Pump continuously or cycle on / off

ecky

Just wondering if the current line of thought favours running variable speed pumps continuously - or to cycle pumps on or off as needed? I have a GARN unit (boiler) located outside about 50' from the house. I am trying to determine whether running a VS pump continuously would use less electricity then having one go on or off when load demands occur. The unit is to provide heat for 2 stories of radiant floor, and DHW. The other concern that comes to mind is that pumping hot water constantly would lead to more heat loss underground since the temp differential between the water in the underground pipes (insulated) and the ground would remain higher. The house is very efficient. I am located at the 45th parallel. Any thoughts?

Brad White

Some thoughts

If the outdoor boiler is open as I suspect it is, it will not have glycol so has to be kept moving to avoid freezing. That might answer your question right there, at least for your boiler-side.



For the interior spaces/circuits, that is open to analysis.  (I am assuming here that you have a plate heat exchanger or other means of primary/secondary piping that requires a circulator for the interior spaces.)



If the spaces are left vacant for extended hours per day then cycling may make sense. Your good building enclosure and access to higher temperatures say to me that your recovery times may be very short, not a lot of waiting for comfort.



If the spaces are occupied but with limited excursions, constant flow is hard to beat in terms of comfort. With a good VS circulator, the cost will be minimal. If you are in PQ with good electric rates (does ON have good electric rates too?), this may not be a strong issue.

NRT_Rob

best of both

run the trench pump as a variable speed injection pump, but work some electric hoodoo voodoo to ensure minimum circulation when there is no heat demand and/or when the trench is at too low of a temperature.



If you can't do that, use an ECM pump. it will pay for itself in a season or two unless your electricity is dirt cheap.

ecky

Some comments on some thoughts

Sorry Brad - I was negligent in mentioning that the unit is open but is very well insulated. 5000 L (1500 US gal) of well insulated water is not going to freeze for quite a long time. Sorry I didn't provide that info.



I was going to have a plate collector feed off the primary circuit to the DHW. I was then going to have one circulating pump run the 2 secondary loops (radiant floors - upstairs and downstairs). When there is a call for heat from the thermostat or DHW - the primary loop would be activated.



The house would be vacant 5 days a week while we are at work - and the odd weekend. Recovery would depend upon how cool I let it get amongst other factors of course. It is a very slow recovery now but that is because the heating system (the temporary one I am trying to replace) is grossly undersized. Based on your statements - this seems to suggest that I go with cycling as opposed to a VS pump. Would you concur now that I have provided additional info? This raises the question about how cool one should let the house get in winter over an eight to ten hour period? Allow the house to drop a couple of degrees and maintain - or let it drop to whatever and have it set to get back to temp just before we get home. I appreciate your thoughts and input.

ecky

Re: Best of both

Hi NRT_Rob: Thanks for your input. However, I am confused ( not surprise there). Can you not have a VS ECM so in fact they could be one in the same? Hydro rates here run 6 to 8 cents per KWhr.

NRT_Rob

no

not yet anyway. I'm not aware of any ECM pumps that can modulate based on an external demand signal in the residential market.



if you were doing commercial grade stuff you could, but you probably don't want to buy a $1000 pump to make that happen...

ecky

No to ECM VS

What took you so long to reply? ;^) Much appreciated Rob. I had found one but I will have to go back and have a look - it may very well be a commercial model. Thanks for your input.

ecky

No to ECM VS

What took you so long to reply? ;^) Much appreciated Rob. I had found one but I will have to go back and have a look - it may very well be a commercial model. Thanks for your input.

Brad White

The Wilo Stratos

can accept an external analog signal. This is not their Stratos Eco but it is at the upper end of what I would call the residential line.



The Grunfos Alpha and Magna may also have this capability but I am not sure.



The Taco VS series of 00 circulators have been out for years now and also accept an externally generated analog signal. Make sure you select the correct application when you order, these are not interchangeable..



These  Taco VS series are not ECM motor circulators but PSC (permanent split capacitor) motors, so the cube-root savings of an ECM motor is not there, but it is more or less proportional to the load, not even a square root function but they do save energy. Given your relatively low electric rates (however impermanent they may be), the Taco VS series might make sense for you.



My first advice though is to have a good pump selection no matter what pump you use. Do not trade away what is an ideal pump selection for one with possible higher efficiency. Know your flow and head to as high a degree of certainty as you can, then find the best pump for that duty.