Piping design when two parallel storage tanks used to preheat water.

[ChrisMegyes]

thanks

thanks forr the info

[LAWindsurfer]

parallel reverse not key problem

parallel reverse???

Ideally, parallel storage tanks should be configured such that there is equal flow between the two parallel tanks. My tanks may not be configured for nearly equal flow, but that was not the main problem. The system was originally configured to use heat exchangers built into the storage tanks to transfer the heat from the collector circulation line to the storage tanks. They proved to be very poor an heat transfer. After an external heat exchange was installed, there was a very dramatic increase in the heat transferred from the collector circulation line to the storage tanks. The system has been working just fine and gas use during the summer months has dropped by a factor of two.

[svi]

Diagram attached

What is meant by "parallel reverse?"

Effectiveness of solar hot water heating is being judged by comparing cu.ft. of gas consumption (with correction for BTU content) for three years prior to installation with gas consumption over most recent year.

parallel reverse???

[svi]

Attached chart shows that water use and gas consumption does not appear correlated. Solar installed December 2010. Unknown if gas consumption goes up in the winter because people take hotter showers or because of increased losses in (insulated) hot water circulation line. Hot water circulation line is heated by gas since it circulates the water in the gas fired water tank. Hot water circulation pump is controlled by sensor on return line except during morning and evening "rush" hours. Pump runs when water at return point drops below 110 oF and turns on when temp rises above 112 oF.

It seems to me that the reverse parallel connection would only make a big difference if the plumbing between the tanks obstructed the solar water flow by an amount comparable to the obstruction represented by the heat exchanger coils.

I'm in the process of instrumenting the configuration with max/min thermometers to see if all of the pre-heated water is used up during the night.

the piping connection should always achieve equal pressure for each tank

[fishpickler]

just replying

[hlukeh]

Alright, well I'll start with the 3-way valve setup.

I'll just have to figure out how to get a second 3-way valve connected to the controller to dump the excess heat into the geothermal ground loop once the two tanks are hot... Actually, the geothermal heat exchanger loop could just be in series with the high temperature heat dump which is a separate function on the controller.

LucMan, the manual you attached is quite similar to mine! It must be the same manufacturer controller.

Now that I've gotten a few posts on this thread, I probably shouldn't have hijacked it

SR1188 Manual.pdf

[Mike90250]

Less complicated. Figure out what can fail, and how you work around it. What about frost protection for the solar ?
Solar is good for preheating the water, and if you get it 80% of the way to HOT, then the electric takes over and finishes it. Heating 2 tanks, the electric (I assume the 2nd heater is electric ??) will try to keep BOTH of them hot, beyond the range of the solar assist.

[hlukeh]

I like the idea of the three way valve and heating one tank, then the other, but I'm not sure why you guys suggest not heating both tanks from the solar?

Luke

[LucMan]

First lower the thermostats on your electric strips to 110 degrees or lower if possible.
By using a 3 way valve I would heat 1 tank at a time (primary tank) to a set temperature with the solar ( 120 -130 degrees?). Then the 3 way valve would switch to the next tank heating that tanks water. Turn off the circulation between the 2 tanks unless you have sufficient capacity with your heat pump to heat the water to the desired temperature. Then a thermostat could bring on the pump to circulate excessively hot water between the 2 tanks
refer to page 20 in the attachment for the 3 way valve.
The 3 way valve would be piped into the outlet of the HX.

[russ]

I agree - one tank with two heat exchanger coils would serve the purpose nicely

One coil for the solar and one for the heat pump

[Mike90250]

I think I'd only use the solar in the preheat tank, and not circulate between both tanks.

[hlukeh]

Best way to hook up two hot water tanks with a solar pre-heat tank

I'm trying to figure out the best way to hook up two hot water tanks with a solar pre-heat tank and a main tank that the domestic hot water is drawing off. My setup currently has a geothermal pre-heat on a single tank, which is a poor setup because I've been monitoring the heat pump and water heater run times and the water heater runs just as often whether the heat pump is running or not.

I wanted to look at the attachments in the posts in this thread but since my post count it 0, it won't let me.

I came up with a design for two tanks that I thought I'd go with, and it's attached, but after I look at what you guys have all suggested, maybe I'll change it.

The only designs I have found so far are of the solar energy heating a pre-heat tank, and then the main tank drawing from that. I don't like that design because as the heat is lost from the main tank, the elements will turn on even if the pre-heat tank is way hotter.

water heater setup.JPG

Water heater design.pdf

Luke

[LAWindsurfer]

summer and winter gas variation & plumbing path lengths

Good point about inlet water temperature being colder in winter. I had not thought of that.

As for imbalance between tanks on left and right, sketch did not attempt to communicate plumbing path lengths. I was only seeking to show connections and flow directions.

Thanks for suggestions and comments.

[Naptown]

Attached chart shows that water use and gas consumption does not appear correlated. Solar installed December 2010. Unknown if gas consumption goes up in the winter because people take hotter showers or because of increased losses in (insulated) hot water circulation line. Hot water circulation line is heated by gas since it circulates the water in the gas fired water tank. Hot water circulation pump is controlled by sensor on return line except during morning and evening "rush" hours. Pump runs when water at return point drops below 110 oF and turns on when temp rises above 112 oF.

It seems to me that the reverse parallel connection would only make a big difference if the plumbing between the tanks obstructed the solar water flow by an amount comparable to the obstruction represented by the heat exchanger coils.

I'm in the process of instrumenting the configuration with max/min thermometers to see if all of the pre-heated water is used up during the night.

remember that the flow will take the path least resistance. In the diagram you sent the path of least resistance for the solar loop is through the left solar tank and the water loop is the tank on the right.
You have an unbalanced situation on both the solar and water sides.
By your chart it also appears that water use in the building increased about the same time the solar went in.
If you really want to instrument put a revenue grade BTU meter on each solar tank. That will bring the imbalance to light quickly.
As far as using more gas in the winter yes people will tend to take longer hotter showers then. But also remember that during the winter the outside temps are cooler than in summer. Water is stored overhead in tanks so the incoming water temp will be higher during the summer than in winter.

[LAWindsurfer]

Impact of solar on gas consumption took water use into account.

Attached chart shows that water use and gas consumption does not appear correlated. SOLAR installed in December 2010. Unknown if gas consumption goes up in the winter because people take hotter showers or because of increased losses in (insulated) hot water circulation line. Hot water circulation line is heated by gas since it circulates the water in the gas fired water tank. Hot water circulation pump is controlled by sensor on return line except during morning and evening "rush" hours. Pump runs when water at return point drops below 110 oF and turns on when temp rises above 112 oF.

It seems to me that the reverse parallel connection would only make a big difference if the plumbing between the tanks obstructed the solar water flow by an amount comparable to the obstruction represented by the heat exchanger coils.

I'm in the process of instrumenting the configuration with max/min thermometers to see if all of the pre-heated water is used up during the night.