constant circulation control options

Randy Tibbits

I have a apartment complex that I service. Their system consists of constant circulation with danfoss thermostatic valves. The boiler has a remote bulb thermostat that functions as a warm weather shutdown. The boiler runs full bore when the temp is lower than remote bulb t-stat. This seems like such a waste. Is there a control method that would be benificial to my customer? Thanks

Mark Wolff

Boiler reset

Tekmar control with outdoor reset should work fine to control boiler temp.

Randy Tibbits

Thank you for the info. Is there a control that will vary the speed of the pump depending on the number of zones calling? I know the trvs don't have a end switch but I wondered if there was a control that can sense a pressure drop and would vary speed to compensate. There probably is'nt enough of a energy savings with a control like this. But I'm always wondering about things like this.

The tekmar reset control. Is there some average percentages of fuel savings that can gained by using reset? Is there an average payback period?

ScottMP

Randy

15 to 25 % numbers are thrown around alot by most companys. We did the sam eset-up and with great results. We used a Tekamr 360 and used constant demand for the circulator.

How about a preasure differential valve to keep your job simple. This would by-pass back to the boiler when only a few rads where calling.

Scott

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Jerry Boulanger_2

Temperature reset and variable speed

pumping are generally not a good idea to use together. If the reset schedule is correct, more TRV's will be open more often, resulting in a higher average flow rate and defeating the benefit of variable speed pumping. If you're going to use one or the other on smaller systems (generally under 3-5 hp pump), use reset control. It is easier and less expensive to install and operate.

Steve Eayrs

Not sure why you would think reset and injection do not work good together, when most injection controls also do boiler reset at no extra cost. Maybe if you are working with gas only, or condensating boilers, but the oil-fired world is full of reasons to use both.
Why not reset the boilers as long as they maintain the min.'s they need to and at the same time be able to mix down, (injection pump), to more accurately meet the heat demands?

Doesn't have to be radiant floors to see the benifit. Have done this on a couple apartment buildings, w/ baseboard heat zones, using tekmar injection control (believe it may have been a 365), and also used 368 zone controls and rtu's. Saved aprox. 15% in fuel per year, and made one happy customer.

I just had to edit this and add that I am not talking about variable speed system pumps, but injection into a pumped secondary. You may be talking about the other?


Steve



Steve

Unknown

I believe he was varying the zone pump,

rather than varying an injection pump into the zone.

He didn't say reset and VS Injection wouldn't work together, he was slowing the zone pump when TRVs are closed.

Noel

Jerry Boulanger_2

I was indeed referring

to using variable speed distribution pumping in tandem with reset water temperature control.

Mike T., Swampeast MO

If your radiation is well-balanced with TRVs and you're using an accurate reset curve you're best off with a relatively constant rate of flow to keep the TRVs "happy" and not "hunting".

Is that what you're getting at, Jerry?

Randy Tibbits

The reset control and the pressure differential valve sounds like a great application. Thats what got me wondering in the first place. Few or no TRVs calling and the circulator moving hot water around this ten unit apartment house. All the piping is concealed except for one 1 1/2" supply pipe and ten 3/4" returns. Where can I find more information on the PDV? In other words I need to learn more.

Jerry Boulanger_2

Not really, although you are correct

about the control - constant flow/variable temperature gives great control. My point was that with a good reset schedule you should get more or less constant flow, which defeats the purpose of having variable speed control on the pumps because they wouldn't likely slow down much. Variable speed pumping really shines on distribution systems that have highly variable flow - all 2-way valves and a constant water temperature.