Zone Valves and Weil-McLain Ultra boiler

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Old 01-27-12, 07:35 PM
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Question Zone Valves and Weil-McLain Ultra boiler

Currently I only have one heating zone and one DHW zone. I am thinking about adding a Hydronic Unit Heater for the basement workshop area. Something like this but that's a different topic: HC-33L-01 - Modine HC-33L-01 - HC33L01 Hydronic Unit Heater - 29,500 BTU

I was going to just add another loop with zone valves but boiler manual has me confused. It shows three call for heat contact locations. One is currently the DHW aqua-stat and the other is the thermistor. When using zone valves it indicates to connect the end switch in the place of the thermostat, or use a relay if its a 3 wire type zone valve.
Here is the manual check out pages 79 and 80:
ug3_boiler_manual.pdf

I see two issues with this.
1. What happens during post purge? The zone valves are going to close and the pump will continue to run.
2. The exact same problem occurs during the automatic circulator exercising. Its only 10 seconds so maybe not a big deal.

Am I missing something here?
Ive figured out away around it but it seems kind of backward and hardly worth it just to use post purge. I'd put 120Vac relays on the cirulator outputs to turn on the zone valves and then put a 24V relay on the end switches to run the pumps.
 
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Old 01-27-12, 08:16 PM
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What zone valve do you have? I would think from your post you have a 4 wire with end switch correct?

Looks like up to three zones can be wired to that control. 15 1-6 on the controller.

You should have a circ for the DHW. Your install should look like fig 48.

Post purge option sends the heat to the DHW I believe and not the heat loop. Like I said the DHW should not have a zone valve. I believe you will have flow issues if you do. The boiler circ is not meant for that use.

The circ excersise is just for off season really. Has nothing to do with if a zone is open or not I believe. Just keeps the pump moving during the summer, and it would only be the heat loop pump anyway. The DHW and boiler pump will be working in the summer.

.

Mike NJ
 
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Old 01-27-12, 08:56 PM
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I didn't get the zone valves yet. Currently the system is set up as figure 5 on page 12 except there is only one heating zone so no zone valves. I am looking to add the zone valves along with the second zone as pictured in figure 5.

The way post purge runs on this boiler is it just keeps the same circulators running for an adjustable amount of time after the thermostat shuts off. I guess I can just tun off post purge for the heat zones. Not really sure it has much value added.
 
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Old 01-27-12, 09:35 PM
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Yes fig 48 is high head/flow rate. sorry.

Yes fig 5 is your current piping without the zone valves?

I would leave the post purge at factory settings. Moves water after shutdown to prevent hot spots on the exchanger from soak time after burner is off. I would guess. The max is 4 minutes.

DHW pump is set 30 seconds DHW pump only on DHW call.

Boiler and sytem pump set for 30 seconds after heat call ends.

Mike NJ
 
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Old 01-27-12, 09:57 PM
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Just realized something. I dont have the bypass pressure regulator. Item 25 in figure 5, I dont exactly have a high head pump its a taco 007 which is max 10 ft of head, so I never bothered to install it. I guess if I install that then I could allow the pumps to run after heat call ends and the zone valves close. Honestly it seems like that kind of defeats the purpose of the post purge. I wonder if I could install it in such a way that it would only bypass the basement heater zone valve. I dont mind dumping the extra heat from post purge into the basement. I just dont want it bypassing during normal operation when the other zone is calling for heat. Seems like it could be tricky to set.
 
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Old 01-28-12, 07:19 AM
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I think the post purge is only to evenly move the heated water through the boiler after the burner shuts down to even the heat. It would be good with your one zone with out zone valves. I would probably set it for the full 4 minutes.

But what pump actuallty runs? Is it just the boiler pump?

Also how many BTU of element on the zone now? Possibly you can add to the aready existing loop. Use a moniflow tee sytem. Possibly use a thermostatic valve for the basement heat. Of course the unstairs zone will need to call for heat to get heat in the basement.

Plus you are low temp with that boiler. That 29k btu heater is at 180f no? At 130f or so temps the btu will be reduced.

Mike NJ
 
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Old 01-28-12, 07:45 AM
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When using zone valves with a single speed pump you should always use a differential bypass valve (DPBV) to balance the flow between zones as zone valves open and close. The DPBV will do the opposite of the zone valves. As zones start to close the DPBV starts to open to bypass water around. When all zones are open very little water passes around the DPBV. When all but one zone is closed or all are closed and pump post purge water will flow back to the boiler.
The purpose of the post purge is to move water through the boiler to avoid hitting limit due to residual temperature build-up in the boiler and hitting limit. With the use of todays low water volume boilers it is more critical to properly pipe with the use of zone valves and DPBV's. Cast iron was a little more forgiving to improper application of zone valves.
Taco-Hvac: Differential Bypass Valve
 
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