Newbie to solar water heating need advice.

Silver88

New Member
Okay, so I'm trying to build a heating system for the ground floor (to start) of a small garage. I have acquired two solar evacuated tube water heaters 30 tubes each with heat exchanger. I have a circulating pump and thermostat. Now I'm about to pick up a cast iron radiator or two. The garage is insulated and has concrete block wall for two walls and a concrete floor (hoping the thermal mass of the radiators and concrete will help retain heat after sundown.

I'm hoping to do what I believe is what they call a "closed loop" system if I understand correctly...in which the water/glycol mix will circulate through the system/radiator and hopefully heat up the space enough to keep it at least above freezing in the winter. I live in Pennsylvania for reference.

The issue I'm having is that after the sun goes down I no longer want the water to circulate through the radiators or inside pipes sucking heat away. I'd prefer to keep it circulating occasionally (if at all?) on an isolated outside loop after sundown - which this outside loop would also be used to dump excess heat in the summer or heat potable or non potable grey water (depending on setup) via a copper coil on the closed loop system submerged or wrapped around in an insulated tub or something like that.

If I have my circulator pump on a thermostat to run when the temp gets to the setpoint for the inside zone or loop - how do I make it switch zones automatically at sundown?

I should also add for reference this is an off grid solar powered garage so any power must come from my 24v battery bank therefore I'd like to keep power usage to a minimum. There is no access to running water (I have a rainwater collection system with 275 gallon totes) I also am not there everyday to manually switch the flow from one zone to another when the sun goes down.

Is this even possible? If I use the glycol mix do I have to circulate the water to keep it from freezing if, it's in the outside loop, if not it'd save my batteries.

It seems most people who install these solar water heaters are using them for domestic water heating and have storage tanks, and running water that fills automatically etc. I simply want to heat a space with a radiator - and in summer use it to heat water for various uses with the dumped heat.

I've searched and read and only found bits and pieces and so far I'm still struggling to figure it out. I wouldn't have made a new thread if I didn't think the circumstance/setup was unique needed explanation to understand what I'm trying to do, so hopefully this is in the right spot.

Thank you all in advance, I truly would appreciate any help/suggestions in an get.
 

drunkenmugsy

New Member
I am looking to do something similar with a wood kiln. I will have a solar hot water loop. I am planning on using software called Home Assistant. It is used for home automation. You can do just about anything with it and an add-on called node-red. Check it out it is free. You can even run it on a RaspberryPi = low power. I will have a RasPi situated with my solar equipment to control relays and other stuff like a circulation pump and fans based on input from temp/humidity sensors. It might be a little overkill but you can do it with some hardware and some automated valves. Home automation is not cheap though. That will be my limiting factor. I am not sure I want to dump hundreds of dollars just to make a valve open and close. I will be using it to control fans, the circulation pump and other equipment for sure though.
 

Silver88

New Member
I am looking to do something similar with a wood kiln. I will have a solar hot water loop. I am planning on using software called Home Assistant. It is used for home automation. You can do just about anything with it and an add-on called node-red. Check it out it is free. You can even run it on a RaspberryPi = low power. I will have a RasPi situated with my solar equipment to control relays and other stuff like a circulation pump and fans based on input from temp/humidity sensors. It might be a little overkill but you can do it with some hardware and some automated valves. Home automation is not cheap though. That will be my limiting factor. I am not sure I want to dump hundreds of dollars just to make a valve open and close. I will be using it to control fans, the circulation pump and other equipment for sure though.

Interesting, I didn't think about that avenue tbh. I do have an arduino it's no raspberry pi, but it's something to look I to and is low power. I'll definitely look into it. Thanks for the idea!
 

Hedges

I See Electromagnetic Fields!
If your glycol mixture won't freeze at your coldest temperature, then you don't need to circulate water to prevent freezing.
If you use potable water then you will have to.

I think heat transfer to slab will be slow. Ideally you would place tubes before pouring concrete, but you're stuck with what you've got.

You will get the most solar heat when you need heat the least. Do some math on what size and temperature water heater would hold enough to heat the home in the morning or whenever desired.

You're likely to need an expansion tank.
 

jhx

Offgrid living
Did you build your system yet ? ( i can see its back from December?
I´m planning to do something similar.
But with water pipes under the floor.
In your case, I would add alot of clay/cob mix around theIron radiators
A circulate pump on the load out from the CC with a on/off switch for summer period off. Then your water
only circulates when the sun is shining.
Else use a timer.
And you will have a simple automated system.

Glycol freezing problem. No, if you follow the ratio water-glycol mix your system will be safe :)
 

jhx

Offgrid living
Did you build your system yet ? ( i can see its back from December?
I´m planning to do something similar.
But with water pipes under the floor.
In your case, I would add alot of clay/cob mix around theIron radiators
A circulate pump on the load out from the CC with a on/off switch for summer period off. Then your water
only circulates when the sun is shining.
Else use a timer.
And you will have a simple automated system.

Glycol freezing problem. No, if you follow the ratio water-glycol mix your system will be safe :)
Remember to add a overboil protection on top of your system
 

SolarPrep

Solar Enthusiast
Silver88: Look up "solar hot water controller". There are many units made for controlling exactly what you want to do. They range from about $150 up to who knows how much. Most of them are made in China, regardless of the name on them. If you google a solar hot water panel company, they also sell those units, but for more money.

Just a couple tips: insulate as much as you can. Nothing can be done about your slab now, but the rest might be do-able. I prefer using rigid insulation board over any type of fiberglass.

Cast iron radiators are great. Make sure you flush them out before hooking up. On a system like that, you should always have a high temp filter in line, to filter out any iron particles, etc. If you are planning on only using the heat from the panels, think about a storage tank. You also need to bleed air from the system, so an air eliminator is nice, and often they call for an expansion tank. All of this can be found on line with lots of drawings.

Good luck!
 

KeithBriggs

New Member
A few thoughts. You can staple pex down on the floor and poor self leveling over it and wala - your floor is the radiator and its not even 1.5" thick. 2. sun-earth makes a decent simple usable controller with two sensors. You can also put an inline timer (old fashioned dip switches on 10 or 15 minute increments to turn on/off your circ pump. I still much prefer the smart controller. You should have an expansion tank in (every) closed system. I mount mine upside down (theads down) with a shut off for easy replacement. precharge it to the pressure of your system where its being installed. Also need a tps on the roof. I agree: Insulate and and wrap the foam with orbits pipe wrap tape on the roof o/w the foam will get brittle and disintegrate.
 

SolarPrep

Solar Enthusiast
Silver88: just reread this thread. You cannot have a closed system, and have it in a tub wrapped with insulation. It must be sealed, and pressurized to use glycol. If you combine with other water heating, the glycol should be on its own loop, and run through a water to water heat exchanger with its own separate pump.

Do yourself a BIG favor and Google "drainback" systems. Much simpler, if you live in snow country. When sun is out, pump comes on, pumps water or glycol mix up through units, and it trickles back down to a tank. The system isn't sealed. At night, when the controller senses the cold/freezing temps, it turns off the pump, and water drains back by gravity. It must be designed to reliably do this. This is the approach I prefer.

If you have evacuated tubes, you might not be able to use this approach at all, if they are not designed to gravity flow. Most have the inlets that deal into the collector heads, and those are a closed system. You still need all the other components mentioned before. The key is bulk water storage. The bigger, the better. You can build your own tanks if you are handy. A couple hundred gallons, when heated up, can give off a lot of BTU when slowly pumped at night. Maybe with a battery back-up system?
 
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