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Approaches to multiple heating zone control for hydronic (hot water) heating systems:
Heating zone circulator pumps versus heating zone valves: which approach is better for controlling multiple heating zones in buildings?
This article series describes how to diagnose & fix circulator pump problems on hot water or hydronic heating systems.
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Heating circulator pumps or "zone circulators" are used to force hot water from the heating boiler through radianting devices such as hot water baseboards or radiators. The circulator is switched on as needed or in some designs may be wired to run continuously.
[Click to enlarge any image]
Here we discuss the alternative methods of multiple heating zone control, choosing between using individual heating zone controls typically all serviced by a single circulator pump and controlling zones with zone valves (photo at left) and using individual circulator pumps, one for each zone.
Each approach has its advantages and dis-advantages. I remain unconvinced that either approach is always the "only" right answer to the heating needs of a building
Our photo at left illustrates the use of multiple zone control valves to manage multiple heating zones in a building.
Arguing whether multiple circulator pumps (photo below) or multiple zone valves is a better approach to heating zone control is like arguing religion. Some heating contractors prefer using individual circulator pumps, one per zone, perhaps because they recall the history of unreliable zone valves which tended to clog or jam in some models by some manufacturers.
The "zone valve" gang retort that modern heating zone valves are as reliable or more reliable than [some models of] heating circulator pumps and that a zone valve costs a lot less. And adding zone control to an existing heating system may be less costly by adding a zone valve than by adding a circulator pump.
The fans of heating zone valves argue that the valves are easier to install, less expensive, and require less maintenance than individual circulator pumps. You'll read below that not everyone agrees with this view.
Those less enchanted by zone valves argue that zone valves jam, stick, don't work reliably and are thus annoying. In my experience, older zone valves that I encountered in the 1970's and 1980's were often a budget model that did not perform well and were not long lasting. But modern zone valves have in my experienced proven reliable and easy to repair.
The disenchanted also point to pumping capacity or flow rates possible with multiple circulators or variable speed circulators, and the use of circulators to operate the separate heating "zone" used
Even when multiple circulators are in use to control heating zones in a building it may be easier to use a zone control valve if you decide to split a heating zone into two separate loops or control areas.
Details about how zone valves are installed, wired, and when needed diagnosed and repaired or replaced are given in a separate article found
Question: reader comments on multiple circulators vs. multiple zone valves for heating zone control
(Aug 17, 2012) Barney said:
I have tried both multi pumps and motorised valves and I would like to make a few points.
Firstly, the cost of modern 60-30 or 50-30 pumps are not that much more costly than the more popular motorised valves. When you consider the failure rate of the seemingly most popular Honeywell and their copies (normally cheaper)motorised valves the multi-pump approach is probably cheaper.
This is because of the Honeywell type design which depends on a synchronous motor running to hold the valve open and eventually the synchronous motor fails. They are not teribly expensive but a hastle to change and if you can't do it yourself it costs a plumber/heating man.
There are better designs such as the Satchwell but are still very expensive. I use Grundfos pumps and in particular the Alpha 2 model.
[Image at left, Grundfos alpha series variable speed circulator pump - Click to enlarge]
Another point, many heating engineers are full of s--t in saying you have to use a larger pump on large systems. I have talked to Grunfos technical people and as long as the pump is able to meet the water volume load the smaller pumps are fine.
I use the Alpha 2 rather than the Alpha 2L pump becaause of the display showing the Load being taken in Watts. My circuits are running at between 9 and 12 watts which over a period of time represents considerable savings in electricity over the lower cost and more older 35 watt cheaper traditional model.
A couple more points to answer some of the comments made and questions.
No, you do not have to use a relay as most if not all 230 volt thermostats can cope with the small current requirements including startup currents of most modern pums like the Alpha 2.
Anonymous is wondering about water backing up into the other zones. I wondered also and installed at the end of each loop a non-return valve. Very simple device and very cheap from BES in the U.K. Hope this helps somebody!
How do we control hot water flow when using multiple circulator pumps?
July 3, 2012) Anonymous said:
When using pumps for zoning,what stops the water from enterning the other zones
Anon: the flow-control valve, a check valve usually found at the boiler hot water riser pipe(s), prevents water from circulating through zone piping until the circulator for that zone begins to spin - causing a more significant pressure difference across the zone.
[Click to enlarge any image]
See CHECK VALVES, HEATING SYSTEM for details about flow control valves.
Question: adding zone valves and sub-zones on a hot water heat system
(July 16, 2012) kenny said:
if i decide to add a zone valve to my boiler do i have to hook it up to the relay on the boiler
In this installation a thermostat operates the zone valve on a call for heat, causing the zone valve to open to allow hot water to flow thorugh that zone piping loop. Then the zone valve's end-switch that closes to turn on the circulator relay.
Kenny - as you'll see in the wiring instructions for your zone valve, the thermostat causes a low voltage motor in the zone valve to OPEN the valve so that hot water can flow into the zone. When the valve is fully open, an "end switch" in turn talks to the circulator relay to tell it to start the boiler's circulator pump.
Continue reading at MULTIPLE CIRCULATORS HOW TO HOOK UP or select a topic from the More Reading links shown below.
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