Taco X-Pump Block questions / puzzles

bhowden

I have a Sanden hot water heat pump and am using a Taco X-Pump Block to siphon off about 4000 BTU/hr to a radiant floor loop. It is plumbed according to the guidelines supplied by Sanden and Taco and seems to work almost correctly. When I use the test function the variable speed pump spins up to 100% and then back down to 0 followed by the continuous pump running for 10 seconds followed by the head demand relay actuating. While the variable speed pump is spinning up the display shows the % sign and a bar graph indicating speed. When the continuous pump is running the display shows the correct icon for that pump as expected and described in the manual. When in actual operation and there is a call for heat the continuous pump icon is on but the variable speed icon is off. Both pumps seem to be vibrating a bit so I am assuming they are on. When the heat is first called for you can see the temperature start to climb towards the mix target temp for a few seconds and then falls back down. I am assuming this is the floor loop pump dumping a shot of cold water from the floor loop into the heat exchanger so expected behavior. After a minute or two the temperature climbs up but overshoots the target temperature by about 10 degrees and then stays there (10 degrees above target). My main concern is that I don't want to damage the floors so I was expecting the actual temperature (mix supply) to wander up and down a small amount from the target temperature. My two questions are:
1) Is it normal for the display to not show the variable speed pump speed (or even that it is running)
2) Is it normal for the supply mix to be so far above the target temperature?

Thanks in advance.

Brian

Rich_49

What temps are you using for the programming ? What temp is the Sanden fluid at ? Min odt should coincide with max swt and min swt should coincide with max odt . What Delta T do you have it programmed for , 10* or 20* ?

bhowden

Thanks for your response. As per Sanden's recommendations, the X-Pump is set for outdoor reset mode and boiler enable mode. I currently have the Sanden set point at 150F and the X-Pump sensor at mid Sanden tank reads about 135 after a heat pump cycle and the heat pump restarts when the mid point temperature falls to about 111F. The outdoor design temperature is set to 27F. This time of year the temperatures are typically high 30's to high 40's with an overnight dip to low to mid 30s. The Mix Design Temperature is set to 90F, the Mix Maximum Temperature is set to 95F, Mix Minimum Temperature is set to off, Boiler Protection Temperature is 130F and WWSD is set to 50F. Right now the Target temperature reads about 85F and the Supply Mix is 101F. I don't see anywhere to program delta T on the X-Pump.

Not trying to lead the conversation but is it possible that my heat demand is low enough that the X-Pump is not properly regulating it? In other words, could the variable speed pump be running so infrequently I am not seeing the indication on the LCD panel and even at this low level it is overshooting the target temp? I have noticed that when I go into test mode and the variable speed pump runs up to full speed over 10 seconds the supply temperature shoots way way up.

Thanks again for any thoughts.

Brian

Dave H_2

Brian,
Your suspicion is correct, the injection pump is barely moving in order to get to the target temperature. What that means is on the supply side (from the heat source) should be a balancing valve like a globe valve. You should be closing this valve in order to get the circulator to ramp up.

The best way to get this valve balanced properly;
1. It should be a design day temperature outside
2. Start closing the valve
3. The injection pump icon should get to 100% speed.

Now what you have is full capability of the circ to ramp up and down

bhowden

Perfect. Thank you very much for the help and suggestion on how to remedy it. I have ball valves on both the input and output of the X-Pump. I realize that Globe valves would be better for control but I can at least experiment and see how I do. Fortunately we don't get design temperatures very often but I get the idea. Am I correct in assuming it will be easier on the pump if I starve it a bit with choking the input instead of loading it down by closing the output or does this run the risk of starving the bearings?

As always, there is way more to every trade than meets the eye when you start out. I have found it very interesting but having a group like this with real hands on experience is invaluable.

Thanks again,
Brian

Dave H_2

I just re-read my post, I would like the balance valve on the return to the heat source, don't like to starve the pump as you were saying

bhowden

Thanks, will do.

Brian