Performance curves for TACO 0011-VDTF4 circulating pump

[bkspero]

My son's HVAC contractor has proposed that he replace his single speed boiler water circulation pump with a variable speed pump controlled by the delta T of the water across the hot water coils. They have quoted a TACO 0011-VDTF4 3 speed delta T pump.

Does anyone here have the performance curves for that pump? The TACO website has curves for the 0010 and 0012 models, but not the 0011. It does have a separate page for the 0011-VDTF4, but that page links to a data sheet with performance curves for their single speed pumps only. Online sellers offer that pump, but they, too, have data sheets for it which only contain curves for single speed pumps.

 

[Geofd]

Whats wrong with his single speed pump.

 

[bkspero]

Whats wrong with his single speed pump.

I don't know for certain. This variable speed pump is what the HVAC contractor quoted. The symptom is that the largest space heated by the boiler does not reach a comfortable setpoint on very cold days.

The boiler feeds hot water coils in two different heating zones (air handlers) plus a coil in a Triangle Tube indirect fired water heater. Each zone is controlled by its own zone valve. On cold days when both heating zones are calling for heat the water delta T across the larger zone coil is 40-50 degrees F (there was one reading of an 80 F delta T). The performance data for that hot water coil indicates delta T's there at max output should be about 20 degrees with 9 gpm of hot water flow (I could be wrong about the exact numbers, but it is much lower than he is seeing). During these times the boiler is running relatively short cycles to maintain the boiler water at its setpoint of 195 degrees F (that's as hot as he is comfortable running it). About 2-2.5 minutes burner on to reach the setpoint, then 3.5-4 minutes off.

They are planning, I think, to increase the water flow rate to the larger coil to increase its heat output and utilize more of the boiler capacity. But avoid having too high a circulation rate to a smaller zone when the other smaller zone and the larger heating zone are not calling for heat. At least that's my speculation.

Should the contractor be using a single speed pump? Maybe a larger one than the TACO 007 currently installed?

 

[Geofd]

If this has been a condition that's always been there. Was it sized correctly when installed????? How are your windows+wall insulation

 

[bkspero]

The house is a mid century modern type with heat loss problems due to both window and roof insulation deficiencies. The HVAC system was upgraded to heat pumps a couple of years ago by the prior occupants, but it was not sized properly for reasons that are too complicated to relate here. The boiler was to be used as aux heat.

My son has worked on its reconfiguration for the past 2 years and has now gotten it close to keeping the house at a comfortable temperature on all but the coldest days (primarily by setting the system to use the boiler as primary heat). His hope is that increasing water flow rate to the hot water coil in the larger zone air handler will increase the heat output to that zone and close the last shortfall. The HVAC contractor specc'd the subject pump for that purpose.

BTW, my son got in touch with TACO and was told by them that they did not have the partial power performance curves for the 0011-VDT pump.

 

[GReynolds929]

Are there balancing valves or flow control between the two AH coils?

 

[bkspero]

Each hot water loop branches off the main supply line to 3 valves. In order, a ball valve, a Honeywell zone control valve (I have a photo of 1 showing a model #V8043E1012), and a manual gate valve.

I believe the zone control valve is only on-off, so the answer to your question is, I think, no. Unless the manual gate valves can provide dynamic balancing in a way I don't see.

 

[Geofd]

I keep going back to post #5 should you 1st address your heat loss issues????? Just my opinion/thought
..

 

[bkspero]

I appreciate your input, but don't see the logic. They were told that upgrading the windows (one is a window wall) and insulating the house would essentially require a very costly gut renovation. Mid-century modern houses were not designed for utility and servicing.

You've seemed resistant to my son's decision to increase the water circulation rate to the larger zone hot water coil? Do you think that it won't increase the heat output of the system to the living space and its just a waste of time? Or do you think that there are safety issues? Or operational issues (like the boiler is likely to have a short lifetime operating at near 100% capacity)?

I'm curious. You've asked questions and made recommendations, but haven't really shared your reasoning as to why you don't think his plan makes sense. Would you do that?

 

[Geofd]

No not resistant at all, just suggestions, I had insulation blown in in 2 different houses, I just thought if you got the air leaks addressed 1st, see how that works and how from there...

 

[bkspero]

Thanks for letting me know.

 

[MicEd69]

I'm not following how a variable speed pump will solve this problem.

The control valve to the larger zone should be fully open when maximum heat is being called for. If the design for the water side of that coil is 20 degrees F delta T at 9 gpm based on an inlet temperature of 195 degrees F and he is experiencing over twice the temperature drop on the water side, the water flow must be way too low assuming the air flow is typical house HVAC conditions. So, the water flow rate needs to increase to get to design conditions. If the existing circulating pump is too small, why not replace it with a larger pump and eliminate the problems that he will experience with a variable speed motor.

And based on your description of what is happening, the existing circulating pump may indeed be too small. As the return water from the larger zone is cooler than the design temperature based on the high temperature drop across the coil, the boiler should be firing longer cycles instead of shorter cycles. As it is able to heat the water back up to 195 degrees F in a short period of time in the "fire box" could mean that the flow rate through the boiler is lower than the design flow rate.

Based on your descriptions, a larger single speed pump to bring the entire system up to design conditions seems to me to be the better solution. The control valves to the various zones will control the water flow rate so the larger pump will only produce the water flow rate as required to meet the conditions in the zones. And as the power required to pump is based on the flow rate through the pump, a larger single speed pump will not take more electricity than a variable speed pump to operate this system.

Without being there and seeing everything, this is my input to your son's issues. Of course, all this assumes that the system is not fouled with mineral deposits, and everything is in good operating condition.

 

[bkspero]

MicEd, the proposed 0011-VDT pump is larger than the current 007. So at full power I am presuming that the HVAC contractor believes it can achieve a 20 degree F delta T when all 3 zones are calling for heat (just as a 0011 size single speed pump would). And if the pump at max output is slightly oversized and produces less than a 20 deg F delta T, the variable speed pump is able to slow itself down to reach 20 F, where as a similarly sized single speed pump will continue to operate at a higher than optimum flow rate and produce a delta T of below 20 F.

The problem it also addresses, I think, is that it can maintain that 20 deg F delta T even when only one of the smaller zones is calling for heat. And avoid operating that single zone at an extreme high flow rate and a low delta T. Plus it will, I think, save a few pennies in electricity cost when pumping at the lower rate.

The only downside that I see with the variable speed pump is higher pump price, and on the scale of HVAC parts and labor costs it is not all that much.

That is unless there are other problems with variable speed circulator pumps that haven't been discussed? Do you know of any?

 

[MicEd69]

OK, I went back and re-read post #7. I missed the last sentence that said the zone control valves were on-off only.

So, I now see what they are trying to do. As long as they keep the flow rate below the recommended maximum flow of the water to avoid erosion issues on the water side of the coil, it should work.

In my opinion, a much better engineered solution would be to use some flow control valves for each zone and a single speed pump. But I don't know if there is easy access to the piping or if the control changes would be a problem or what the cost impact would be. It would just be a much better system, IMHO.

 

[bkspero]

Access is a problem. Could be done, I think, but not easily. I can see why they quoted the variable speed pump and not flow control valves.