Thoughts on DHW circulation return controls for MFD settings...

Mark Eatherton

Wallies,



I am once again, involved with pre boiler/DHW system installation/replacements for multi family dwellings, and I keep coming across DHW re-cirulation return systems that are suffering from continuous run flat curved pumps, and the resultant burn out of the hot water mains and circ return lines. My normal methodology would be to incorporate an aquastat and timer into the control circuit for the DHWCR system, but who dictates the normal hours of pump operation? Many of the complexes have people working all three shifts, so there is no "typical" pattern of usage. Even with these controls, I believe that the previously worn out lines are still being subjected to erosive velocities, and the result hydraulic erosion corrosion and subsequent tubing failures.



My new train of thought, is to eliminate the timer, and incorporate a non electric thermostatic control valve on the return, and to utilize a DCECM bronze circulator to maintain flow through the system. If there are multiple branches on the return system, each branch would require a NETRV to control flow if hot water is present.



I'm thinking that this would result in minimal parasitic power consumption, lessen wear and tear, and eliminate water waste associated with purging tepid water from the mains.



I believe that Oventrop and others makes a NETRV set point control that can be used with a conventional valve, with the sensor strapped to the return lines.



Everything in modulation..... Including the DHW CR system.



Any of our Euro friends ever see this incorporated into larger commercial designs?



I know WILO makes a bronze version of the ECO DCECM circulator that would be compatible with the potable water...



What thinks ye?



Always looking for a better solution.



ME

meplumber

Just a thought in another direction ME.

A while back, I used a switch in the bathrooms to turn on the recirc pumps.  Simple but effective.  This was a MFD as well with everything from blue collar types (early risers) to college students (night owls) so I couldn't nail down a timer setting.  I decided to wire low voltage single pole switches on the wall near the sinks.  I used Taco SR controls to simply turn the bronze circs on and off.



This may not work for you.  I admit that it required some active participation from the tenants, but it extended the operating life of the circs and cut down on the need to run the recirc constantly.



Not sure if this helped.  Good Luck.

Jack

www.gothotwater.com

Mark, check this system out. It really is excellent. Give Larry at Metlund a call and let us know what you think of this. It is head and shoulders above any other system out there...imho that is!

Larry (from OSHA)

have you thought of this?

Hi Mark.  I've been using the small version for single family residential for a few years with good results.  (When it was Laing)  I did chop out the timer because it was a bit noisy and plugged it into an electronic timer.  Works great.  Low velocity so it shouldn't eat the pipes.



http://www.bellgossett.com/productPages/Parts-ecocirc-e3-Domestic-Hot-Water-Circulators.asp



Larry

Charlie from wmass

Thats what I was going to say Larry

I think domestic recirculating is a place where over pumping is far too common. If the circ return water was never warm enough to trip the aquastat yet it gets the water warm out to the fixtures would that not be good enough?

Mark Eatherton

Excellent idea meplumber....

But it has been my experience, that given an opportunity to have HID's (human interface devices) above and beyond a simple thermostat, that humans are subject to error. I'd rather not give them the opportunity to screw things up.



Now personally, in a SFD setting, I think it has good merit.



Thanks for the input.



ME

Mark Eatherton

Thanks Jack...

For an apartment complex, that would be a difficult and expensive means, especially in retrofit considerations. But thanks for the input.



ME

Mark Eatherton

Thats getting closer Larry...

DCECM is the right choice, now if we can get them to give us a constant pressure, variable speed option, then were cooking with gas AND electricity.



Thanks for the input.



ME

Jean-David Beyer

HIDs

I have friends who are incapable of understanding a simple thermostat. I cannot understand their thinking processes. I explain that if the house is colder than the setting, it will turn on the heat, and if it is hotter it will turn it off. They have 180F in their baseboard heat, and somewhat leaky house, so when the boiler goes off, it cools down in less than 1/2 hour, and when it goes on, it warms up within 15 minutes or so. They cannot deal with that. They might as well have an on-off switch instead of a thermostat because when they are cold, they turn it up a lot, and when they are hot, they turn it down a lot. So they have extreme temperature swings. When they go to work, they turn off their boiler with the red switch; they think this saves them money. I point out that if the temperature drops too much, they could freeze their pipes. They do not believe me.



Same with their air conditioner.



If they had recirculating domestic hot water, the only way that would work, other than always on, would be a motion detector that would turn it on as soon as they entered the bathroom or kitchen.



These are the people that will inherit my house when I die. If they turn the boiler off, no domestic hot water. If they try to do setback on my slab, they will not know what is the matter, and if they do not get a good contractor, ... . If they want it warmer that I have it set up for, they will not get it because the outdoor reset is pretty close to what it takes to get 69F inside. I do not really want to tell them how to diddle the reset curves. And dealing with the 12-hour lag between changing the water temperature to the radiant slab and getting a stable response will never ever get through to them. While I never want to be a heating contractor, I would never want people like them for a client even though I like them very much as people.



You professionals probably have to deal with this all the time. Patience of Job, if you ask me. I suppose I could learn the technical stuff from a book, and serve as apprentice for a few years for the practical stuff. But customer relations I doubt I could ever manage.

Ironman

A Very Simple Approach

Mark,



Buderus mod/cons come with a connection for the recirc that is factory set for 3 minutes on and 7 minutes off. Coupling an ECM circ with that might be a very simple and effective solution. I would think you could find a digital timer that would work they same way.