Two Pipe System Design

Whizzer

I am installing a two pipe hot water heating system for 8 Radiators and one kick space heater. Each has its own thermostatic control. The total is about 60,000 BTU. The main runs are 1 inch and I am using a 1/2 inch branch feeds to the radiators with a mono flow tee in the return.

When I end the supply at the last heater do I need to tie it in to the return? (When all the radiators are off the circulator will dead head if I don't).

Do I need to put balancing valves in the return pipe from the radiators. (There will be 3ea 48X16, 2ea 40X16, 1ea 40x12, 2ea 12x72 and a 8400 BTU Kick Space heater tied to the system)

Mark Eatherton

I see possible issues....

I like your thinking, but, with Venturi fittings, when you stop the side branch flow (TRV's closed) the pressure drop in the main increase significantly.



Ideally, you should use a DCECM variable speed, constant head circulator. It will be able to see when all valves are closed, and will maintain minimum energy consumption awaiting the load.



If you are confined to having to use a fixed speed circulator, then you will want to incorporate a pressure activated bypass between the supply and return sides of the system. Depending upon where you put it, it could cause some areas to over heat. If you put it at the end of the supply main, connecting it to the return, now all the distribution supply piping becomes an uncontrolled radiator. If you put it between the pumps supply and return, it will negate any unwanted distribution gains, and will keep you from dead heading a pump.



I assume you will be using a high efficiency heat source with outdoor reset for the utmost in efficiency?



ME

Whizzer

Two Pipe System Design

Thanks for the feed back.

I will put in a pressure activated bypass at the beginning of the loop. I will connecte it before the first radiator on the supply side and after the last radiator on the return side.

Will I need a balancing valve at each radiator? A lot of work if I don't need them. Doesn't the TRV handle the balance?



I plan to start out with 3/4 inch pipe on the return for the first two raidators and 3/4 pipe for the supply loop to the last two radiators. The rest of the loop is 1 inch.

Whizzer

Two Pipe System Design

Forgot one thing. I am planning to put a check valve in the return prior to the pressure activated valve.

LarryC

Why bother with the check valve?

Not being a heating professional, but why bother with the check valve?  Where is the reverse flow going to come from?  You did not list a second pump for a separate lower temperature loop or a water tank.



If you are doing all the plumbing in copper, would it make more sense to install two manifolds and do the runs in oxygen barrier PEX instead?  That way you can do flow balancing at the manifolds and easily isolate an emmitter if the need arives?

Mark Eatherton

Balance cock should not be necessary...

The TRVs will balance the system out.



Pipe size is based on connected loads. 3/4" is good for 40K btuH, 1" for 80K btuh and 1/2" good for 15K btuh, As loads drop off the supply main, main size decreases (to maintain air sweep velocity), and conversely, as the return main picks up returns, it increases in size, based on connected loads. You have to map it out to decide when and where these changes occur.



ME

Mark Eatherton

What Larry said...

Unless there is a possibility of natural thermo siphoning occurring, I would not worry about the check valve.



ME