drain back solar
 

I thought I would chime in with my drainback tank project. it is part of the ASHP that will replace my Viessmann boiler. First thing I did was to rip out the forced air from the house and replace it with floor heating in light weight cement and old cast iron rads where I couldn't put the floor heating. That was 5 years ago.

Now I am putting in a few more rads to drop the water temp needed to heat the place so that a Hp can be used. I would like to be able to heat with no more than 40C (104F).

Here is the pic of the tank I made out of PP and spray foam (don't do it this way, it was way too expensive)


Then, I got the innards from a German tank maker called Rotex. The tank was a display model with a big hole in it but the HX were intact. There is a HX for domestic hot water which takes the heat from the drainback tank as needed, one for the solar (at the bottom), one to go out to the house for heating and one for a backup boiler.

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I will be putting the wall solar heat on to the solar HX, the boiler will stay put as a back up, the HP will heat the tank directly to keep the losses to a minimum and hopefully the DHW will work OK. I have only heard of these tanks before and never seen one in action so we will see.

Interesting tank setup. Can't wait to hear more. What else are you planning?

nice project Mikesolar. I'm adding solar preheat to my "outdoor" shower (it's actually indoors, but in a separate building, so ... long story) next spring. I look forward to more details. Especially how the unit exchanger works. I would be interested in seeing more pictures of the guts.
Good luck. And, expensive yes, but nice looking tank.

Any updates on this project?

not yet. I'm working on building the heat pump but I am short the heat exchangers. My normal supplier doesn't have the right size so I will have to go with a different make, probably SWEP. I am waiting for a bit of good weather so I can start putting up the insulation on the brick before the panels get made. So much to do.

In the mean time, our first PVThermal panels are going up. I am retrofitting 5 rows of 8 (250w ea) on the roof but the snow and ice made it too dangerous to get up there. 3 rows are done but it will take more time. bummer.

PVThermal? Perhaps you could explain the whole setup?

As a PV panel get warmer than its 25C test temp it looses about .4% efficiency for every degree increase. Panels can reach 80C or more at full sun and hot weather so given the same solar insolation (1000w/m2, for example) a 250w panel will only put out 195w which is quite a drop. We have designed a heat exchanger for the back of the panel that removes the heat and in our 10kw system, the heat is being put in DHW tank and what is left goes in the swimming pool. We hope to sell it online as a kit to retrofit existing panels but we are not at that point yet.

The system will also be used, eventually, with the air source HP that we are working on but that is a year or so away. The goal is to be able to install an ASHP and solar thermal for much less than a GSHP and get the same annual COP. Plus, the thermal will provide free DHW for the summer months.

Bit of a tall order but I like a challenge. I only wish I had the programming skills of some of you guys.........

Looks like a great project. The drainback system on my house works well, except for the noise from water draining into the drainback holding tank. Seems to be getting louder with age. It's a 13 gal tank on the second floor behing a closet. When I get some time I plan on adding a diffuser nozzle at the tank entry.

Good luck on your project, looks promising.

Do you have a vacuum breaker or auto air vent on the roof? If so, you could have some steam escaping and being replaced with air which could eventually cause you to lose some liquid.

I don't have a vent or vacuum breaker on the roof. It is a closed system with a programmable controller. I start the pump at 80 Deg F. at outlet of panel and shut down the pump if the temp is above 180. This seems to be a happy medium to stop the system from becoming a steam boiler.

I think the gurgling sound is from the drop, about 15 feet, from the top of the panel to the top of the drainback tank.