I'm heating a single building of about 3500 Sq Ft (will heat a second, smaller building planned for construction in about 5 years) with a Garn WHS2000, with Radiant in floor Pex. This is a vacation property for the moment, and won't be occupied full time for another 5 years. Here is my problem: I have a propane boiler in the building, which functions as a backup heat system. This propane system is providing backup heat about 50 to 80 % of the time, as I can't get the Garn fired as often as I'd like. Given the location of the heat exchanger, the propane boiler ends up back-feeding heat to the garn unit, via the flat plate Hx. If I turn off the circ pump from the Garn (Taco 007F5), I can see the propane boiler output temp jump rather fast, but with Circ on, it can burn for an hour without getting hot enough to hit its setpoint and stop firing. A lot of that heat is being backfed to the Garn. I can also see this by monitoring the temp of the supply and return, just before and just after the Hx. If my supply is at 100F, and the Propane boiler is firing and up to 130F, I'll see the return to the Garn going out at 115F. I need to keep circulating to prevent freezing, of course.
To a certain extent, this is good - it keeps the Garn from getting so cold that it freezes. But, it ends up costing me in Propane, as well as power to run the Taco 24/7. Is there such a thing as a variable speed or multi speed pump that can receive temp inputs and vary its pumping rate? What I'm picturing is a way to compare the supply temp and the return temp, and control pump speed based on the difference.
For example, if the supply and return temp are the same (or within a reasonable degree the same), then pump at low speed as the building isn't using any heat.
If the Supply is colder then the return, pump at a low speed as the propane system is firing and pumping heat out of the heated building and back into the Garn.
If the Supply is below 135F, then pump at low speed, as it is below the temp needed for heating the building.
If the Supply is above 135, and the return temp is 10 or more lower then supply, pump at high speed as the heated building is requiring and using heat from the Garn.
I know there are commercial solutions to this problem, but I'm struggling to understand them. Some just seem too complicated for my situation - I don't think I need to monitor outdoor air temp, or Propane boiler temp, or heated building temp, etc. The solution I descriped above would only require temp sensors located close to the Garn - one on supply and one on return, with no control wiring going to the heated building or outside the Garn shed. Are there existing commercial solutions that I've missed, or simple DIY options that I can implement? I'm comfortable changing pumps and can handle low voltage and residential voltage electrical systems, and think I could manage some modest control programing.
I'm anxious to hear suggestions or answer any follow up questions.
To a certain extent, this is good - it keeps the Garn from getting so cold that it freezes. But, it ends up costing me in Propane, as well as power to run the Taco 24/7. Is there such a thing as a variable speed or multi speed pump that can receive temp inputs and vary its pumping rate? What I'm picturing is a way to compare the supply temp and the return temp, and control pump speed based on the difference.
For example, if the supply and return temp are the same (or within a reasonable degree the same), then pump at low speed as the building isn't using any heat.
If the Supply is colder then the return, pump at a low speed as the propane system is firing and pumping heat out of the heated building and back into the Garn.
If the Supply is below 135F, then pump at low speed, as it is below the temp needed for heating the building.
If the Supply is above 135, and the return temp is 10 or more lower then supply, pump at high speed as the heated building is requiring and using heat from the Garn.
I know there are commercial solutions to this problem, but I'm struggling to understand them. Some just seem too complicated for my situation - I don't think I need to monitor outdoor air temp, or Propane boiler temp, or heated building temp, etc. The solution I descriped above would only require temp sensors located close to the Garn - one on supply and one on return, with no control wiring going to the heated building or outside the Garn shed. Are there existing commercial solutions that I've missed, or simple DIY options that I can implement? I'm comfortable changing pumps and can handle low voltage and residential voltage electrical systems, and think I could manage some modest control programing.
I'm anxious to hear suggestions or answer any follow up questions.
