Controling temperature in radiant zones

Tom Hopkins

Hi everyone,

We have a hydronic system with several problems. I have include the schematics of the present configuration and the modifications that we want to make. Please let me know of your thoughts, comments?


1) The hydronic system has three radiant zones as shown in the attached HYDRONIC.JPEG schematics.

The three radiant zones are supplied by one mixing valve. Each zone has a pump. We get temperatures of 135F when the pumps are OFF and the mixing valve closed. Even when the pumps are running, it is impossible to control the motorized 3 way valve to get accurate water temperatures in the radiant zones. It seems that the water returning to the boilers is entering the radiant zones by their returns. Would a simple check valve, as shown in HYDRONIC MODIFICATION.JPEG schematics (revision cloud 8), installed on the radiant return solve the problem?


2) The boilers are also used to heat the domestic hot water and there is no bypass for the D.H.W. priority load. With the present system in HYDRONIC.JPEG, we are running the water through the water/glycol exchanger even when there is no space heating demand.

Would a bypass at the water/glycol heat exchanger with a 3 way motorized mixing valve, like in HYDRONIC MODIFICATION.JPEG(revision cloud 9), solve this problem? We have a PLC that controls the system and it could also control the motorized valve.


3) There is no air separator or chemical treatment on the system to protect from the corrosion of the tubing. Would an air/dirt separator installed after the boilers, as in the HYDRONIC MODIFICATION.JPEG(revison cloud 10), be appropriate ?


If you have any other comments it would be apppreciated?

Thanks all,
Luc