Hot Water Recirculation Pump Usage
daen
| Posted in Energy, Heating & Insulation on
We moved into a home built 10 years ago and it is equipped with a hot water recirculation loop. The feature is really nice since there is virtually no waiting at the tap or shower. Here in the desert, water comsumption is an issue.
However, the pump is plugged directly into an outlet and runs 24/7. Can anyone help me quantify how much energy usage is associated with this? My climate is Phoenix, AZ.
A friend has a similar setup and put his pump on a timer. It runs for a few minutes on 10-minute intervals and only during the family “awake” hours. Sounds simple enough to set up but I would like to compare the cost of the timer versus how much to run the pump and heating losses in the loop.
Thanks, Daen
Replies
A better setup is a thermostat, installed at the cool water return point, or, better, at the furthest point of usage. This turns the pump off when hot water is detected.
(Is your water heater gas or electric?)
The water heater is electric.
A thermostat at the points of usage would be "undesirable" to wire back to the pump. The thermostat at the return point is a nice idea.
There is a recric system that uses under sink valves to control the recirc pump which will save you the most. The pump only runs when you demand hot water. Its works by sensing the water temp when you open the hot water tap. When the temp is too cold it will shut off the water saving the waste and turn on the recirc pump until the temp reachs the desired level. The water is diverted into the cold water system so that none is wasted. It doesn't provide you instant hot water but it does adress water waste and it eliminates wasteful pump time when water isn't being demanded. Remember too that anytime the pump is running and hot water is not being used, you are cooling the water which results in the need to reheat the water another waste you don't have in the above system and in your case the heat that is lost from the hot water is being put into your home where your air condition is working to remove it. There are some that don't even have a pump and just depend on normal water pressure to recirc until the temp at the point of use hits the desired level. In a bath you can put the valvle on the sink. You then start the hot water on the sink and when it hits the right temp and starts getting hot water, you turn on your shower negating the need for a valve on every fixture.
In short, what you have right now is the absolute worst of all worlds. You are running a pump constantly to provide for sporadic use. You are cooling your hot water causing the need to heat it again and you are heating your house causing the need to cool it again.
A timed pump improves this but still has many of the above negatives.
Hot water
The idea is that you have instant hot water -whenever you want it at any point. Its a nice idea - you consider the benefits and the costs.
I find that fitting a really good thick pipe insulation works for me. The water comes out quite warm (not hot) Where I save is on the heat loss, the pipe doesn't have to be heated every time by the water running through. And the already warm water is easy to use.
I suppose the questions are, how long is the pipe run? How much heat is lost from the hot water left in the pipe? And if you run the water off - how much is wasted?
Does the heat from the pipe add to the ambiance of the home, or is it lost under the floor? (or where ever) Do you use/save the run off?
Hot water
Probably, a pipe stat, fitted close to the boiler on the return leg - will do.
$$/year
A fractional horsepower circulator will cost on the order of about $50/year to operate 24/7.
What I found with my hot water circ loop is that the pump is unnecessary. Gravity (unless you have a single-story slab on grade house) will provide all the motive forece required. The elevation diference between the basement and the first floor is enough to drive the minimal flow necessary to keep the line warm.
The issue isn't the cost of running the pump, it's the cost of heating the water. A constantly-running recirc system is essentially a hot water heating system, and when the heat is coming from electric resistance heaters that's an expensive way to heat the house (and even more expensive if you're running the AC at the same time).
(Good to see the ad for "Hot
(Good to see the ad for "Hot Water Heaters" just to the left of this thread. Still don't know what you're supposed to do if you want to heat cold water, though.)
Thanks for all the additional comments.
For my situation, I am looking for a simple approach. So as a simple retrofit the timer or thermostat at the pump get the "thumbs up" for now. Anyone have a brand specific thermostat to suggest?
Thanks, Daen
My FIL lives west of Phoenix. In their bathrooms there's a button that starts up the recirculation pump. The pump runs until the water at the pump gets up to something like 90°.
So you have to wait a few seconds, but it sounds like that system would use a lot less energy.
Hot Water Recirculation Pump Usage
I found a pump system for under $200 that installs at the farthest fixture and senses temperature, called "Chilipepper CP2011 Hot Water Demand Pump", that looks like it could solve your problem.
Jim
"
Yeah, that name is a take-off on the Taco brand, which has long offered similar pumps.