We deal in water every day when we deal with hydronic heating, but can there be too much water moving through the piping? Well, sometimes, and when that happens, the velocity noise can be unbearable. This becomes even more prevalent if zone valves are present.
I know many installation companies use zone valves, mainly due to cost, and if installed correctly they do a fine job. However, if they are not installed correctly, you and I are the ones who have to resolve the problem or the customer has to learn to live with the noise of water rushing through the piping.
Now, all zone valves are not created equal, as you can imagine. Taco and Honeywell are the ones I most found in the field, but there are other manufacturers coming out with their own versions. All of them have one thing in common—they all rate the valves in Cv ratings.
Did you ever take this rating into consideration when installing or replacing a zone valve? Are you asking yourself what is a Cv rating? O.K. well I just happened to pull this description from Wikipedia:
The flow coefficient of a device is a relative measure of its efficiency at allowing fluid flow. It describes the relationship between the pressure drop across an orifice, valve or other assembly and the corresponding flow rate.” Mathematically the flow coefficient can be expressed as: Cv = F √ SG/∆P where:
Cv = Flow coefficient or flow capacity rating of valve.
F = Rate of flow (US gallons per minute).
SG = Specific gravity of fluid (Water = 1).
ΔP = Pressure drop across valve (psi).
O.K., you got it now? If so, explain it to me! I found an easier explanation that makes sense to me and hopefully also to you. The flow coefficient or Cv is the volume (in U.S. gallons) of water at 60°F that will flow through a valve with a pressure drop of 1 psi across the valve per minute. O.K., makes sense.
Now we have a way to compare the amount of water that will flow through a zone valve or any valve or fitting for that matter. Go ahead and look for it on the paperwork that comes with each valve. Find it? Yep, it’s there. This rating now lets us know how much water will flow when only one zone valve is open, but it will also tell us how much water will flow when all the zone valves are open. It could make quite a difference in what circulator we choose to use, doesn’t it.
Imagine using a circulator pump on a system with four or possibly five zone valves? You need to size the circulator for the full flow of all the zone valves or you will not get heat to where you want it, right? What happens when one of those valves close and the flow increases by approximately five in each of the other zones? Now imagine only two zones or one zone is calling for heat. The whole reason for splitting the heating load into zones is what…. to only send heat to where it is needed, correct? So, it is not uncommon for this to happen. Imagine the amount of water designed for five zones going through one! What to do, what to do!
Well, the only true solution is to install a balancing valve. This is installed between the return and the supply piping and it allows the system to balance as the zone valves open or close. Instead of all the water going through the zone valve, the excess water volume now goes through the balancing valve and back into the heating supply or boiler.
This is not a new idea, but it is one that many technicians have not heard about or just forgot. If you want more information on this or any other hydronic problem, simply check with the manufacturer’s representative of the zone valve or check out the company’s website.
I have been in this industry for just over 42 years now and over the years I have learned a lot and forgot a lot. I hope you learned some things from me sharing my experiences with you over the past years. I have been thinking about retiring and doing more fishing, biking, or more traveling. I would like to hear from you and read your war stories, so e-mail me at firstname.lastname@example.org. So until we talk again, see ya.