flow control for continuous operation

Brad White

Depending on the manufacturer, the worst-case installation is that you install HWS and HWR temperature transducers or a delta-T setup with a sensor on each pipe. As the temperatures depart or narrow, the proportional output signal (4-20 mA, 0-10 VDC, etc.) is sent to the circulator controller to speed up or slow down the flow rate.

I say "worst case" because some, such as Taco, Wilo and Armstrong, do this internally, at least on pressure. Not sure of how each does it for themselves but no external sensor is required.

Traditionally, a Delta-P arrangement has been used but with the newer technology, temperature is a direct effect solution. Either pressure or temperature work the same, with a variable proportional signal.

Constant differential pressure (Delta-P) is a skewed value, assuring that your pump is not creating more pressure differential than necessary (not a bad thing in itself!).

But at the end of the day, is it not better to know that your heat is being extracted for the cost of moving the water in the first place? I can easily see that a constant delta-T controlled circulator will run more slowly than a constant delta-P controlled circulator. What does the pressure know about temperature?

Bupkes.

steve_157

flow balancing

I am installing new baseboard radiators and pex-al tubing in my home. I have the tubing pulled and was planning to use a copper 1-1/4 header with 7 parallel loops and TRVS for room by room control. I plan to use a single pump with a Tekmar 260 for outdoor reset control of the system (and a separate small pump for an indirect water heater). My question is how do I balance each loop? do I need to insert balancing valves within each loop? will the trvs do that for me given they have thermostats and regulate flow? do I install globe valves and set up each loop?

Unknown

Steve,

are you worried about dead heading the circ as the TRVs close?(you should be). Use a pressure differential valve like this and just make sure your pump can handle the longest circuit, adjust-it accordingly and you`ll be fine.

Globe valves really have no place on a hydronic system, too much resistance/turbulence to flow.

Dave

steve_157

re flow control

that is very good news, thanks! I was just concerned about imbalance which would produce poor heat in some zones because all the flow is in another loop. It sounds like I just need to ensure my highest head loss is covered, install the differential pressure valve and make sure I seek out a rather flat pump. how would you rate the grundfos, taco and bell gossett in order of 123?

Unknown

Steve

Make sure your circ can supply the flow to all the combined zones at once, then has the head to do the longest. As your TRV`s start to close, the PD valve (properly adjusted), will balance the flow.
My preference is the 3 speed Grundfos OR Taco, great for tweaking.

BTW- Are you installing 1 TRV for each loop?,,or 1 TRV for each rad?

Dave

Brad White

A slightly different view

This is not to detract from Dave's excellent advice in any way, but I have been evolving in my thinking as technology catches up (or rather trickles down) to the residential level.

Essentially, TRV's will be self-balancing so long as you have sufficient head to reach your furthest radiator (just as Dave pointed out).

A DP bypass is indeed a tried and true method of leveling out pressure spikes when the TRV's are mostly closed.

My personal "first choice", in light of the technology, is a variable speed (not adjustable 3-speed) circulator. Taco, Grundfos and of course Wilo and Armstrong make them in various degrees of selection across their lines. There are more I am sure with more to follow.

Anyway, my preferred set-up would be to have TRV's on all emitters* and the circulator set up for Constant Delta-T. It is all about temperature after all...

With the circulator set up for constant delta-T, say your water leaves at 140 and comes back at 100 on a cold start-up. The flow will increase to maximum to effect warm-up (rare in constant flow systems but only to illustrate). Now, as the building warms and TRV's close down, the S to R delta-T will begin to narrow, leaving at 140 and returning at say, 132 degrees. The circulator will slow, assuring cooler water than otherwise would occur. Less electrical cost too, overall.

I am not saying that the circulators are yet price-competitive but for superior control and eventual payback, what is not to like?

My $0.02

Brad

steve_157

flow control

trv for each loop is what I had planned. issues?

Rich L.

Control?

Is the circulator actually reacting to the temperature differance of supply and return? Are there also pumps that can be set up to react to the pressure difference as zones open and close off?

Thanks, Rich