Interesting (to me) plots with hot water, recirculated

J

Jack Arnott

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Jan 29, 2011
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So our power bills have been higher than expected. We had our HVAC person in yesterday to try and fix a problem with some windows (on motors) that won't stay open, and one thing we looked at was recirculating hot water, or hot water on demand. I asked the engineer about it when the plumber and contractor suggested it, and he thought that with the water going through insulated joists, that there shouldn't be much concern. The photo is of a few day history of the DHW (top and bottom of the tank), and the GSHP (ground source heat pump), with both the load and source shown. The GSHP has been kicking in when we take a shower, but this heats the water to about 100-110, the last bit is topped off by a coil in the tank. Towards the end of yesterday you can see where we turned off the recirculating pump. The gist is that we have been spending not only a lot of energy on the system to keep hot water always available at any sink or shower, but also, it has been re-heated exclusively by the coil. Which is a double whammy, because the coil is 100% efficient, but the GSHP is running at about 450% efficiency. Since we are quite early in our power bill cycle, we should see a big dip in the next bill.
 

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Re: Interesting (to me) plots with hot water, recirculated

I assume you're talking about a pump that circulates water around a circuit which connects all the taps and then back to the hotwater storage tank? If you are then put a timer on the pump so it runs during the periods of most demand ie just before you get up then maybe in the evening that way you'll save some money and still get the benefit of the "instant" hot water. Alternativly put a pipe stat on the return leg after the last tap though this can be a pest to retro fit. G
 
Re: Interesting (to me) plots with hot water, recirculated

gordon mcgregor said:
I assume you're talking about a pump that circulates water around a circuit which connects all the taps and then back to the hotwater storage tank? If you are then put a timer on the pump so it runs during the periods of most demand ie just before you get up then maybe in the evening that way you'll save some money and still get the benefit of the "instant" hot water. Alternativly put a pipe stat on the return leg after the last tap though this can be a pest to retro fit. G
Click to expand...

Or motion detectors in the bath rooms/usage points that would trigger the circulation pump to run. Ideally cutting the pump off once it's up to temperature would save energy too.
 
Re: Interesting (to me) plots with hot water, recirculated

Hi guys, yeah, I have the option of either installing a timer on the wall, and have it control the pump, or taking the head off the pump, and buying a more intricate pump with more timer options. Or switching it with the motion detectors, (which are already installed).

The problem with the motion sensors is that the bathroom in the basement gets used mostly for a restroom, and not a shower, and it is in the next room from the water heater, so very close, and the bathroom on the main floor is also our laundry room, and utility room, so it gets a lot of traffic that is not related to either bathroom/shower. (We already disconnected the HRV from the motion sensor for this reason, and have it on a switch to operate manually.)

Basically after two days we are not missing the hot water being immediately available feature. The old house had a very small footprint, and no big deal. While this is much bigger, it is still not that expansive, and we were talked into this feature by the contractor/plumber. We are waiting only a couple seconds more for the shower, and not having it right away in the kitchen is just not that big of a deal. Even then, it's only about 40'/13M.

I will do an update when I see how much money we are saving.

Regards, Jack
 
Re: Interesting (to me) plots with hot water, recirculated

In my world of being a heating engineer I vaguely remember there being a suggestion that the maximum amount of water that should be drawn off before it got hot was 2 litres, this was over 35 years ago though so things may have changed since then. G
 
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