Heating a 125 gallon cistern

[894tom]

Hi, I am usually over on the PV end of things in this forum but I have a question about heating water with solar. I will get right to the problem. In the summer I have a condensation problem. My cabin temperature gets to around 80-85ish but the cistern in my attic loft still needs to be refilled with water every 3 or 4 days. I begin pumping the well water (47-50 degrees) into my cistern. An hour or so after filling up the cistern, I have a big mess (condensation) I was thinking preheating the water just before it hits the cistern would solve the issue.

Some notes on the cistern and its set up. It is a 125gallon water tank purchased from a local tractor supply chain and sits in the loft area of the cabin which will cause it to be room temperature (80-85). The area the cabin is located about 2000' ASL. The air is almost always dry.

Idea #1. I have a 120v 30amp POU water heater that I have been considering installing as a preheater. The POU water heater is only capable of raising the water temp 14-15 degrees. If I pump first thing in the morning, the cabin temp in the summer is around 70-75 degrees, so I may not have a problem with condensation at that time using the POU heater. In the winter, the cabin temperature flucuates between 65 and 75 degree max temp. It can be even colder in the AM before I crank the fireplace back up so I have no problem with thinking the POU water heater will work fine in the winter months.

Idea #2. I believe someone once suggested to me that I insulate my cistern. I like this idea because its an affordable option and requires no additional energy usage....BUT I was thinking I would still have condensation issues with the PVC pipes inside my sheetrock walls for several hours after the refill occured.

Idea #3. Solar preheat. This would require a refilling on sunny days only. I have no idea if a solar water heater panel(s) can preheat 47-50 degree water to 80-85 degrees in one pass when I am pumping 5gpm in the cistern through 1/2" pipe.

I am ready to sheetrock the interior of the cabin and would like to do any additional plumbing (if nessasary) prior to the sheetrocking.

All ideas and suggestions welcome.

[Naptown]

Put insulation and a vapor barrier on the tank and pipes feeding it. There is no way you are going to heat the water that hot (although you only need to get the temp above the dew point when pumping) with solar at 5gpm. Well you could but it would be cost prohibitive.

[inetdog]

Put insulation and a vapor barrier on the tank and pipes feeding it. There is no way you are going to heat the water that hot (although you only need to get the temp above the dew point when pumping) with solar at 5gpm. Well you could but it would be cost prohibitive.

You can either use an open cell foam insulation of the type sold in hardware stores for insulating pipe and then seal the seam with tape to make a partial vapor barrier or use closed-cell foam, glue the joints and tape them to provide a better vapor barrier.
Since your goal is to prevent condensation rather than retain or reject heat, you must include some sort of vapor barrier in your insulation, otherwise the condensation will still take place on the outside of the pipe, just inside the insulation.

Loose fiberglass insulation, or insulation sections which are not sealed, will still allow condensation on the pipe and will result in soggy insulation.

For the cistern, again the critical point is not the insulation alone but the vapor barrier. One way to get both in one application is to use a closed cell spray foam, but that may not be easily accessible for DIY. Spray foam would also be an alternative for the pipes themselves inside your walls.

The only way that solar heating could provide enough heat fast enough but still economically would be use use it to heat the water in a tempering tank which is located outside. The incoming pumped water would go into that tank and would mix with the solar heated water, hopefully keeping the temperature on the inside piping above the dew point temperature for the duration of one pump cycle.

But unless you want to have heated water in your cistern, you would have problems regulating the tempering tank temperature to produce output which is above the dew point but still not too warm or even hot.

[russ]

1) Do not use open cell foam - use closed cell only to stay away from the soggy Dave mentioned.

Something sounds strange - Is this an experienced problem or one you think you may have? All well water enters the house at maybe 55° F and others (including myself) don't experience this.

[MikeSolar]

1) Do not use open cell foam - use closed cell only to stay away from the soggy Dave mentioned.

Something sounds strange - Is this an experienced problem or one you think you may have? All well water enters the house at maybe 55° F and others (including myself) don't experience this.

I have seen some well water come in a lot cooler mainly because the the well is fed by an artesian spring so it is possible. Does the tank have a sealed top or is it a pressure capable tank?

[russ]

Mine is closed (pressurized) within the house. I pump from the well into a 35 cubic meter storage where the water is chlorinated. It then passes through a softener and the pressurized system.

His could be closed within the house as well - just vent it to the out of doors.

[894tom]

1) Do not use open cell foam - use closed cell only to stay away from the soggy Dave mentioned.

Something sounds strange - Is this an experienced problem or one you think you may have? All well water enters the house at maybe 55° F and others (including myself) don't experience this.

My cabin is located in central NY. Its on top of a mountain. My well is 275ft down and the water coming in does come in at the temps I described. I have a 110/220v genny that pumps the well water into the open cistern (no pressure) I have a small pump inside the house that supplies pressurized water to the cabin from the cistern.

No this condensation problem is an actual problem...not a possible future problem. I found a link for a closed cell DIY spray insulation. I believe this is going to be the route I take. The downside on insulation is there will be colder water to heat with my on demand propane water heater.

In case you were wondering...yes I thought of running the water through the propane water heater while I fill up the cistern. On another note, I have refilled the tank when it was about 50% empty. The room temp cistern water seemed to be warm enough to stabalize the condensation problem the incoming cold well water causes by noon.