ECN Forum Forums General Topics of the Trade General Discussion Area Zone valves....

hal,as far as i know the boiler starts on outside air temp and return water temp.

I'm not going to get into a long dialog with you but around here in the north east boilers are either maintained temperature or cold start. Most are the latter to save energy and will only run when a thermostat calls for heat and will cycle on the high limit aquastat until the thermostats are satisfied. There are some high end boilers and controllers that will modulate the water temperature based on the outside temperature but most operate the same way.

Not all valves have spring return, some have 24v at the valve all the time and use a signal provided through a electronic controller or t-stat to tell the valve which way to go.

Sure and there are DDC (direct digital control)systems and networked systems with (GASP!) CAT5 wiring also but that't not what the original post is about now is it.

r is one side of 24v w is for heating and i have never heard of t&t. i think you may be the one with bad info. i highly doubt that a end switch on a valve is going to start the boiler, unless maybe the boiler is in florida where they dont need heat.

The end switches control the boiler the same way as a low voltage thermostat would with only one zone.

-Hal

Don't worry Trevman, it is easy to forget that different ares use different equipment.

In this area I have not seen any residential zone valves that use either 0- 10 v or 4 -20 ma. The ones used here are crude full open or full closed valves using 24 volts.

Welcome to the Forum.

Bob

I think Hal gave a more detailed explanation of what I was describing. I differ a little with him in that I think you usually just start moving fluids with the switches on the zone valves. I'm used to seeing the boiler doing its own thing, running between its low and high temperature set points. Thermal mass, delta Ts, flow rates, # of zones calling for heat, all that good stuff, will eventually cause the boiler to kick in at its low temperature setpoint.

I should've mentioned that we're talking low voltage, current limited here. The switches tend to connect to a module that contains its own 24 volt transformer and the relay/contactor that controls the circulating pump.

Any air handlers/heat exchangers at the far end might well have their own high and low temperature set points (or just 1 set point with a dead band or differential.) This way, you don't start blowing cold air around or stop the fan while the coils are still hot.
Joe

Trevman's description reminds me of only one system that I've dealt with. This Transportation Office had only one loop to heat the whole building. A heat exchanger in the back used modutrols to control recirc. and make-up air dampers. These modutrols have pots in them that reference the wiper to the vane position. Another Modutrol, on the water side, controls a proportional valve to control how much water goes through the heating coils Vs. around them, before going to the rest of the loop. This valve also has position feedback via a pot in its Modutrol.
I doubt that this is what's in Attic's basement.
Joe

In this area I have not seen any residential zone valves that use either 0- 10 v or 4 -20 ma.

They are modulating zone valves uses with a building control system usually in a commercial application. They may be open, closed or anything in between depending on what the controller wants. Instead of a switch there is a potentiometer that gives position feedback to the controller- 4 to 20ma loop current depending on the position.

-Hal

is this how a residetial boiler with a fan works? t stat calls for heat, valve opens ,end switch makes&starts boiler& pump,high limit senses coil is hot and starts the fan. also would there be a seperate coil in the duct for each zone and therefore a limit or temp sensor at each coil to start the fan? Is this what the attic rat is talking about?

Hal thanks but I am aware of 0- 10 v or 4 -20 ma controls.

I just have never seen those systems used for standard residential zone valves.

Bob

is this how a residetial boiler with a fan works?...

There can be differences but with most hydro-air systems the stat calls for heat, the zone valve opens starting the circulator and boiler. The fan can start at the same time or it can be controlled by an aquastat on the return water line from the coil. When it gets hot it turns the fan on. This just keeps the fan from blowing cold air until the coil heats up.

also would there be a seperate coil in the duct for each zone and therefore a limit or temp sensor at each coil to start the fan?

There is a separate fan coil (air handler) unit for each zone with it's own associated ducting. Like I said, the fan can be started as soon as the stat calls for heat or they can use an aquastat on the water line.

I have seen systems that are further zoned with dampers in the ducts and a controller that interfaces the T stats and dampers then operates the zone valve as above.

Keep in mind also that each air handler usually has an air conditioning coil also so it is used for both heating and AC. This further complicates the fan control and the way it is wired to the T stat.

I should add that the T stat is wired to the air handler which in turn controls the zone valve and outdoor AC unit, except when additional dampers are used.

-Hal

[This message has been edited by hbiss (edited 12-03-2005).]

Russ,
These valves usually come with a mnfrs. data sheet giving the options for various circuit control layouts, with wire colors to stepper motor and relay feeds and outputs shown.
Usually, the valve is opened by a signal from a programmer, time clock, switch or programmable thermostat. Upon being fully open, a relay in the valve closes, ( and often there is a NC set of contacts available too), which gives an independant signal which you can use to fire up a boiler or furnace, run water circulators etc.. This independance of signal is vital if you have multiple zone heating or domestic hot-water heating + central heating etc, because you don't want to backfeed other programmers or thermostats upstream.
I have used this sequence;
Programmer signal to valve, and to the water circulator. That's safe, the water is circulating when the valve is open. Relevant valve relay signal taken to the boiler [furnace] firing sequence through a thermostat, so when the boiler/furnace shuts down, [ie. satisfied], the circulator continues to run using residual heat.
I know this sounds obvious, but in complex set-ups, make a sketch of the circuit showing the wire colors and identifying the valves etc., and keep it for reference. You'll be back to fit replacements in the future.
And if an old dolt like me can do it, anyone can!

Alan

do you mean each zone has its own fan and its own set of coils or would there be just one fan and possibly damper controls?