Solar tank piping

TonyS

I have a solar tank that has lost its integral coil from acidity. I am going to install a external plate exchanger. I only have the cold water inlet and hot water outlet to tie my plate exchanger into the domestic side. What is the best way to pipe this without creating a bypass?

hot_rod

does the tank have a drain valve?

remove it and install a brass tee. Re-install the drain cock and use the additional port for the pump. remember the pump needs to be brass or stainless and have a check valve.



Pipe the HX with unions or Webstone purge valves so it can be easily de-limed.E



Don't forget the thermostatic micx valve on any solar tank



The HX pump runs when the solar pump runs.



Here is a concept drawing from Idronics # 3



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TonyS

Hot Rod

My hot and cold lines enter  directly into the tank. If I cut a tee into the cold line entering and tie back into my hot line at the top, What would stop my cold water from just bypassing the tank and feeding the hot line directly? A check valve wont work because it needs to be in the direction of flow? It would appear that I will lose the natural stratification in the tank because the pump on the exchanger, is that true and how important is that?

mark schofield

Grumman Sunstream picture

Tis is a picture from a Grumman Sunstream manual. When my solar storage tank started to leak, I bought an electric water heater from Lowes and plummed it as shown. My system has an external heat exchanger.

hot_rod

is it

a solar pre-heat tank, that feeds to another HW or indirect? Or does the solar tank have an electric back up element?



I prefer the dual tank, the first tank just for solar harvest, the next is the boost.



Yes you will breakup the stratification whenever the HX pump runs. So just run that when the solar pump is running. No need to mix the tank with the HX pump 24/7.



Wire both pumps to the solar controller, like the drawing shows. Watch the current draw, most solar controllers only switch 1 amp. If the solar pump and the HX pump together draw more than 1 amp, add a relay. Solar controllers are generally 120V output, so buy a relay, like an RIB with a 120V coil to wire directly to P-1 output.



You want the solar tank as cold as possible when the sun comes up to harvest the most energy, so not to "warm" that tank with a back up element, for example.



A tank with 4 ports is best for adding a external HX. You have H&C on top. The drain cock gives you a 3rd port. You must have a T&P port?



I've heard that some installers remove the T&P, add a tee then use a T&P with an extended sensor. You MUST have a T&P and it needs to have the sensor element reaching into the tank. I know Watts has extended probe T&P some indirect tanks ship with long probe T&P valves.



Or remove the anode rod, it probably needs a new one, then add a new anode nipple that is both a fill nipple and anode rod in one fitting. Now you have 4 ports.



If you tap into the cold yes you need a check above the tee in point. Cold can flow into the tank, but the HX pump cannot pump into the cold.



Of course you will also need a DHW thermal expansion tank if you put check valves on the tank.



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TonyS

It Is

a 80 gallon stainless tank that is a prefeed to a tankless navien. It had a internal, non replaceable copper exchanger inside that failed from acid water. I would have liked to cut the coil using an internal tube cutter but it will not fit because they are those straight running threads with a hose washer connector so I just plugged the exchanger. I do have a relief valve up top and a drain at the bottom but even with that configuration I dont see how I would be able to stop flow through the plate exchanger that would mix with my hot. 

TonyS

If I pull the water from

the top of the tank I can install the check valves to stop the bypass but this will send the hottest water in the tank to the exchanger first. How detrimental do you think this will be?

hot_rod

It will work fine

the outlet to the building will be regulated by the 3 way thermostatic also, so if the tank temperature varies, no big deal.



AO Smith had some tanks with external HX on the market a few years back. They displayed them at solar shows for a few years.



Or you can buy these PAW modules all pre-plumbed for turning blank storage tanks into solar tanks. Same concepts and components as we talked about. A bit more $$ if you want a nice custom module like this.



Heat Transfer Products also sell a module HX package for their Phoenix tank.



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hot_rod

Here is the AO Smith HX pack

looks like you can buy it without a tank.

TonyS

Thanks Hot Rod

I am going to pipe it just like the Promax.