delta t vs delta p circulator control

PORKCHOP

i have read several post on the taco variable circulator vs the grundfos alpha pump,  one uses the delta t the other uses delta p to control the flow depending on how many zones are calling.

it sounds like the delta t approach is a better approach to maintain comfort level throughout all zones.

has anyone had some previous experience using either pump, what type of results and satisfaction

we will be using the pump in a radiant floor application that will have 9 zone valves with one circulator

what is the minimum gpm that the variable circulators will operate at?

Harvey Ramer

I have used both and both are unique in their

ability to perform a specific task. One is not better than the other. You have to pick the right one for your situation. From the little you have posted on your system I would tend to think the delta-p would serve you best. You don't have to worry about minimum flow rate with it. You can dead-head it.

Gordy

delta t vs delta p circulator control

If you are using zone valces the a delta p circ is what you need unless you all ready have a differential bypass valve installed on the system. The delta P will adjust its flow rate based on how many zone valves are open or closed.

PORKCHOP

delta p vs delta t circulators

yes i am using zone valves and have not installed any differential bypass, i was hoping that the circulator would adjust flow to keep from having to install the bypass

thanks for your input  

gennady

Pump

If you have TRV then you need delta P pump, if you. Do not have TRV, then you need delta T pump. If you have zone valves use delta P pump

Joe Mattiello

Delta T pumping

Arguably, the Delta T pump is always better.  In the most simplistic way the delta T or Delta P pump will satisfy the load while adjusting the flow to accommodate the dynamic system characteristics when zoning with zonevalves.

However, there are other considerations, for example, the impact on a modulating-condensing boiler, and the amount of run-time the boiler spends below the point of flue gas condensation. This of course affects the efficiency of the boiler. 

For your reference and a thorough explanation of the difference of Delta T, and delta P, I have attached a white paper I had. Let me know what your thoughts are. 

Gordan

Doesn't seem quite right

Firstly, delta-p is really best applied with proportional flow control based on zone feedback - read, TRVs. There, it is the TRV's job to throttle flow based upon what the zone actually needs, and this happens on a per-zone basis rather than system-wide basis. The delta-p circulator only responds in order to ensure that changes in flow in one zone do not affect the flow in other zones. It does not care about load.



Secondly, trying to infer the load on the basis of the system's delta T does not seem much, if any, better than trying to infer the load on the basis of how many zone valves are open. Let's say that we turn down flow and delta T still does not widen to our design value. Is that telling us that we should turn down flow even lower because, "obviously", the system is overpumped for the conditions? Or is it perhaps telling us that our emitters are simply not able to dissipate the needed heat at this flow and supply temperature, and we're making matters even worse by throttling the flow further?



Thirdly, if the boiler's reset controller is telling the boiler to maintain a given supply temperature, but that temperature is high enough where we feel that we should reduce the supply of heat to the emitters by throttling flow to the system, then there's room to turn down the supply temperature, in the first place.



These are just a few of the things that stood out to me as perhaps being based on unwarranted assumptions.

chapchap70

Small Zones

I've only had a chance to use one "delta p" circulator for two zones (zone valves) that were an afterthought to the heating system.  The boiler is way big for the two small zones and is cold start cold finish with a purge control. (System 2000) 



I tried the Alpha for this application because I needed the maximum BTU's to the zones to get as much heat out of the boiler as quickly as possible so I thought that 4 gpm per zone would get me maximum output.  I do not believe there is any way I can get a 20 degree Delta T out of these small zones with how this system is.  The display reads mostly 4 gpm but sometimes goes to 3 for short bursts of time.  When both of the small zones call, it reads 8 or 9 gpm.  I don't think a delta T circulator would work as well for this situation because I think the circulator would try to lower the flow rate if my understanding is correct.



I don't know what the flow rate would be if I just stuck a 007 in with one zone open or two.  The piping is 3/4 inch (as compared to 1 1/4 inch for the other two heat zones each having their own circulators).  I do know that there is a little less electricity used by using the Alpha.

SWEI

agreed

Delta-P (or delta-PV) control is tailor-made for distribution loops with multiple zone valves, whether or not the valves themselves are are proportional.



Delta-T is ideal for single HX loops that do not have control valves (changing flow) in them.  Boiler primary loops are a prime candidate here.

bill_105

T or P?

This topic is actually a rehash of an old thread.

Back in 08 or 09 some guy complained of noise coming from a noisy Taco VDT Circulator. After that issue wore itself to an end the issue of delta t or delta p became the issue de jour. (for a week)Then along comes some guys you tube thing and later the white paper thing. Now I had just put in my very first Taco VDT and was reluctant to install another.

To keep a long story short, I had a new system in progress which had a real big loop and a very short loop, also some others.

So say you had a 40k loop and a 6k loop, on the coldest day the big one would want full speed ahead from the VDT pump but the little loop would ask for a much slower speed.

So when the two water temps got together at the the boiler what's the sensor to do?I"ll just leave it at that

BTW I think it was ME that got that all stirred up back then. Where is he when you need him? He does a better job of stirring up the pot than anyone:)

Gordy

System control

I will just say that circulators can not be the magic wand for poor installation strategies/ practices. Along with piping practices. The smaller the circ the less energy used. The way to a smaller circ is through proper dia pipe, and getting away from rediculous loop lengths.



In my mind the best circ would be one with logic which would allow delta t, delta p, or a selection of 3 speeds, and ecm. All wrapped in to one circ you make the call in the field which way to go for the system. More expensive yes. But think of the shelf space you could clear out.

SWEI

best circ

I'm pretty sure Taco has all those options in the BumbleBee.  Too bad they only offer it with 007 hydraulics.