Primary-secondary piping; outdoor reset


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Old 10-09-09, 03:42 PM
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Primary-secondary piping; outdoor reset

Hi all. I have a Peerless WBV-04 that I am about to install and am trying to figure out the piping/layout.

I have four zones of baseboard heat rated at 86k at 180 degrees. I currently have a domestic water coil but expect to install a Burnham 50 indirect water tank and a Modine 33 Unit heater for occasional use in a garage/shop. Heat loss is 70k. The Peerless WBV 04 boiler has three nozzle options: .95 with 102k BTU; 1.25 with 131k btu; and 1.50 with 156k btu. Current temperature set back at night and work days in the winter has all four zones activated and returning cold water to boiler.

Tekmar suggests piping the system with indirect water heater and hydronic unit on the primary loop, four way motorized mixing valve off of the close tees, with four zones of baseboard with zone valves, circulator pumps on primary, secondary, the indirect water heater line and the unit heater line, and with sensors on supply, return and secondary mixed. It seemed to make sense as I can run lower temperatures in the secondary loop and the mixing valve can protect the boiler from cool returning water causing condensation.

My questions:
1. Your suggested piping for system, including do I need close tees for the DHW and unit heater/garage zones off of the primary;
2. Where in system (primary/secondary/both?)do i put drain for bleeding air;
3. Do I need a balancing valve on return from baseboards on secondary?
2. Is there a better way to set up piping?
3.Is Tekmar the way to go with mixing valve, sensors and controllers, or are there other devices that are better?
4. Since the primary must be at least 130 degrees to avoid condensation, is it worth the fuel savings to set it up this way?

Thanks..I know this is a long thread!
 
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Old 10-10-09, 06:39 AM
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Current temperature set back at night and work days in the winter has all four zones activated and returning cold water to boiler.
Can you explain this a bit more?
 
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Old 10-10-09, 06:43 AM
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Tekmar suggests piping the system ...
Posting a link to the diagram you are looking at might be helpful.
 
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Old 10-10-09, 06:53 AM
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3. Do I need a balancing valve on return from baseboards on secondary?
2. Is there a better way to set up piping?
3.Is Tekmar the way to go with mixing valve, sensors and controllers, or are there other devices that are better?
4. Since the primary must be at least 130 degrees to avoid condensation, is it worth the fuel savings to set it up this way?
3a: I would think no, since they are zoned. As long as your pump is properly sized, flow won't be an issue.

2: maybe

3b: The mixing valve might be overkill... less complex is always better IMHO.

4: Remember that it's the RETURN water that needs to be above the dewpoint of the flue gases. That return water is always going to be cooler than the supply water obviously.
 
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Old 10-10-09, 11:21 AM
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For oil, you can go down to about 115F on the return temperature, assuming you get a decent firing time. (Broadly speaking, gas condenses at about 130; oil at 113.)

You could probably do just a straight bypass and provide adequate boiler protection down to a reasonable low-end reset temperature.

You could also go with something 'fancier' like variable speed injection.

4-way mixing is also 'fancy'. Both it and vs injection will require some thought about piping and control.

As to cost effectiveness, I would run some numbers on what kind of reset supply temperatures you'll need at temperatures where the house just begins to need heat, and on into the fall and spring. If you can do down to 80F for a lot of the shoulder seasons, it might be worth it in the long term. Otherwise, I'd see what others say here about how low you can reasonably go with a simple bypass.

Remember that with these fancier setups, another thing you really benefit from is comfort. The house temperatures are way more stable and it just plain feels better.

Check out the comfort-calc.net site for more info on piping strategies etc.
 
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Old 10-10-09, 10:02 PM
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Thanks for the replies.

If I do not use a mixing valve and go with a simple bypass, how would I be running the baseboard zones at a cooler temperature and how would i control the bypass for boiler protection (manually set valve?)?

The Tekmar piping diagram can be found at http://www.tekmarcontrols.com/listing/acrobat/a2071.pdf.

The temperature setback I was discussing was the thermostats calling for heat after the night setback and the cold water in the pipes returning to the boiler.
 
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Old 10-11-09, 08:02 AM
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That's one fancy (and expensive) system. Doesn't need to be. Simple bypass, if appropriate, would be manually set. Like a very good-quality globe valve.

What you're describing, particularly with the Modine, is a mixed temperature system. Looks like from your original post you recognize that. Relatively low for the baseboard, but high for the Modine. Don't have time to get my head around that, but browse the tekmar application guides and you should find a couple that are potentially a bit simpler.

One way might be to go with p/s and injection on the baseboard zones (or 4-way mixing), and treat the Modine and DHW as high temp loads off the primary loop. Use one control (362? Can't remember) for the baseboard zones and have the DHW and Modine call via a relay to fire the boiler to limit. Something like that.
 
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Old 10-12-09, 06:20 AM
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Xiphias, thanks for the response. I'm a little confused (or continue to be confused might be a more accurate statement).

The system that I am contemplating is expensive, about $700 for the controls and $500 for the motorized mixing valve, and I'd rather save the money, but want to set this up one time for long term efficient use.

If I do set it up as a simple bypass, is it correct to state that at best I will achieve partial reset as the return temps need to be sufficient to avoid condensation? With my boiler I thought the only way to get complete outdoor reset with the ability to run the baseboard loop at very low temperatures was to isolate the secondary loop with either a mixing valve or variable speed injection (The mixing valve seemed easier and if the control failed, I could operate it manually without the outdoor reset).

Regarding determining if partial reset is sufficient for my needs, I am on Long Island, NY with a design outdoor temperature of 12 and 5500 heating degree days.

If I set it up with bypass, how would you pipe it?

If I do set it up with mixing or injection, do you recommend the Tekmar controls, Taco controls, or some other set up? The Tekmar 362 is about the same price as the Tekmar 260 and 360, so that seems to be about break even.

Thanks for the help!!
 
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Old 10-12-09, 07:49 PM
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Paging rbeck.... I would defer to him or other more knowledgeable sort regarding how low you could push a simple bypass, but yes, you are interpreting correctly. Without complete isolation of primary and secondary you will be doing partial reset. Partial might be just fine, depending on your home's heat loss, type and amount of heat emitters, etc.
 
 

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