Contols: Tekmar 260 outdoor reset for mixed temperature system

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Old 04-21-11, 09:22 PM
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Contols: Tekmar 260 outdoor reset for mixed temperature system

I am looking to run outdoor reset on a mixed temperature system with a bypass and and I'm trying to wrap my mind around setting up the controls.

There are four zones of heat (with one circulator and four zone valves, one zone DHW (with a circulator), and one zone with a unit heater (with a circulator) in a part time shop, which when in use, needs 180 to 200 degree full temp heat to satisfy the demand. I want to run the four zones of heat with outdoor reset, but have the DHW and unit heater getting full temp operation. I am looking at the Tekmar 260. The two high temp zones come off the supply side on the boiler side of the bypass. The low temp zones come off the supply side on the system side of the bypass.

I know I can run DHW to the Tekmar 260. How should I run the unit heater?

I was thinking of running an R845A switching relay back to ZC on the triple aquastat ( L8124A)to fire up to high limit for the unit heater and have the unit heater circuit get around the Tekmar 260. Will this work?

Another possible option is to run both DHW and unit heater demand to the Tekmar 260 DHW demand connection, and have the DHW and unit heater demands and the Tekmar 260 output go through switching relays.

Does the Tekmar 260 DHW circuit fire the boiler to high limit, or does it keep it to a temperature to satisfy the internal temp requirements of DHW (about 140 degrees)? If it doesn't fire to high limit, then my second plan will not work.

Any suggestions? Thanks in advance for the assistance.
 
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Old 04-22-11, 04:18 PM
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i have a tekmar in my house but i dont need a secondary high output loop so im not sure exactly how you can work this without having some type of secondary heater for your shop area. I think the DHW priority fires boiler until demand is satisfied. Why dont you eliminate the shop area loop and put in a gas garage heater. do you have gas?
 
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Old 04-22-11, 06:54 PM
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The 260 does run 180F for the DHW.

I think you may want to hook both the DHW and the unit heater up to the DHW side of the 260 and run them both on priority. I think if you hook them up to the DHW side of the 260 and use a relay to put the DHW on priority and not have the unit heater on priority, it wouldn't give you what you want. In that situation, if another zone calls for heat, that zone will get 180F water when you are trying to run it at lower temps based on the outdoor temp.

Although, you may want to run the the 260 with DHW priority and have the relay setup for priority of the DHW over the unit space heater. That would make sure your DHW has the fastest recover time.

Hope this wasn't too confusing.
 
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Old 04-22-11, 06:56 PM
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The 260 over-rides the OD temp setpoint on the boiler, it will go to high limit.

The unit heater in your shop... why not let it run with the same temp water as the rest of the heating zones? When the rest of the home can run on somewhat cooler water, why do you think the shop heater can't?

Remember this too... unless you have a CONDENSING boiler system, you can't do a full boiler reset with the 260. Your lowest operating temp should probably not be allowed to go much below say 140-150 ...

What boiler are you running, and are you burning gas or oil?
 
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Old 04-22-11, 06:58 PM
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Do you think a system reset would be better suited for him?
 
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Old 04-23-11, 07:23 AM
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Thanks for the posts.

The boiler is an oil fired Peerless WBV 04, and with the bypass I will at best achieve partial reset. The DHW is an Alliance 50. The unit heater is a modine 47.

I know I can run the whole system on reset temperatures but that does not work for me. I oversized the unit heater so that I could fire it to 180-200 and heat the space when it is needed without too much time from cold to satisfying demand (I dont want to waste money heating the space when not in use). When it is cold out it takes time to get the space up to working temperature, if I ran it on reset colder temps it would take much longer to satisfy demand. I want to be able to leave the space cold and when needed, satisfy demand quickly so I can get to work. That is why I am trying to run it full temp and go around the outdoor reset with controls.

RSSTEAM, that's a good idea, and I thought about it when I laid out the system, but the system is installed and in use at this point, so I am committed to the plan. I am running one boiler to satisfy all heat and hot water systems.

Any comments on the viability of my using a switching relay back to the triple aquastat to get around the 260?

NJ Trooper, given that my unit is not condensing, do you see value in running the outdoor reset at all? I could just leave well enough alone and run the system as is with the current controls.

Another option is to set it up primary secondary, and I plumbed the near boiler piping with close tees (that are currently pluged) to do that, but with the additional pumps and controls, I was not seeing the savings. Any comments?
 
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Old 04-23-11, 03:54 PM
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If you want that unit heater to heat the space quickly only the times when you need it, I would definitely hook it up via the DHW priority.
 
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Old 04-25-11, 05:37 AM
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Use a tekmar control that has a setpoint demand to it.
This will boost you water thump to the desired set point, ie 160 180, but will keep your heating zones active as well. Just make sure you have some form of mixing device present to prevent too much hot water from entering your heating zone if you have infloor or other tyoes that can be damaged by too hot of water.
 
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