Cold start CI boiler and P/S piping

[Deleted User]

HR -

Right now, the system is using a thermostatic mixing valve to temper supply to the floor. Nothing fancy at the boiler as there is still high temp copper tube BB in use. However, as part of renovation, BB will be replaced. I was hoping to oversize the BB and use lower temps in the renovated rooms.

From everyone's responses, it seems I would need some sort of control at the boiler to deal with the lower return temps and condensation. It seems a "cold start" boiler and/or P/S piping will not address this issue.

What should I be asking for or looking for when getting quotes? Thanks again!

[Deleted User]

Cold start CI boiler and P/S piping

Would a cold start oil boiler (like the Biasi b10) need P/S piping or is it designed to handle the low temps? Would P/S piping have any benefit at all? thanks. -jd

Brad White_184

The advantage I see

in P/S with an oil-fired boiler is the decoupling of flows, the isolation from the colder return water.

Specifically, I would set it up with a boiler circulator and smallest volume loop (tight near-boiler piping). The radiation-side circulator is obviously independent by definition. Then I would use a variable injection circulator such as a Taco 00VR which would respond to maintaining the radiation loop temperature while keeping a finger on the boiler return temperature with a sensor dedicated to that function. Simple.

In the alternate, a Taco 4-way i-Valve is another simple way to achieve this using fewer circulators. It too has a boiler return sensor. You need that sensor, remember.


Absent these methods, using an aquastat delay, blocking boiler supply until the boiler return temperature was established well above dewpoint, that used to be the way to go. In so doing, the colder system-side return does not come back but you burn fuel while waiting.

You can still do this but the above products can do that automatically with few components and affords you constant circulation and a modulating rather than on-off effect on protecting the boiler.

My $0.02 anyway.

hot_rod

What's it connected to?

if it is a low mass copper tube baseboard the cold start is generally not be a problem.

A radiant slab would be a high mass emitter and could easily have the ability to keep the boiler below dew point for extended periods.

P/S alone doesn't protect the boiler. The boiler can only be protected adequately, by sensing and reacting to the return temperature at the boiler return piping. Anything else is a guess.

Luckily there a dozen's of ways to accomplish protection via control, piping, etc.

hot rod

[Deleted User]

thanks-

I have about 2000 sq ft on a staple-up radiant floor. Upstairs, the btu load is low and I was planning on oversizing copper tube baseboard to keep design temps low.

All the quotes I'm getting don't detail how the new system will handle the low return temps. I thought P/S was a way to handle this...from what I have read (not from experience!!).

When reviewing estimates, should I be concerned with this level of detail? In otherwords, is controlling return temps a no brainer that everyone does, or should it be a line item b/c there is an expense associated with it?

thanks again.

hot_rod

Often times

the mixing device used for the radiant mix down temperature has the boiler return feature built in. It may not be noted in your estimates.

If it shows brands or model numbers you could search it out. I believe all tekmar mixing and boiler controls have return protection functions. Taco, Uponor, Watts Radiant, Honeywell, most all do. Many use tekmar controls with a private label.

hr