set your system operating level to 82F, it leaves a little less room for temperature climbs. A target temp of 80F leaves room in both directions for error.
For a large system like Peter's, I would use an inline titanium heater run on the main controller. Sump heaters tend to degrade due to salt exposure in the seals and wiring. They also take a bit of a beating during water changes and servicing as they are left on while exposed to air. I use a piece of styrofoam to make a float for the top of the heater so it can float in the sump, keeping the sensitive parts dry (suction cups don't last long in salt water). The heater(s) should be located in a part of the sump where the water level is constant. The styrofoam floats will allow the heater to follow the water level, should it fluctuate. I would focus my attention on climate control of the ambient room temp with air conditioning or a furnace/boiler, and save aquarium devices in-line or in the sump for fine tuning.
While I would never talk anyone out of a fail-safe device, you have to remember that everything you plumb into your system could potentially leak, and everything you plug in could potentially cause stray current or shock/fire hazard. I don't use chillers as a general rule. It's part of the K.I.S.S. (keep it simple stupid) or "less is more" approach.
The factors that influence system temperature are as follows...
1) Ambient room temperature: North American homes are warm in the winter and cool in the summer, thanks to our desire for convenience and comfort and with a little help from huge utility bills
As a matter of fact, many homes are warmer in the winter than they are in the summer, and cooler in the summer than in the winter. Typical ambient room temperature is somewhere around 72F (for the record, we use metric in Canada).
Working with 72F, we can assume that still water will reach equilibrium with that temperature. Once you start moving the water it has more contact with the surface where the temperature reaches equilibrium. A cooling effect starts when surface water evaporates and takes with it heat. Evaporative cooling is a very important process that we will discuss later.
2) Aquarium location: This factor is directly related to the ambient room temperature covered above. An aquarium located in a basement, or with a sump in the basement or garage will run cooler than an aquarium in an upper floor of a house. Even the position of the tank with relation to the floor makes a difference. While I operated a tropical fish wholesale warehouse, I found that the three levels of tanks showed different temperatures. The freshwater tanks where not on an open system, just air-driven sponge filters. I heated the warehouse to 80F, but the bottom tanks 1' off of the ground were 74F, the middle row 3' off of the ground were 76F, and the top row 5' off of the ground were 78F. Peter's radiant floor heating will eliminate this heat gradient issue. Placing the sump directly on a concrete floor will offer cooling.
3) System volume: Having a large sump is a cheap and easy way to improve thermal dynamics if you have the space. The extra system volume will also improve water quality, as the saying goes "the only solution to pollution is dilution". The best solution is actually filtration, rather than sweeping the problem under the rug, but it doesn't rhyme so I doubt it will ever catch on
Saltwater has greater density than freshwater, so it holds its temperature longer. Large tanks (over 200 gallons) are particularly stable with little or no fluctuation caused by day/night ambient room temperature shifts. In other words, the room may be cooler at night, but the tank will stabilize at a compromise temp somewhere between the day & night temp. The large thermal mass of a big tank makes quick temperature changes up or down more difficult, but nature doesn't like change, so overall the thermal mass is a good thing for stability. Remember that bleaching incidents on natural coral reefs has been noted after only 2F temperature increases. This doesn't mean a 2F increase in temperature will bleach (expelling symbiotic algae/zooxanthellae) or kill corals, but it does underscore the necessity for stability.
4) Heat transfer: Every electrical device, including chillers add heat to aquariums. Add a few degrees for pumps, a few more for UV sterilizers and a lot more for lighting and your cooler than room temp tank is suddenly 10F hotter. Some of this heat is unavoidable, but most of it can be at least minimized. Directing a 12" circulation fan perpendicular toward the display or sump surface will drop the temp 5-9F. The evaporative cooling effect will tax your top-off system a little more so make sure you can keep up with the demand. A second fan can be used to blow across the surface of the water, pushing radiant heat from the light away from the water. Raising or lowering the lights will also influence heat transfer.
Venting the cabinet or filter room is an often overlooked detail of climate control. Some pumps don't employ cooling fans and subsequently run at very high temps (130-140F). This is not a problem if the heat is allowed to vent away from the system, rather than trapping it and raising the ambient temp and surface water temp. Chillers are an important device to vent as the heat exchanger will dump that heat right back into your system so it works against itself.
5) Water movement: As mentioned in the previous points, good water movement will increase the amount of water exposed to the surface for thermal and gas exchange. A good system of flow dynamics assures that water is moved from the bottom where it is cooler an d lower in dissolved oxygen to the surface where it can be oxygenated and heat can vent. Using a glass top will raise the temperature about 5F. While this is rarely desirable, it's a good practice if there is an extended power outage and your back-up power is limited. I assume Peter has a natural gas generator and UPS/deep charge marine battery backup. Certain filtration devices (gas reactor, wet/dry filter, shallow ATS etc.) work as evaporative coolers or cooling towers. In general, these evaporative efforts are directly connected to improved gas exchange as well.
6) Air quality: Fresh, dry air will be cooler than stale humid air and gas exchange is more efficient. Peter's HRV unit is more than enough to handle this issue. It also vents equipment to deal with heat transfer.
been wondering about cooling heating issues lately as im getting 2 250w MH for my 75g tank (90g total system) build. also thought id mention the guys at my local petco think all water movement should be created by HOB filters LMAO. whats even more funny is i know a dunce that believed them.
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