Solar Heating Redivivus

I have had a thermosyphon system working quite well for 30 years without all the controls you have described. In your case they may be neccessary due to gravity or thermosiphon restrictions. My best advice is to put the output from your collector to the midpoint of your hot water tank. Draw the collector feed from the bottom. The top of the tank is your output. This all works very well on gravity or thermosiphon if your hot water tank is above the collector. If not, then you will need temp. differential sensors and controls running circ. pumps.

Redraw and see how many 'controls' you can eliminate. 'KISS' works better here.

The collector is on the roof, 10 ft above the ground. The water heater tank that will collect and store the hot water is on the ground level, being some 6 ft tall. The water heater can, also, get energy from burning propane on its bottom (a regular gas water heater). The whole system is closed, there is no loss of water. I intend to use it for warming two bedrooms (or at least to reduce the amount of paid energy for that purpose).

What were the maintenance problems with your system? In 30 years, I think, you have had some.

Principle remark:

- in a heating element the way you though it you obtain the highest transfer since the flows are in conter sens but there is the risk of air pockets on top an los of heat transfer surface. So better put entry at bottom and outlet at top air will go with the flow.

- if heated water entry the top of the reservoir there is less mixing, risk of gradient over the height.

I was thinking that the "cold" water for feeding the heat collector on the roof will be taken from the bottom of the storage tank (that might be use for heating water in "dark" days. That is the heating phase. When water in tank reaches a certain temperature, the flow is reversed, and the "hot" water is taken from the top, brought to room radiators and recirculated back to the bottom of the tank. You are right, I have to have the return from the collector, the "hot" water, somewhere in the middle, to favorites mixing. In fact, Tippycanoe told me the same.

I see now! I need three "ports" on the top of my tank: one with a deep pipe to the bottom of the tank which is the "cold water" suction; one with a pipe to the middle of the tank with "hot" water return from the collector; one from the top of the tank for the "hot" water for room radiators.

You mention the risk of air pockets on top. Is it on top of the collector or the tank? My system is a closed one, I circulate water only, for heating. I do not intend to use for washing dishes.

Perhaps I should explain my hookup, and you can see how this works. The cold water input at the top of my electric water heater is plugged off. Supply and collector feed comes into the drain at the base, where the boiler drain has been replaced with a tee, and drain at the end. The return from the collector enters at about 2/3 of the height of the tank, where another tee allows the temp/pressure safety valve to be installed in it's original location. You may wish to remove the down tube from the cold water inlet and put your safety valve there. Hot water comes off the top. My collector is a series of zigzag 3/4" x 6" nipples, El's and street El's inside a wood stove. Replacing the original galvanized collector with silver soldered red brass, and a new water heater have been the only upgrades. Drain the tank every few years to remove sediments. An air purge can be added to the top.

I recommend the generous use of unions and valves where ever you can. You may also want to use a heat exchanger/antifreeze system depending on your location. I use a closed loop blower driven hot air to thermal mass system for home heating. I think this is the cheapest, most effective way to use solar radiation. The backup heat kicks in about dusk (I light a fire in the wood stove). A 130 watt PV array/battery system drives it all, and supplies emergency lighting as well.

Do you use 3/4 copper tubing inside the stove? The soldering is with silver, you say. Are there many soldered joints exposed to flame? (I understand, they have water inside). How do they behave, in time, to the flame heat?

The safety valve in my tank is above the 2/3 line so I think that I will use a shorter pipe on the "cold" port on top of the tank. I will use the drain on the bottom. although for now, I cannot tell the effect of flame heating on the bottom of the tank. If I find an unused (plugged) opening on to of the tank I think I am going to use it. Right now, the top is covered with solidified foam.

You should have two ports on top of the tank. The cold inlet has an easily removeable sleeve, so that your safety valve can be installed right there. No short pipe needed.

The red brass I used was threaded pipe, threaded fittings. The silver solder was used because the joints would leak after a couple seasons of heat/cool cycling.

Hi , I have to say that solenoid valves are no suited for this work .

As it need a high diferential pressure to be operate.

And in such circuit there is a small diferential pressure each side of the valves

Also it load a high head pressure to the circuit.

You shall use FANCOIL motorized valves .

I have a box fill with solenoid valves that I have to take off from work site.

Hi devitg

I am a bit confused, so I want to make sure that I understand.

I have the 1/2 HP electric pump that creates quite a pressure in the system. You say that due to this pressure I cannot open or close the solenoid valves? Or you thought that there is no pump and the low pressure would prevent the valves from working?

Anyways, if the high pressure could be a problem, I just turn the valves on or off before starting the pump. My PLC has plenty of timers, so that would be not a problem

Hi Gabriel,

Thank you for your detailed explanation. That may me think that my hydraulic circuit might not be as simple as I thought.

My valves are 24Vdc, normal closed, Parker. The specs data sheet tells that the minimum pressure is 0psi and maximum 250psi.

From the click that I hear when I energize the solenoid, and blowing air into it, I thought that the valve can open even in a differential pressure and can close due to the spring inside. I have 20 such valves so, I will try to use them. If I will have any problems, I will dare to ask your help.

Thanks,

Nicholas

Please give the parker´s model , Maybe it is a solution for me too.

In fact they are made by Skinner Electric Valves which has been taken over by Parker.

Valve number: C2DA1261 (code: DA8)

I don't see a room thermostat in your layout.

Perhapse you could step through your basic logic for the controls.

There are several thermocouple sensors with 4-20 mA transmitters (own production) that monitor water temperature in the water heater tank (three levels), two in the solar collector and two in the bedroom.

The signals from those sensors is analysed by my PLC program and the pump is activated, pushing water from collector to tank or from tank to bedrooms.

The collector area is some 20 sq. ft. so the maximum energy transferred from sun is barely enough to rise the temperature of the 50 gallon of water in the tank.

This is why, I bought a 50 gallon gas water heater, to supplement the necessary energy in case that solar is not enough. Also, it will be a cost analysis. What I am sure of is that I will use the system and it will lower my bills (with a break even for the installation cost within two or three years).