Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Best Recirc Demand Control for Multifamily

Do you have a preferred demand control or energy conservation strategy for DHW recirculation in large (100 unit+) multifamily buildings?

I'm from a single family home energy auditing background, just starting to play with bigger multifamily buildings in NYC/NJ, serving as an Energy Consultant. :)

Amazed at what I believe is the pervasiveness of absurdly high recirculating loop temperatures, over-pumping, and an overall lack of demand controls or other energy conservation strategies within DHW recirculating loops. I mean....I can't see any reason for full pump capacity and 140F at the tap at 2pm in an Upper East Side, high rent building.

Any thoughts or suggestions would be much appreciated. As would a a new snow shovel, after mine broke moving 12" of the white stuff on OCTOBER 30TH!!!



  • Larry Weingarten
    Larry Weingarten Member Posts: 2,545
    edited November 2011
    I'm guessing...

    ... you might want to look at demand controls (www.gothotwater.com) with a return temperature of 105 degree, so people have shower water.  There are other approaches like distributed heaters or point of use rather than one central heater, or using tracer lines to keep the main line hot.... but I'd want to talk with Nehemiah Stone as he's been down this road for some time.  Here is a way to contact him; http://apartmentenergy-ieqretrofits.lbl.gov/people/tac/nehemiah-stone, or through Home Energy Pros. http://homeenergypros.lbl.gov/

    Yours,  Larry
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    edited February 2012

    I've landed in the exact situation as you, "Art".

    Only I have some experience owning and operating some 20 unit buildings, none of which had recirc.

    I'm looking at some larger buildings now, and they ALL have huge pumps running 24/7.

    I just started thinking about this today, but had a germ of an idea:

    1. Install a flow switch on the water heater cold supply. Then the existing big **** pump will crank on the instant hot water is called for anywhere in the building.

    2. Time how long the pumped hot water takes to reach the farthest fixture, and use a time delay relay to turn off the pump after that amount of time. A thermostat near the farthest fixture would prevent the pump restarting until the pipe temperature dropped to 110F.

    Of course, insulate the pipes. It's worth it because if someone showers within 1/2 hour of the previous shower, the water is still hot enough, and is therefore not wasted. Without insulation, the water gets cold in 10 minutes. (All estimates are very rough and depend on many variables.)


    Install a timer. But the poor guy who needs to shower at 4am would have to wait for his hot water. That would take a LONG time with these uninsulated 1-1/2" pipes. The above system would have no 4am shower problem.

    With the first scenario, the pump duty cycle would be cut down from 24/7 to maybe 10 minutes a day, saving at least $20/month.

    Any thoughts? ME, how to you see it done around here?
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • Pitfalls for demand controls?

    My understanding is that I am looking at a couple of prominent potential issues:

    1. Mechanical (Holby) mixing valves are not rated for varying flow rates. An electronic mixing valve, specified by the manufacturer for varying flow, is likely required.

    2. Recirculating pumps may have warranty issues if implementing a demand control strategy. Verify with the manufacturer the ability to vary flows at the pump.

    I'd love to hear any strategies that folks use with success....

  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    edited February 2012
    ME weighs in

    In a brief conversation with Mark Eatherton today, he said use a timer and an aquastat.

    But he is also apparently working on a better overall solution using a TRV, and Grundfos Alpha-style pumps. Can't wait to see it!
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    How its done around here....

    Same as it is done everywhere :-) WRONG...

    Most ALL of the DHW systems serving MFD buildings has experienced shortages of hot water at one point or another, and the brunt of the complaints falls upon the guys trying to maintain the systems. Their reaction is to TURN IT UP.

    Bless them Oh Lord, for they know not what they're doing.... They just want the phones to quit ringing and want people to get off their backs. So, in an effort to relieve the situation, they turn up the heat source, and eliminate ANY possible interruptions to the circulation/availability of hot water. This includes the aquastat that was applied to the DHW C.R. pump when the system was originally installed. If you so much as even LOOK at the aquastat, they threaten to cut your hand off.

    Many of the complaints stem from a lack of understanding, not only from the untrained maintenance techs, but also the service agent that is charged with repairing the boilers when they break.

