Hot Water Recirculator Efficiency Concerns


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Old 05-04-06, 02:24 AM
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Exclamation Hot Water Recirculator Efficiency Concerns

I recently installed a comfort series instant hot water recirculator that uses a pump at the water heater and a comfort valve installed at my farthest sink from the water heater. I performed the test in the manual to make sure the comfort valve was functioning correctly. The test was simple, shut-off the cold water supply valve under the sink then turn on the cold water faucet above the sink. This allowed water from the hot water pipe to come out of the cold water faucet until warmish water reached the comfort valve and eventually closed the valve.

This test showed that the comfort valve stays open until warm water reaches the valve to close it. Which got me to thinking, shouldn't this valve always be closed unless the pump on the water heater turns on like when I want hot water during select times of the day? Otherwise, water from the hot water line might enter into my cold water line whenever the water in the hot water line was not hot enough to close the comfort valve. The last thing I wanted was a slow draw of hot water coming from my water heater. Keeping hot water in the hot water line all the time just to keep the valve closed was not an option I could afford.

I had to know if water would be drawn from my water heater when I didn't need hot water but just cold water. After house of thinking how I could test my concerns I unplugged electric cord from the pump on the water heater and waited for the water in the hot water line to get cold. I then went outside and turned on my sprinkler system to water the grass cause I knew only cold water would be used. After ten minutes I went to the sink where the comfort valve was installed and opened the hot water faucet to see if there was still cold water in the hot water line. I couldn't believe it, the water was very warm. Water apparently had passed through the valve and into my cold water line.

Am I doing something wrong? Had I installed something incorrectly? I sure don't want water from my water heater watering my grass. Any suggestions? I checked all the connections and re-checked that the recirculation pump actually "was not" plugged into an outlet. HELP!
 
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Old 05-04-06, 04:26 AM
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If, while watering your lawn, did you check the temperature of the water coming out of the sprinkler? The hot water valve at the sink should be warm, meaning the pump is doing its job. As soon as hot water hits the valve it ceases to circulate hot water through the cold water pipes.
If you had cold water watering your lawn and hot water at the faucet, then all is well with the world. If hot water came out the sprinkler, then we need to investigate further.
 
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Old 05-04-06, 03:05 PM
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As stated earlier in the initial message I purposefully unplugged the power to the pump to check/test/validate my theory that:

When the comfort valve "is open" (there is no hot water in the hot water line) and someone uses cold water in the home, will water from the hot water heater flow up to the comfort valve and close it while the cold water which used to be in the hot water line passes through the valve and add itself to the cold water which is coming out the faucet.

Because if water from the hot water line enters into the cold water line when I only open the cold water faucet to brush my teeth, this would mean that my water heater is gonna start up unnecessarily and raise my energy bill.

I assume that is why the water in the hot water line warmed up when I watered the grass. No noticeable warm water was detected at the sprinklers.
 
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Old 05-04-06, 04:19 PM
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OK, it is the job of the recirculation system to keep hot water at the hot water tap. So if you are moving water, either cold or hot, some cooling will take place in the pipes. The recirculator will come on and possibly cause the water heater to come on, but not likely every time you use cold water. But it will come on only when the water at the hot water faucet where the sensor is installed calls for it. I am not a big fan of the recirculator. I had a customer, who, when they had high gas bills, turned off the recirculator, and the gas bill dropped dramatically, since the water heater wasn't having to work to keep the water hot on the 3rd floor even when they were away.
 
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Old 05-04-06, 09:11 PM
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No worries mate. When you brush your teeth, you should not get any flow of hot water. ( Note that the water in the cold pipe will be warm IF the pump has been running, but it will quicly use that warm water and be all cold.). If you could measure the spot pressure on a hot water pipe and a cold water pipe, cold will be higher slightly due to pressure drop across a load I the water heater). Similar idea to IR drop in an electric circuit. SO, if there were to be cross flow, it would be cold water back into the hot line. This actually happens if you turn on the shower valve and use a shut-off button on the shower head. A check valve inside the comfort valve prevents this from happening.

The reason the prescribed test works is because you have ZERO pressure at the cold water tap under the sink ( you closed that valve) so when you open the cold tap, there is a path of least resistance thru the comfort valve and out the tap. Open the cold valve under the sink, and flow will stop thru the comfort valve.

In normal system operation, the pump overcomes the pressure differntial I mentioned. And you will have the side effect, as in any retrofit recirc, that the cold piping will contain hot water for several seconds when the cold tap is first used.
 
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Old 05-05-06, 12:21 AM
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Let try this one more time.

CONDITION #1: Comfort Series Pump mounted on water heater is unplugged or in a scheduled off time period

CONDITION #2: Water in hot water line is cold

CONDITION #3: Comfort Valve is OPEN (because water in the hot water line is cold)

CONDITION #4: Cold water faucet opens (or other cold water tap in home)

CONDITION #5: Water pressure in cold water line drops (due to the open faucet preventing pressure to build up in the line)

CONDITION #6: Pressure of water in hot water line is higher then pressure in cold water line because no faucet is open on hot water line

When the above conditions are all true, what prevents the cold water thats been sitting in the hot water line to pass through the comfort valve?

