pump placement & thermostatic mixing valve

Timbo

A job I am working on has a radiant slab with an electric boiler as the heat source. The installation is using a single grundfos pump on the boiler supply, there is also a manually adjustable shunt line ,3/4"ball valves, with a flow switch connecting supply and return headers which I assume is for dumping excess pump head. Boiler supply main has 2 high temp zones (convectors)with zone valves on the return and a 3 port thermostatic mixing valve serving a 7 loop manifold.There is no pump on the mixed outlet side of the mixing valve. What are the pro's & con's of this installation? 

EricAune

No flow through the manifold is a con...

You must pump away from a thermostatic mixing valve for it to do its thing.  If you are supplying the radiant manifold with mixed temperature fluid the circulator must be between the mixed port of the tempering valve and the supply of the manifold.



Check out these piping diagrams for installation guidelines.



http://www.taco-hvac.com/uploads/FileLibrary/5000MixValve%28PA07%29.pdf

zacmobile

depends

pumping from the valve to the manifold would be a plus for comfort by keeping the flow & temperature more constant in the radiant loops but depending on your piping scheme the way you have it may be essential for providing adequate flow through your boiler if its of the low mass kind, most electric boilers will specify (usually right on the boiler itself) a minimum flow rate.



this has some good info: http://www.heatlink.ca/en/system/files/Instructions/L6-63700-Compact-3-way-Mixing-Valve-Instructions-2007-05-08.pdf