Buffer Tanks

servicetech

Hello - I have an application where two wall mount, low mass condensing boilers are serving a make up air ventilation unit with hydronic coil and a water coil unit heater used for space heating. The load for the makeup air unit is 254 Mbh and the unit heater is 60 Mbh. The primary system is configured with a dedicated boiler pump serving each modulating boiler. The secondary system, also a low mass system, houses the MUA unit and unit heater and is served with a single circulator.

My question focuses on the low mass application. I was planning on decoupling the boiler loop from the secondary loop with a low loss header. The boiler loop hold approx 20 Imp gallons and the secondary systems holds approx. 35 imp. gallons. Is the low loss header enough, or should a buffer tank in the secondary system be considered. Currently, the boilers can modulate to match Btuh demands of the mua unit and the unit heater?

Thanks in advance

servicetech

CMadatMe

Cascading

What are the modulation rates of the boilers and will they be cascading? Whose mod/con are you using?

Brad White

You can also

combine the buffer tank with a hydronic separator, such as a Boiler Buddy. A large tank with large taps to do double-duty.



I think what you are finding is that make-up air units and unit heaters, being low mass and with rapid transfer (moving air) require a relatively constant flow of water. With low mass boilers, this can lead to short-cycling when demands are sudden/immediate, so having a hydronic piggy-bank makes sense. That is, if I gather your application correctly.

JohnNY

Hi, Brad.

I'll tell ya'. I like that Boiler Buddy, but the one-year warranty scares me.

Brad White

Hey John!

One year warranty?? I did not know that. Too bad. I wonder why that might be, so will ask HTP.



I think instead of specifying a time-based warranty, I will just ask that the warranty be longer than one of Charlie Sheen's tantrums.



Thanks, John- you got me thinking as usual.