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Outdoor Reset

Paul Rohrs
Paul Rohrs Member Posts: 357
The wheels have been moving slowly lately in my mind, but I am wondering about outdoor reset and constant flow. Joe at JalcoPlumb posted the other day with a constant flow system drawing using a tekmar 361. I pulled up the Tekmar 021 essay and one the first things it states is that the "Greatest comfort and efficiency is obtained when the supply water is constantly circulated through the system and the temperature of the water is adjusted to match the heating load". So if I design a system with outdoor reset and variable speed mixing, (or proportional mixing) without constant flow, while not inherently flawed, I am not designing for maximum comfort. I still have a comfortable and efficient system, and this is somewhat argumentative, but now I need to consider the parameters for constant flow. Can anyone tell me why to stay away from a constant flow in a given application. Domestic Hot water? Any secondary loop that is not going to pull BTU's from the primary is a candidate? I have seen a few posts with noise issues from Pex-Al-Pex supply lines that would be a good candidate as well. I want to re-define when designing to give the best package available, given a budget or guidelines. Is the criteria more broad in that I should use constant flow in a high water content, low mass boiler application when zoning by circulators? Does this exempt systems with zone valves?
Having said that, I am really looking forward to the new product from infinity labs that will give, "Indoor-reset". That might not be the right terminology but My skull full of mush hasn't sorted out the particulars of that control. I think I understand that it will monitor the Differential and modulate the boiler accordingly. We still need the availablity for mix temperatures, so should that be constant flow as well?

I love this industry and it's ability to keep me "trying to build a better mouse trap".



  • jalcoplumb
    jalcoplumb Member Posts: 3
    I am of the opinion....

    that in a well designed heating system that use of constant circulation can be a great benefit.

    In a new system I prefer to use one complete zone with constant circulation and outdoor reset. When paired with a boiler like a Munchkin the system will provide comfort and energy efficiency.

    I have been getting away from zoning, unless there is a mix of different types of heat i.e. copper-fin baseboard and cast-iron radiators. But then when I zone these applications I like to do it with two or three different constant circulation loops with injection on each. This creates two or three different reset systems that will provide comfort throughout all the zones.

    Doing a system in this manner tends to eliminate a lot of the short cycling you get from multi-zoned systems without a buffer tank. I see a lot of multi-zoned systems without a buffer tank that cycle on and off all day long. The boiler is sized for the whole load i.e. 130,000btu the zones are small 15,000btu zones. Throw in an indirect and wham cycle city.

    Just a few thoughts on the subject I could keep going but I do have to get to work.

  • shawn
    shawn Member Posts: 2
    constant circ systems

    Joe et. al.,
    Out of curiosity do you run into problems with internal gains effecting the indoor temperature. I have always been wary of constant circ do to internal gains an outdoor control can not adjust for. If for instance constant circ is maintaing 68deg indoor air temp and the customer has a party where 25 people attend, don't you get somewhat significant internal gains? The next question is if the VSI is maintaining 68deg and the customer is more comfortable at 70degs do you go back to the house to adjust the control? Lastly, do you run into problems where you are maintaining 68degs on the left side of the reset curve(starting parameters) and another temperature on the right side(design parameters) of the curve?
    I know Tekmar has a control with indoor temperature feedback. I am talking strictly outdoor temperature determining water temp. Also, what do you do to determine the desired water temp at design. Do you use software, experience or VooDoo Magic? It seems the comfort level delivered will be dictated by the accuracy of your heatloss.
  • hr
    hr Member Posts: 6,106
    I'm intrigued by

    the latest systems ME is doing. A constant circ loop with Oventrop dual sensor TRV at each zone. Theis would get you away from complicated micro processor challanges. Sounds so simple.

    Show it again Mark!

    hot rod

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  • Steve Ebels
    Steve Ebels Member Posts: 904
    My Holy Grail system of choice

    Uses the following parameters:

    Heat emitters are panel rads of some type or another utilizing a TRV in each room of the home. Large rooms get two circuits oriented on the east and west walls if possible so one side or the other will shut down when the sun hits it. A detailed heat loss of each room is mandatory for proper sizing of each rad.

    An indoor feedback sensor located centrally in the home to accomodate things like 20 people over for Thanksgiving dinner. (the turkey is thawing as I speak) This control will overide the outdoor reset curve programmed on the boiler control and modulate the water temp above or below the curve if needed.