    In the case of a side arm connected to a space heating boiler, there is typically an aqua stat connected to either the shell of the HXer or the outlet of the boiler, and it is typically set for 160 degrees F. The boiler is maintained at 180 24/7/365 for the DHW loads potential.

    This "mystery" aqua stat, which is intended to be a DHW priority control, is supposed to shunt the space heating pump during a period of maximum demand and simultaneous calls for heat. It typically gets rewired to control the DHW HXer supply pump. Doing so will cause a RoLlEr CoAsTeR ride of temperature at the points of use, resulting in complaints, causing the maintenance guy to, you guessed, TURN IT UP again... 200 degrees F boiler temperatures are the norm, aren't they?

    In some cases, a storage tank is thrown into the mix, which helps the fluctuations, and in some cases, alleviates the shortages, but if improperly piped up, it will actually EXTEND the shortages once they begin. This is usually due to not having a circulator (other than the DHWCR pump) to move water between the HXer and the tank. THis means it takes 40 minutes to recover the 119 gallon storage tank that Hank the plumber threw into the mix. (120/3 = 40)

    The other common infraction, due to the aqua stat being taken out of the picture by turning it ALL the way up, is that the check valve (if installed) is corroded open, so that when the aqua stat IS brought back into the picture, during a draw of hot water, the incoming cold water is allowed to charge through the C.R. system backwards, again causing a MAJOR fluctuation of hot water temperatures at the far end of the system, again resulting in phone ringing and name calling. Again, the maintenance guys, you guessed it, TURN IT UP, to 205 this time. Steam doesn't happen until 212 right??.

    As it pertains to mixing valves (which are SUPPOSED to be anti scald design), as the hot water is being recirculated through the system, if the water is too hot, the hot port of the valve is supposed to go closed, which diverts the circulation back into the cold port of the valve, thereby cooling it down, but keeping hot water moving through the loop.. Once cool enough, it closes the cold port, and diverts the flow back through the cold water inlet to the hot water source, forcing additional heat out of the tank and into the system. Set up correctly, they work like a champ. I am not aware of a normal Holby valve with flow limitations. It could be a misapplied valve, intended for a fixed flow.fixed mix operation (photo processing facility). MFD flow rates can vary from 1/2 GPM to 100 GPM in the blink of an eye.

    Another situation that I commonly see in the field has roots in poor design from the get go. Supply systems piped with a direct return parallel C.R. circuit, that causes people on the far ends of the system to have to wait for hot water. Typical response, turn the AQUA STAT ALL THE WAY UP. This is guaranteed to cause hydraulic erosion corrosion, and eventual supply and return piping failures. The plumbers response, as they are cutting out the old and putting in the new with Shark Bite fittings, "They don't make pipe like they use to...". You're right, they make it BETTER. These failures have NOTHING to do with the age of the pipe, but have EVERYTHING to do with the continuous, high flow rate around the DHW system. As Dan has always taught us, the solution is never in the same room as the problem...

    And then there are the TONS of cast iron pumps in potable water applications. (What do you mean we cant use cast iron pumps in these systems? The water mains are made out of cast iron, aren't they?" They MUST be bronze, or stainless steel.

    Rust never sleeps..

    As noted in another thread, I am working on a new design (new for potable water systems) that will balance out the flows in a poorly designed system, and keep hot water readily available at the furthest points of use, and consume ONLY the electricity necessary t get the job done. This will result in eliminating the ringing phone, back stabbing incidents, eliminate hydrolysis, significantly reduce thermal energy loss/consumption from the distribution piping, reduce cooling loads required to reject those stand by losses during the cooling season and cut electrical motor waste.

    I;d tell you more about the design, but I am in the process of working with a major pump manufacturer to come up with a total (patented) system design, and have decided to keep everything hush hush until savings can be confirmed and verified.

    At a minimum, the DHWCR pups in MFD and commercial buildings should have a timer and an aquastat to control the operation of the pump.Oh yeah, and a functional check valve and a means of being able to positively purge the C.R. circuit THROUGH the C.R. pump.

    Quite honestly, this is what I see all over this fine country of ours. People think and react the same everywhere.

    Stay tuned...

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    edited February 2012

    Gary Klein, the hot water guru,




    Wait a dang minute! They stole my idea from above, then went back in time and developed it!
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588

    Mark, point us to that "other thread"

    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
This discussion has been closed.