VARIABLE SPEED CIRC VS. TEMPERING VALVE FOR BOILER PROTECTION

[91LMS]

what is the best way to go? a variable speed circ would still allow cold water to return in the event of startup where a tempering valve would not correct? running a conventional boiler i am wondering how critical this will be for me but could see how it could improve efficiency as well if the boiler doesnt get shocked with cold return temps.

 

[ewdudley]

what is the best way to go? a variable speed circ would still allow cold water to return in the event of startup where a tempering valve would not correct? running a conventional boiler i am wondering how critical this will be for me but could see how it could improve efficiency as well if the boiler doesnt get shocked with cold return temps.

When I was re-piping to connect to the wood boiler I took the opportunity to implement return temperature protection for the oil boiler.

Our house is a converted steam system with big radiators and a lot of two inch return piping, so we can get a bunch of cold water as different zones are activated and as they cycle, so what I did may not be applicable to your situation.

At any rate, I just put a recirc loop on the oil boiler with it's own circulator that runs whenever the burner is running, and whenever there is a call for heat. It goes from boiler supply straight back down to boiler return with a 007 to run it. And of course load supply and return are teed-into the loop with their own circ(s).

Then there's an aquastat on the boiler return that disables any load circ from running if return temperature goes below 150 degF (or whatever) and until return temperature rises above 160 degF (or whatever).

So cold return water gets mixed in with the recirc flow to prevent shocking, and the boiler stays hot from top to bottom. The aquastat and 007 were salvage components, so it just cost the time and the fittings and works quite well.


Or a tempering valve would definitely work nicely as well.


In any event, as you suggest, the variable speed circ would have no way of preventing un-mixed cold water from filling the bottom of the the boiler.

 

[91LMS]

thanks ewdudley.... noboby else has any input or preferances on this?

 

[slowzuki]

I'm a fan of the variable speed circ, with the right controller you can prevent the boiler from dropping under 140 F and simplify the system. Last I checked a couple of years ago though the controller like that is a lot of money.

I'm not concerned if my boiler gets cold water returning unless its pulling the water jacket to under 140 F and giving me condensation inside the fire tubes.

 

[stee6043]

Someone vastly sharper than I could correct me if I'm wrong but I do not believe a variable speed circ can effectively replace a properly plumbed bypass loop and a mixing valve. The bypass loop/mixing valve concept is critical to both maintain proper return temp and insure you gradually increase flow to the system as system return temps rise. I don't believe you can effectively accomplish both with a single circ no matter how fancy the controls.

 

[in hot water]

Most of the tekmar controls have boiler return protection in them. Basically the control "watches" the boiler temperature with a sensor. Once the temperature drops below the acceptable temperature you put into "boiler min" the pump or valve can modulate, stop, or vary the speed of the circ. The system needs to be piped properly, and a dedicated pump or valve for this to work.

I did the same with a solar ∆T control . The boiler pump starts only when then boiler reaches 145F. The hotter the boiler temperature the faster the pump revs up. When the fire dies, or goes out, boiler temperature drops, the pump revs down to a slow as 30% then stops.

hr

From the tekmar website:

 

[91LMS]

so in that case you are talking using a controller and not necassarily depending on a tempering valve or variable speed circ standing alone?