The comfort valve is open...so the valve is not going to prevent crossover

The higher pressure in the hot water line easily overpowers the lower pressured water in the cold water line...so that won't prevent crossover

So, as far as I can tell, when the pump is scheduled not to run and the water in the hot water line has cooled, causing the comfort valve to open, if I use cold water from anywhere in the home causing the cold water lines water pressure to drop lower then the pressure of the water in the hot water line, then water from the hot water line will bleed over into the cold water line and continue to do so until hot water from the water heater eventually reaches the comfort valve causing it to close.

My concern, doesn't this mean that I'll be drawing / wasting heated water from the water heater when ever a family member opens the cold water faucet to brush their teeth, flush toilet, water the lawn, etc?
 
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Old 05-05-06, 04:26 AM
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No. It seems as if you are trying to second guess, diagnose, improve upon, or otherwise question the use of a unit that has been proven to work. With that said, the recirculation pump does just that. It recirculates cold water back to the water heater until the hot water reaches the sensor and tells the unit "I'm hot". Now you have hot water instantly, or within reason. The differences in pressure in each water line are inconsequential to the valve.
In normal operation there will always be hot water against the sensor, and the valve will be closed. Now, if you unplug the unit, it will close and prevent cross over. When you initially plug it in, if you turn on a faucet, you will get water from the unit, since it hasn't had time to recirculate and do its job, yet. But as soon as the hot water gets to the valve, it will close, and any warm water you experience will be miniscule. From this point, if you leave it alone it will work on its own without human intervention.
 
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Old 05-05-06, 02:03 PM
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The pump which is mounted on the hot water heater has a timer. We set the timer to operate the pump between 6am to 8am for morning showers and 8pm to 10pm for evening showers. We've limited ourselves to these periods because we don't want the added expense of always having hot water in our homes hot water lines...that would be very expensive.

At twelve o'clock I filled 3 glasses of water from my hot water faucet and measured the temperature of the water in the 3rd glass. The temperature of the water was 70 F in all three glasses.

I then opened the "cold water faucet" and let it run for 2 minutes then turned off the cold water faucet.

I again filled those same three glasses with water "from my hot water faucet" and measured the temperature of the water in the 3rd glass. The water temperature was 88 F

How did the water in the hot water line go from 70 F to 88 F when all I did was open the "cold water" faucet for 2 minutes?
 
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Old 05-22-06, 10:54 AM
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I finally found the solution to the mystery. Here's the link

http://www.redytemp.com/Bypass_valve.jpg
 
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Old 05-23-06, 09:41 PM
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Opening a cold faucet does not create a state where the hot water pressure is greater than the cold. Both hot & cold water get pressure from the same water main. That is, the hot water gets it's pressure from cold water pressure going into the water heater.

What may be happening is that the check valve in the unit isn't working 100%, or is slow to close (there may even be some debris in it). Water should not pass through the unit at the fixture after the water is hot, although enough will pass through to close it (but you tested that with the cold angle stop turned off). That warm water in the cold side may stay warm for a while; you may not be waiting long enough for the warm water to cool.

The best folks to ask abut this would be Grundfos. Their # in Fresno is: 559-292-8000. Or go to the Grundfos website & click on 'contact us'.
 
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Old 05-24-06, 06:49 AM
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I would agree with the pressure argument. It just seems like a poor design to allow the valve to open in a scheduled off period. It does seem to be a pretty inefficient system. I'm currently looking at providing hot water to a distance bathroom. I was thinking of going with the push button recirculator system.
 
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Old 05-24-06, 10:21 AM
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There are a few recirculation systems available and as far as I know, they all work. But far & away the best system would be run a line from the furthest fixture back to the water heater, with a pump & aquastat & timer & check-valve & appropriate valving. I would make a good effort to do it this way before resorting to other methods.

What I'll often do is put in everything except the pump - if I think that the system will recirculate by convection. The valves will make it easy to install a pump later on if it doesn't convect, but so far they all have worked.
 
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Old 05-24-06, 06:58 PM
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My concerns were never about the warmish water in the cold water line, it was about the phenomenon of why water from inside the hot water line was able to pass through the comfort valve and into my cold water line even when the pump was not scheduled to run, whenever I used only cold water. When my family brushes teeth or flushes toilet the last thing I want is any water from my hot water line to pass through the open valve to assist with cold water use. This is double duty on my water heater plain and simple.

I have since ordered the redytemp instant hot water circulation system. They claim not to have the bleedover phenomenon because they use a solenoid valve that only allows water to enter the cold water line when the pump actually runs. If their claims really are true, I should notice colder water from my cold faucets and less duty on my hot water heater. I'll comment after I experience it.
 
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Old 08-28-06, 07:31 AM
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Smile

It's been two months now with my new Redytemp. The wife and I were impressed with it's professional look and at how quiet it runs. We both agree the Redytemp is way better then the other one we had. Its easy to tell the difference between the two especially from the cold water faucets. We couldn't get nearly as cold a water when we had that black plastic valved system. Being able to set the temperature of the water we want is our favorit feature. Our water bills have gone down around 20% and I'll never forget the wifes suprize that the gas bill hadn't gone up but down 10 or 15 dollars. Of course we do use the timer so it doesn't run constantly.

The ivideo on their website makes the installation look easier then it was but thats probably just from not being used to crawling under sinks everyday. I'm sure that girl had some practice runs before she got filmed doing the install standing up..

I just took a brake and asked the wife if she thinks the price difference was worth it. HECK yes was her response, but she didn't us the work heck, I won't repeat the word she did use. I have to agree it is definately the better system and if it last past the two year warranty I'll get another for my inlaws. I look forward to having it in the upcoming colder months.
 
 

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