HX Output Tempering

[Hunderliggur]

I want to limit the output of my heat exchanger to 135F to use for radiant heat and domestic hot water. I was orginally considering a tempering valve but they have some limits (cost for 1 1/4" valve, "cold" input limit 80F, etc.). What I want to do is run the radiant return through the in tank heat exhanger if the tank temp is greated than the return temp, then limit the heated supply temp to 135F by mixing with some of the return flow. This is kind of like modulating the boiler return temp except I want to limit a maximum temperature. I am using 1 1/4 to limit head loss in the piping for the 3 zone and DHW (max flow is 9GPM for the three heating zones). Does someone know of a pump control and controlable circulator that could do this? In the left hand side of the drawing in the circulator based control logic (if tank is colder, no pumping and water will take path of least resistance bypassing the heat exchanger). Pump speed is decreased if the supply temp is greater than 135F allow mixing with the return flow (<120F). On the right is a Taco EBV approach using a tempering valve (if I can find one that will take up to 120F cold water input). Thanks for your help.

 

[Hunderliggur]

Has anyone used the Taco 00-VS series in their system? It looks like it can do the trick (and they have some excelent installation sizing information). http://www.taco-hvac.com/uploads/FileLibrary/00-VS(PA05).pdf

 

[ewdudley]

I want to limit the output of my heat exchanger to 135F to use for radiant heat and domestic hot water. I was orginally considering a tempering valve but they have some limits (cost for 1 1/4" valve, "cold" input limit 80F, etc.). What I want to do is run the radiant return through the in tank heat exhanger if the tank temp is greated than the return temp, then limit the heated supply temp to 135F by mixing with some of the return flow. This is kind of like modulating the boiler return temp except I want to limit a maximum temperature. I am using 1 1/4 to limit head loss in the piping for the 3 zone and DHW (max flow is 9GPM for the three heating zones). Does someone know of a pump control and controlable circulator that could do this? In the left hand side of the drawing in the circulator based control logic (if tank is colder, no pumping and water will take path of least resistance bypassing the heat exchanger). Pump speed is decreased if the supply temp is greater than 135F allow mixing with the return flow (<120F). On the right is a Taco EBV approach using a tempering valve (if I can find one that will take up to 120F cold water input). Thanks for your help.

It looks like you need to inject heat from the tank HX into your load loop either with closely spaced tees or using a hydraulic separator.

You could use a differential thermostat to decide if the tank temperature was hotter than the return temperature, but perhaps more to the point might be a simple aquastat that would disable the heat-from-storage-injection-loop when the storage temperature was below some minimum.

The Taco VS type pump would be able to modulate the rate of heat injection nicely, just add a sensor downstream of the injection point, tell the VS what your setpoint is, and enable the VS any time there's a call for heat in the load loop.

Also check out some of the Tekmar controls, they've got this stuff pretty well figured out.

Here's an article that discusses a lot of what you're coping with:

smartgreenbuild.com/blog/download/582/