Will this work in my evac system?

rt_2

A little background. I live in NH. I have a solar evac tube system. 50 tubes in all. I have a 80 gallon indirect water heater used as a storage tank. This tank heats my domestic hot water. I typically shut down my system when I snowbird in FL for 4 months by covering the arrays with a tarp. I leave my house thermostat at 50 degrees F. What I was thinking about doing was installing a 50,000 BTU water to air heat exchanger like this: http://www.outdoorfurnacesupply.com/uh50.html?CAWELAID=520011210000000907&CAGPSPN=pla&catargetid=520011210000000001&cadevice=c&gclid=CKSH-vSZ8MYCFUuRHwoduasFog#
I would bypass the storage tank and all the solar heated glycol would pass through this heat exchanger and would be used to raise the temperature of my basement a little. I would wire the fan to the circulator pump so that it will start when the circulator starts. Will this work? The only concern I have is will the heat exchanger extract enough heat from my closed loop system to prevent the temperature from continuing to rise and overheating my system or will it remove enough heat to keep the temperature at bay? I'm wondering if for example, if the liquid entering the exchanger was 125 degrees F, what would the temperature be exiting the exchanger?

rt_2

I guess no one has any experience with this. Thanks anyway to all who at least read my post.

hot_rod

Sure that would work fine, what type of controller do you have? Some models have a second function that could turn that on.

Another option would be a 3 way diverter, the DHW tank heats first, any excess goes to the heater.

Myson used to build a SolarVector cabinet heater. Collector directly to the heater, no DHW.

You may as well use the energy.

rt_2

Thanks for your response Bob. First, the heat exchanger fan would be wired directly to my circulator so that when it starts the fan will also start.
I'm going to bypass or maybe just drain the DHW tank. I'm not going to be here (will be snowbirding in FL) so there's no need for hot water. All the heat/hot glycol will be going directly to the heat exchanger.
My biggest concern is that will this heat exchanger remove enough heat so that the loop temperature doesn't continue to climb.

hot_rod

Currently the sensors that turn on the circulator are located 1 on the roof, and another in the tank #2. So when the tank temperature drops, the pump starts.

You would need to move that tank temperature to the heater, or get a control that has two outputs, many of the newer solar controls have multiple functions. Or else you do not have a means to trip the pump on, sensor 2 is just watching the DHW tank temperature.

I think that should be plenty of coil to remove winter energy from that array , just let it run whenever the sun is out, no need for a thermostat, I doubt it would overheat the space.

If you want exact numbers, look up the brand and model of your collectors at www.srcc.org. Upper right hand box shows the collector array under different sun, and temperature conditions. Compare that to the coil output at the expected temperature.

Since you have already invested in the solar system, it would be wise to put to work year around. An air handler and some piping and control work is all you need.

No sense in covering up a collector that has work available

rt_2

Thanks Bob,
I'm thinking that I could just leave the sensing probe in the DWH tank. It will sense cold all the time and the differential temperature will start the circulator. When the loop temperature at the array gets to 6 degrees within the temperature of the tank, the circulator will stop until the temperature increases at the array. I could remove it and put it next to the exchanger but I don't see any advantage. I could be wrong. The temperature of the water in the tank would be a around 50 degrees all the time. The temperature in my basement would be about the same unless this process raises it.

hot_rod

Are you putting the fan coil in series with the DHW tank coil? If so you will need to be able to bypass it for summer use.

Typically these systems are piped with a 3 way valve, similar to how a coil is installed for summertime heat dump.

We need to see what your thinking is for piping the coil.

Your's would be wintertime heat dump.

Here is how Apricus shows piping in a dump zone.

rt_2

I'll have the fan switched so that I can shut it off in the summer. As far as the exchanger, the intake to the exchanger will come from the pipe before the DHW heater coil and the outlet from the exchanger will tie back in the the outlet side of the DHW heater coil. There would be a valve on both the intake and the outlet of the exchanger so they can be shut off in the summer and another valve will be installed before the coil of the DHW heater coil. This valve would be opened during summer time use so the hot solar heated glycol goes thru the DHW heater coil.

hot_rod

Sure that would work, good to have a bypass, even a manual one.

Some of those fan coils have adjustable fan ON switches. Bypass that if you want the fan to run whenever the pump does.

Check the rating on your solar controlled to be sure it can handle both the pump and fan. Most of the electronic controllers have a 1A rated relay.

Use the solar temperature down as low as possible. Squeeze all the heat out, and drive collector efficiency up with the coolest possible return.

rt_2

I ordered the heat exchanger tonight and it should be in by Friday. Will install it next week some time. Will let you know how it works out. Thanks for all your help Bob.

rt_2

Boy do I feel better. I installed the H/E (heat exchanger) yesterday and got to try it today. It works awesome so far. The highest temperature the array got was about 148 degrees F. The fluid temperature going into the H/E was about 143 degrees and exiting the H/E, it was around 130 degrees. The air going into the H/E was 80 degrees and the air coming out of the H/E was just about 102 degrees. The sun was out a good part of the day. A few clouds from time to time. I'm going to shut it down and wait for another day when it's suppose to be really sunny all day with no clouds at all and test it again. My biggest concern was that the H/E would not extract enough heat from my closed loop which would allow the array temperature to continue rising to a unsafe temperature but it did just the opposite so far. Knock on wood. Yeaaaaaaaa!

hot_rod

Near perfect numbers. Good win.

rt_2

Had a great solar day today in NH and ran a test all day. At the days highs the array temperature went up to only 141degrees F, the fluid going into the heat exchanger was about 137 degrees F, the fluid exiting the exchanger was 128 degrees F, the air going into the exchanger was 74 degrees F and the air leaving the exchanger was 100 degrees F. I'm so happy. It's working great and better than I expected. My array is at a 44 degree angle so I'll try another test sometime in October or November when the sun is hitting the array more directly.