How to prevent check valve malfunction in a hydro-air system?
WEG
| Posted in Mechanicals on
I have a propane water heater with a loop to the air handler. Potable water goes through the coil. I noticed that my water heater would run twice an hour even though there was no demand. I guess I should have cleaned the back yard up before June. Anyway, I found the coil was not so apparently there was a convection loop happening. I closed the valve and all is well. My plumber says that since I have potable water running through the coil, I will always have this problem. Is that right? Should i stick some type of solenoid valve in the loop?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Walter,
Hydro-air systems can be tricky to troubleshoot. Here is a link to a very useful document that you should probably read: Combo Space / Water Heating Systems—“Duo Diligence”.
That article notes, "Combo systems must have a check valve that prevents thermosiphoning of tank water when the space conditioning system is in the cooling mode. This thermosiphoning can occur when water in the heat exchanger loop is cooled during air conditioning; the cooled water falls to the tank and is replaced by rising heated water, that cools, etc. (Both water heating and air conditioning costs go up when this happens). Trouble is, this valve is really prone to jamming from contaminants—flux, soldering debris, pipe tailings, etc.—during installation. The entire system must be completely and thoroughly flushed
as part of the installation, a surprisingly difficult detail to impress upon many technicians."
A simple heat trap may just be the answer also . When water is heated it becomes less dense than cooler water and naturally wants to rise and since you have a big circular loop it will act like a ferris wheel and the hot water will rise while the cooler water returns to the tank , been happening that way for eons , nothing you can do to change the physics . Fortunately you can combat this by directing the supply piping to the air handler downward as soon as it leaves the tank and before it goes to the coil . This simple way works and eliminates one more mechanical part that can require changing or can malfunction for several reasons . Check valves can become stuck , collect debris , scale up , need to be changed . Employment of an ECM circulator that optimizes flow rates dependent on heat taken out of the coil is also a real good idea , it will optimize the efficiency of the heater and use between 9 and 42 watts , Taco Bumble Bee , since you will be addressing this issue anyway it is a good opportunity for this upgrade , it also has an integral check valve . Have your plumber or heating contractor determine head loss and required flow rate for your situation and see if the Bumble Bee is adequate , if not there is also the 008 VDT which will save less than a BB but still will make the coil and water heater operate more efficiently and will not effect wire to water efficiency adversely . .Hope this helps .