Piping ?

[Rlankford2]

I am starting my piping in the house and was wandering what if anything needs to be changed with my piping.
the first zones is DHW thru a flat plate exchanger the second is a Water-to -Air in the furnace. zone 3 and 4 are under floor radiant and in floor radiant.

one question i have is how to get the furnace to fire if the boiler temp is low or dose not reach a set temp thru the exchanger.

 

[ewdudley]

I usually recommend a buffer/hydraulic separator in situations with one or more hot loads plus low temperature radiant. BHS tank could be a 30 gal propane tank, 10 gal 'RV' propane tank, two feet of 3" pipe, any small tank with 18" or more of side wall that you can add fittings to.

This makes it easy to maximize stratification in storage.

The aquastat in the side of the tank is set control the transfer pump from storage to BHS tank in order to maintain a minimum temperature that will satisfy the WAHX.

Since the WAHX draws from below where DHW draws, DHW gets priority.

The low temp loads draw from the bottom of the BHS tank, which gives the system the opportunity to lower the temperature of the DHW and WAHX return water before it goes back to storage.

To control switch-over to furnace heat you can add an aquastat to the top of the BHS tank, or to the manifold at the top of storage.

If you sharpen your pencil and run the numbers I wouldn't be surprised if 1" pipe was big enough to draw from storage.

(BHS tank in drawing is missing vent in top and drain in bottom.)

 

[Rlankford2]

ewdudley thanks for the replay

I may be able to squeeze in a 30 Gal tank in the piping area. very limited space there for a tank but i like the idea of being able to use the lower temp water for the radiant.

 

[ewdudley]

I may be able to squeeze in a 30 Gal tank in the piping area. very limited space there for a tank but i like the idea of being able to use the lower temp water for the radiant.

The optimum BHS tank size depends on the size of the radiant loads relative to the high temperature loads. Ideally there would always be some reservoir of 'spent' water available for the radiant loads during the times when the storage-to-BHS transfer pump is not running. If you figure out how much spent water the high temperature loads will generate per heating cycle and then figure out how much spent water is likely to be used by the radiant loads while the high temperature loads are idle you can get some idea of what size tank might be optimal. Also you could add a timer than would enable the radiant loads for a certain amount of time during and after the time the transfer pump is running, which would keep the high temperature and radiant loads synchronized.

But a tank smaller than optimal might still make plenty of difference, enough to be worthwhile. A simple five gallon BBQ propane tank with a single port in the top and a single port in the bottom would do the trick if space is tight.