Control Question - Boiler and pump on demand only

cgw

<span style="font-size:12pt">A fraternity building (which could be a large house or a small dorm) with hot water heat. My situation is that the heat is supplied by a steam-to-water heat exchanger using campus steam but a low volume condensing boiler would be similar.</span>

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<span style="font-size:12pt">Is there a building size below which starting the pump and opening the steam valve (running the boiler) only on demand from one of the zones makes sense?</span>

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<span style="font-size:12pt">For example a house with four zone valves and themostats. If one or more called for heat, the boiler and pump would be enabled. Otherwise they would be off.</span>

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<span style="font-size:12pt">The other alternative is that the pump runs and water is heated to set point 24/7 during the heating season (presumably with outdoor air temp reset).</span>

SWEI

clarifications

I'm not really clear what you're trying to do here.



Is campus steam available 24 x 7 x 365?

cgw

smaller buildings

I am trying to avoid the pump being on all the time in smaller buildings.

SWEI

still not really clear

What the setup is.  Again, is campus steam always available?  One HW circulator pump per remote building?  Assuming so, I'd want to run an ORC to modulate water temp in each building plus a WWSD to shut off the pump when the temp got above that point.

Zman

Makes sense

The question of the control of the circulator during the heating season is a little tricky. How old is the system? How is it set up? Is it an older system that likely to start leaking if it exposed to big temp changes (expansion and contraction)? Some indicators might be; does the system leak when cold? Is the system noisy when going from cold to hot? Is this a converted gravity system with huge pipe sizes?



Your idea of warm weather shutdown and outdoor reset are right on. There are certainly some energy savings to be had.You want to have some comfort level that there will not be unintended side effects of the changes.



I think if you post a little more info and maybe some pictures you will get the answers you need.

cgw

small bldgs

My question is hypothetical.

I would think for a small house, the pump and boiler would run on demand. For a larger commercial building the pump would run continuously and the water temperature would be maintained.

Is this a good assumption so far? (I am not usually involved in residential hot water projects)

Assuming the above, where is the cut off between the two?

If you had a 5000 square foot house with several control valves, would you leave the main pump running?

SWEI

size doesn't matter

ODR makes just as much sense for a 200 sq ft outbuilding with one zone as it does for a 200,000 sq ft hotel that has 400 zones.  If the boiler can modulate, it should.  If not, then the ODR would control a mixing valve and the boiler would fire as needed -- ideally through a buffer tank.



Single speed pumps make sense for non-zoned systems, but if there is any kind of zoning (whether it's TRVs, zone valves, or more sophisticated proportional valving) then a variable speed circ is best.  Fortunately, those are cheap and widely available now -- your hypothetical 5,000 sq ft project would be be a perfect fit for a Stratos, an Alpha, or a BumbleBee.