Knight Piping

martin

I'm doing a radiant job with 3 larger zones and 4 small zones. I'm running it with a Knight and even with modulation the small zones if on by themselves will be toto small of load for decent run time. So am thinking of using a small buffer tank. My ? is does someone make a small insulated tank with proper tapings and such. Also rather then individual pumps on each zone I'm thinking maybe using Zone valves and a variable speed circ. like a Wilo, any input would be appreciated

Brad White_200

Buffer Tank

HTP (The Super-Stor folks) make an insulated SS tank with 1.5" tappings.

(I wish they had this years ago or I missed it, but my HTP coil booster tank works fine just the same.)

I would size the tank for at least five minutes of total flow time. In other words, if you are flowing 6 GPM, use a 30 gallon tank. Not scientific, just a benchmark place to start.

Personally, I like the ability to take the tank on-line and off-line using a main valve. There are a dozen ways and strategies to use though. Others I am sure have better ideas.

You can also size the tank using a more detailed formula based on run time, tank average temperature and loading. Siggy has a module in his HDS software that does this nicely.

The use of zone valves (so long as all zones have them) with a Wilo circulator is a wise choice. Too many pumps can add up in electrical consumption.

Ted G

HTP

It is an SSU-20B. It has
4-1 1/2" ports,
1-1/2" vent port,
1-aquastat well.

martin

? for Brad

By taking it off line I take it you are not heating it when using a larger load , would you gain anything tremendous by doing this other than more controls. HTP is heat transfer products isn't it.

Brad White_201

HTP

is Heat Transfer Products in Freetown, MA, but a good guess on your part.

The way I take my buffer tank on and off line:

I place the tank on the return side so that I do not have to wait for heat from a cold start. Rather than tell you how I did it on the fly out of desperation, I will tell you how I would have done it if I had more time to think about it.

Picture the return main going back to the boiler, after picking up the last radiator.

In this main is a full-port motorized ball valve with a full-size tee on each side of it.

With me here so far?

The tee branches on each side of this valve run TO the buffer tank from the inlet side of that main valve, and comes back FROM the buffer tank after the outlet side of that main valve.

Now, upstream of all this, is a strap-on aquastat.

When the return water comes back too warm (say 120F), the aquastat closes the valve, forcing water to go out to the tank and back in to the system. A diversion!

Now the water that was sitting in the tank is cool, having sat there since the last Clinton administration. That slug of cool water (30 gallons in my case or six minutes of flow time), goes to the boiler and keeps it running a bit longer.

When the boiler cycles off, this reservoir of stored energy is depleted over the next few minutes.

When the return water again cools, the valve closes and the tank is taken off-line.

You can see that one does not have to keep the tank hot (as it would be on the supply side). Also when the boiler fires, the radiators see that hot water first without having to wait for the tank to warm up.

martin

Thanks

Got heat tranfer after googling super stor thank you

martin

1 more ?

who mfgs motorized ball valves

hot_rod

Boiler Buddy

is another buffer option. Caleffi has motorized ball valves, keep in mind motorized ball valves need to be motored open and closen. They are not spring return, so you need a control that is able to operate open and close.

A 3 way zone valve may be a better choice?

hr

Brad White_200

Ball Valves

Caleffi as hot rod suggested, but any ball valve manufacturer, (Watts, Conbraco/Apollo, Neles-Jamesbury), have models which accept motorized heads.

Personally, I use Belimo. Key in your case is "full port" so that the pressure drop is low. If not, some flow may be forced through the tank like it or not. If in doubt, go up a size and keep those "tees to the tank" close-by that valve.