solar with radiant-control strategy

jhowe88

Hello to all. I'm a first time user on Heating Help and a wholesaler salesman that calls on Dan Foley from Foley Mechanical. I constantly ask Dan for advice on certain jobs to do the right thing. I'm trying to get more knowledgable in hydronics and I figure that I would come to ask the other experts from Heating Help than bothering Dan all of the time.

I have a job working with a contractor that has radiant tied in with solar as the primary heat source and a Prestige Solo 60 as the backup. A dedicated solar contractor did the solar only. The solar contractor has no part in the final control setup.

The control strategy that has been proposed is to have the solar space heating storage tank provide the primary heating(storage tank set at max 105deg) then kickover to the Prestige Solo 60 boiler once the solar can't keep up. The solar controller is a Sun Earth model TR0301 and would like to use in conjunction with a Triangle Tube Optima S2S(Two Stage set point controller) which will stage the complete system with the Solo60. Specs provided of each below.

I'm asking for any advice with the control strategy that I have provided that these controls will do what we are looking for. This is the first time I have been involved with solar and the mechanical doesn't have much experience. Any advice would be greatly appreciated.

NRT_Rob

fun stuff

First, I would say that it's unlikely solar will be able to provide most of the load in any building most of the time. Sounds like a small load, so maybe, but it seems unlikely.



A bit depends on what kind of water temperatures the radiant system needs. But my favorite method is to send the radiant return (the coldest water in the system) through a top mounted coil in a solar tank (hottest part of the tank) using a differential control to determine when transfer is ok and a 3-way zone valve to divert flow instead of adding a pump.



in this way, you can use solar whenever it is hotter than the radiant return instead of it having to be high enough to satisfy the demand. keeps the solar tank cooler and more efficient at collection as well.



However... you have to have a heat demand for that to work, and a lot of times when your solar collection is best (warmer sunny day) your heat demands are least frequent. You can also "overcharge" the house, if the clients want to maximize solar. that requires funky piping or a dedicated emitter like a radiator. tank is hotter than room, dump, up to a max temperature set on a dedicated thermostat or setpoint control for the purpose. really good if you have slab floors you can charge up, but nice anyway... get those BTUs out of the tank as much as possible so you can keep collecting.



fun stuff!

Martin Romero

Control Setup

Rob,



How is your control set up to compare the temperature of the radiant return and the temperature at the top of the tank?  Do you use one controller with multiple relays?





Interested,



Martín Romero

NRT_Rob

nothing special

just a standard differential control like a tekmar 156. If A > B, flip the valve, if not, don't. there is a "differential band' in there of course but it's actually pretty simple.

jhowe77

thanks

I appreciate the comments and advice NRT.Rob. I haven't used Heating Help that much, I will now. Thanks again!

Bob Gagnon plumbing and heating

Use a separate radiant system

If you use a separate supplemental radiant panel for use with just the solar you will harvest a LOT more energy and use your solar panels on every sunny day, harvesting the maximum amount of solar hot water. You simply get what ever low temperature water you can get out of your collectors in the winter, and run this panel at the same time as your other heating system, when you have to. This also keeps the piping and controls simple, inexpensive and with less maintenance.



Thanks, Bob Gagnon

atomic

beware

Many solar/radiant jobs I've seen rely on a boiler for back-up, of course. But when there's no solar heat in the storage tank, the returning water from the radiant system heats the storage tank as well. Make sure to install controls to bypass the tank when the return water is hotter than the tank, or your gas boiler will heat the storage tank, wasting energy. Use a snap switch or differential controller operating a NO and a NC automatic valve at the same time on a tank by-pass.

ChrisB

More Questions

I am a homeowner and just discovered this thread.  I have a four-panel solar thermal system that is tied in to my domestic hot water and hydronic heating system.  The heating system is a combination of old radiators and pex in a slab and under the ground floor.  The boiler is a Triangle Tube Prestige 110.



My installer has the return water from the heating system return through the 125-gallon solar tank with no valve.  As a result, the boiler heats the tank to some extent.  I am not very concerned about losing energy because the tank is well insulated and at some point I recover the energy by using the domestic hot water.  However, I am concerned that the setup results in less energy being harvested from the panels since the tank is being heated by the solar and the boiler.  Is this a real concern?



Also, I have asked the installer to install Honeywell TH6000 series 2 stage thermostats so that the solar is used to heat when there is energy in the tank and the boiler kicks in only when the solar cannot maintain temperature.  The thermostats have pre-defined controls for when the stage 2 boiler heats kicks in, and it is not possible to adjust the point at which stage 2 takes over.



I am also considering installing an Optima 2S2. Would this controller help or should I make other modifications to the system?  I appreciate any advice that you guys may provide.

ChrisB

More Questions

I am a homeowner and just discovered this thread.  I have a four-panel solar thermal system that is tied in to my domestic hot water and hydronic heating system.  The heating system is a combination of old radiators and pex in a slab and under the ground floor.  The boiler is a Triangle Tube Prestige 110.



My installer has the return water from the heating system return through the 125-gallon solar tank with no valve.  As a result, the boiler heats the tank to some extent.  I am not very concerned about losing energy because the tank is well insulated and at some point I recover the energy by using the domestic hot water.  However, I am concerned that the setup results in less energy being harvested from the panels since the tank is being heated by the solar and the boiler.  Is this a real concern?



Also, I have asked the installer to install Honeywell TH6000 series 2 stage thermostats so that the solar is used to heat when there is energy in the tank and the boiler kicks in only when the solar cannot maintain temperature.  The thermostats have pre-defined controls for when the stage 2 boiler heats kicks in, and it is not possible to adjust the point at which stage 2 takes over.



I am also considering installing an Optima 2S2. Would this controller help or should I make other modifications to the system?  I appreciate any advice that you guys may provide.

hot_rod

a number of ways to control

combi solar systems. As always it depends on how much you want to invest and how much capacity you want to store. A dual coil tank is a simple method, then feed to the back up DHW source. With multiple tanks you can best prioritize to maximize the collector performance.



When the solar gain is low it is wise to pre-heat DHW even if you cannot reach temperatures high enough to cover heating loads.



Think low, low distribution temperature emitters to drive the highest collector efficiency.



A cool collector= a happy collector is how Jim Huggins tech director of the SRCC explains it



hr

ChrisB

Thanks

Thanks for the feedback.