    The boiler, oil or gas, must be able to operate in the 90-100 degree range, so, it has to either be designed for that or protected from low system operating temps by a mixing device of some sort. Much Much better to have a boiler that does not need a mixing valve. Modulating burner is so sweet to have also. The near boiler piping will incorporate a pressure bypass to protect the pump when all the TRV's are shut down. (rare but I like to design for worst case)

    Circulation is constant up to the adjustable WWSD temp.

    Domestic hot water production and recirculation is also handled by the boiler control with selectable priority.

    This system uses only 2 pumps, one for heat and one for dhw if the boiler is capable of handling low temps. (add another for recirc if used) No mixing valves, no injection ghost flow problems.

    Piping can't be simpler. run the heating circuit to a manifold(s) where all the PAP is terminated at. Use the ones with individual mini-ball valves on supply and return for easy purging of each loop. If you have to split the manifolds distance wise, use reverse return piping to balance them.

    The only option(s) would be heated bench, towel warmers, and maybe some radiant floor in whatever areas the homeowner wishes.

    Talk about economy of operation. One pump, system output matched to the loss at all times. Think cruuuuuuuuuise control.

    Individual room by room control of heat. "You want that back room at 50* Mrs. Jones? and your bedroom at 75*? Well that's just no problem at all" "We can do that!" Fast temp response to solar gain or sudden drop in temp. About a 10 minute flywheel effect.

    It all just adds up to comfort that is constant and perfectly matched to whatever the HO desires.

    I have yet to run into a customer that has not LOVED this system.

  • [Deleted User]
    Oventrop controls

    has a new device that senses room air temp AND return fluid temp. This basically gives you anticipation to avoid over shoot. In regards to the original post, you MUST have non electric TRV's at all points of control. Rarelly will you find two rooms with indentical room losses. If all rooms had the smae loss, your idea might work. Continuous circ with outdoor reset works wonderfully.

    The installation costs are substantially less because you're not home running all your piping, and there are no thermostats wires to run.

    The Euros have proven this system over the years. We're (as usual) late in catching on. Check out all the Oevntrop controls.


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  • jalcoplumb_3
    jalcoplumb_3 Member Posts: 5
    I was talking ....

    new system. I use software to do the heatloss. I would also use an indoor sensor.

    Yes, I do go back to get the temp. set. I show the home owner how to do it, but I will go back up to three times if needed. I find that in most cases after the second time we get the proper temp for the customer. It seems that I am setting the temp at around 65 to 68degs.

    I have one job that has a walk out basement with radiant in the slab. They have a large solar gain in one room due to direction. I notice that the constant circulation draws the heat from this area and distributes it throughout the rest of the slab part of wich is a garage.

    In a retrofit I take each job and evaluate the existing radiation, do a proper heat loss room by room, and evaluate each rooms heat loss vs existing radiation and go from there.

    Have a great evening/morning,

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  • Mark J Strawcutter
    Mark J Strawcutter Member Posts: 625
    how do you deal with

    setback? I see three options:

    1) don't do it since it doesn't really make a difference

    2) use an outdoor reset control that shifts the curve based on a time schedule. During setback, TRVs would open wide.

    3) use a conventional setback thermostat in some representative area of the home. During "occupied" times setpoint is overly high (like 90F) so reset curve controls system. During setback, thermostat controls system and TRVs would open wide.

    other strategies?

  • Chris Holley
    Chris Holley Member Posts: 4
    and don't forget mono-flo

    I have never really liked fin-tube..but fintube with TRV's on a constant circulation mono-flo system is really a whole different beast.

    I just finished up a retrofit with Tekmar reset underfit radiant on the first floor and unreset monoflow constant circulation TRV controlled fintube for second floor rooms. The TRV fintube rooms hold inside of a degree and are totally quite. No heat up start up noise. I oversized the fintube by about 30% to make for fast pickup when the trv's are turned up in normally vacant guest rooms.

    I just can't get over what a beautiful job those Danfoss TRV valves do on fintube. With the constant circulation they squeeze the output of the baseboard down to perfectly match the room's heat loss. With the baseboard only pumping out it's full output on design days, it seems like the air convection is greatly reduced making for a more radiant like comfort in those rooms. And best of all......no expansion noise from bang bang control.

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