fooling a 007 variable speed delta-t pump

[davem3261]

I will soon be purchasing a gasser to replace my energy mate wood boiler. I will be using nofossil piping schematic where there is a pump for the wood boiler and storage and another pump for the loads. I would like to use a taco variable speed delta t pump. But it wont work like i want it to. Out of the box I can't find a variable speed pump that will give me a 180 constant output. My goal is to have a constant 180 degree temp coming out of the boiler. Could I put the appropriate resistor for say 160 degrees in place of the return sensor. Set the delta t for 20 degrees. That should give me a constant 180 output. If the output increased to 185 it would see 25 degrees delta t and increase pump speed until it dropped back to 180. If the output temp dropped it would see a lower delta t and reduce speed. If you don't think this will work please advise on a better plan.

 

[ewdudley]

Welcome.

(What is your plan for return temperature protection?)

There's no need to get hung up on variable speed control. There is no disadvantage in using an on-off control with an aquastat, pump on at 182 degF (or whatever), pump off at 178 degF (or whatever). Many boilers have a 'launch temperature' setting that will do what you want.

 

[davem3261]

For return protection I was going to use a zone valve controlled by an aquastat

 

[BoilerMan]

For return protection I was going to use a zone valve controlled by an aquastat

You will not have good success, something able to modulate or short-circuit the boiler's supply water will give much better results and be simpler.

TS

 

[ewdudley]

You will not have good success, something able to modulate or short-circuit the boiler's supply water will give much better results and be simpler.

TS

I think all return temperature protection schemes rely on recirculating supply water back to the return port and then mixing in cooler system return water.

The two most common types of setups are a single pump with a mixing valve circuit; or a dedicated recirculating pump on a boiler loop, and an injection pump on an injection circuit.

A mixing valve can be motorized, or most commonly, simply thermostatic. Supply temperature can then be controlled with simple bang-bang logic, or with a reverse-acting variable speed control, or not at all once supply temperature reaches the 'launch' temperature. There is a variation of the Taco VS pumps that will do reverse-acting setpoint control, but as I claim above, in this situation bang-bang control meets the requirement while being simpler, more reliable, and more economical.

With a boiler loop plus injection it's more difficult to control both return temperature and supply temperature. What works pretty well is to simply control return temperature to X while knowing that normally if return temperature is X, supply temperature will be X plus deltaT. Here again bang-bang control will do the job simply and economically, but typically you need a higher re-circulation flow to accommodate the intermittent injection flow, which results in a return port temperature that is higher than necessary, which could decrease efficiency at higher firing rates.

The ideal injection loop system would have a reverse-acting variable speed control on the boiler loop pump to maintain supply temperature to setpoint, and another reverse-acting variable speed control on the injection pump to maintain return temperature to its setpoint.

 

[maple1]

I think all return temperature protection schemes rely on recirculating supply water back to the return port and then mixing in cooler system return water.

The two most common types of setups are a single pump with a mixing valve circuit; or a dedicated recirculating pump on a boiler loop, and an injection pump on an injection circuit.

A mixing valve can be motorized, or most commonly, simply thermostatic. Supply temperature can then be controlled with simple bang-bang logic or with a reverse-acting variable speed control. There is a variation of the Taco VS pumps that will do reverse-acting setpoint control, but as I claim above, in this situation bang-bang control meets the requirement while being simpler, more reliable, and more economical.

With a boiler loop plus injection it's more difficult to control both return temperature and supply temperature. What works pretty well is to simply control return temperature to X while knowing that normally if return temperature is X, supply temperature will be X plus deltaT. Here again bang-bang control will do the job simply and economically, but typically you need a higher re-circulation flow to accommodate the intermittent injection flow, which results in a return port temperature that is higher than necessary, which could decrease efficiency at higher firing rates.

The ideal injection loop system would have a reverse-acting variable speed control on the boiler loop pump to maintain supply temperature to setpoint, and another reverse-acting variable speed control on the injection pump to maintain return temperature to its setpoint.

But none of that incorporates a zone valve as mentioned above - I don't think?

 

[ewdudley]

But none of that incorporates a zone valve as mentioned above - I don't think?

Not normally anyways, although for variable speed injection you could use a deltaT ECM pump and a 555 series Taco wax motor valve.

A PID controller could be used to control an SSR that would keep the valve partially open. But the Cv on the zone valve is low and they want $150 for a 555 these days, plus the controller, SSR, and pump. So not really a practical alternative to a conventional mixing valve setup or bang-bang injection.