I am coming to realize that my flat plate heat exchanger is undersized (5x12, 20 plate).  It works well most of the time, but when the setback program on our T-stats switch back to the warmer cycle, the HX gets hammered with a huge slug of cold water from the zones (all baseboard convectors).  The delta T on the GARN side of the HX goes from under 5 degrees to 25 or 30 degrees in minutes.  This situation often causes the oil furnace to cool off below its low set point, and the oil burner kicks on to supplement. 

 I know I need to upgrade to a larger HX, but I think a variable speed pump control would help alleviate some of the transfer shortfall.  I am using a 3-speed Grundfos UPS 26-99 for the secondary house loop off the GARN primary loop.  The 26-99 is set at medium speed.  I am using a Grundfos 3-speed UPS 43-44 for the primary pump, set on low.

Does anyone have any suggestions for a "simple" delta T based pump speed controller?  I'll be searching and posting over at the Hearth Boiler Room as well, so sorry for the cross posting for those that visit there as well.

Jim;

Have a look at a Tekmar 157.

Paul

Paul Duguay:

Jim;

 

Have a look at a Tekmar 157.

 

Paul

<chuckle>  Thanks Paul.  I had the Tekmar 157 literature in my hand as I read your post.  I just downloaded it.

jim,  i believe taco makes a setpoint series of 00 circulators, that will control pump speed based on a delta t , from 5 to 50deg, you adjust the desired delta t with a knob, also has a temp sensor for the return to garn

tom caldwell:

jim,  i believe taco makes a setpoint series of 00 circulators, that will control pump speed based on a delta t , from 5 to 50deg, you adjust the desired delta t with a knob, also has a temp sensor for the return to garn

 Tom - thanks.  Yes, I am/was aware of the TACO VS circs.  TACO is quite fond of them, too.  The price of one of those circs is more than the Grundfos 3 speed AND a Tekmar 157 combined.  I will experiment with the speeds some more on the Grundfos.  If ramping up the flow to high largelay addresses the cold start issues in the AM, then I know that the Tekmar will be a good solution.

When I re-do the zone plumbing next year I want to incorporate a VS pump that adjusts flow based on delta P.  With zone valves, a single speed TACO 007 has to act as a high head low flow pump when a single zone is open, and act like a low head high flow pump when all the zones are open.  Obviously it;s ideal performance is at neither end.

 I have used those in several applications and they work well.

Steve Ebels:

 I have used those in several applications and they work well.

Steve-are you referring to the Tekmar 157 or the TACO VS pumps?