On/Off control of a Taco VR1816 in proportional pressure mode.
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This is in Northern Nevada. I have an older rental that has no heat in three areas of the house. The water heater I installed last year is a mod/con with two heat exchangers, one for DHW and the other for hydronic heat. I plan to add a high efficiency panel radiator to each area in a reverse loop and control them with TRV’s. Looks like the Taco VR1816 used in proportional pressure mode would be a great solution for a circulator. Problem I see is that on a warm winter afternoon its quite likely that all three TRV’s will close giving zero flow through the loop. I dont want to use a bypass valve which would result in the pump running 24/7.
So, without getting into much more expensive thermostats with lots of wiring (or doubly expensive WiFi thermostats), whats the best way to turn the pump off at zero flow AND back on again when one or more of the TRV’s starts to open?
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Replies
I think the intention is that the infinitely variable pump is left on - with no flow, power draw can be very low.
It’s fine to leave on in constant or proportional pressure mode. I have a similar Grundfos alpha pump with some panel rads and TRVs that never gets shutoff all winter. Ideally you should set the outdoor reset aggressively so that there is always some flow. Another option is to leave one rad without a TRV in a colder area and use the outdoor reset and flow adjustment to keep it from under/overheating.
Why not just their basic 007 model. Less than 3/4 amp. When it's off it's off.
The OP is trying to avoid having to add controls or bypass devices that would be necessary with 007. The VT is a great choice.
The VT pump will slow down as the TRVs close and will be quieter, use less energy and avoid the efficiency killing high return water temperatures that result from over pumping. Both the 007 and VT pumps can be turned off and on with a relay. The advantage of the VT is that you don’t actually need to turn it off simplifying the control strategy.
Another option is to put the thermostat in the coldest zone and don’t put a TRV on that rad. Use a relay to start and stop the pump when the thermostat calls.
I’m not sure how this pump compares to the Grundfos Alpha2, but the Alpha2 has some decent horsepower and uses under 30watts.
My Alpha2 loop for one zone is using 3 watts.
My Alpha2 is usually between 9 and 18watts. These smart pumps are amazing and pretty cheap too.