Hot water FAST

[Pat]

Wasn't sure if this belonged under water, indoor repairs or what...

I had previously installed a small (2 1/2 gal hot water heater in my mom's house since two of the bathrooms are over 60 ft from the hot water tank. It lasted well past the warrnanty (1 yr) but not long enough for me to consider it a bargain. I thought I would buy a 6 gal unit for only about $8 more but with a 6 year warranty. Unfortunately when I picked the crawl space access doors I picked them with only 12 inch vertical clearance and the 6 gal tank is a bit over 14 inches. I considered tearing one apart and reassembling it under the house but the tank is too big. SOOOO...

I'm installing a small bronze pump with plastic impeller. It takes well under an amp to run and moves 12-18 gal per min. Running the water to get it hot takes a looooong time with flow restricted faucets and showers and is wasteful. The pump will get 'er done in well under a minute. Here is a list of the major parts and pieces and a description of operation. Attachment is a wiring diagram.

The pump is installed so that it draws hot water from a hot water line and discharges it into the cold water line. Check valve keeps you from getting back flow. There are lots of ways to control a setup like this but I like this one.

The user (in either bathroom) pushes and releases a buton. The pump runs till the thermostat feels the hot water. The pump automatically shuts off when hot water arrives. You can't run the pump when the thermostat is satisfied, even if you hold the button down continuously.

Patrs list:
pump
check valve
momentary contact SPST switch (2 ea, one for each bathroom)
SPST thermostat normally closed, open on rise
120VAC relay with SPST normally open contacts
Indicator lights if you want to get fancy

Cost of the parts is approximately equal to the cost of a 6 gal 120VAC water heater. There is more installation labor than the heater would be. By insulating the pipes used for supply and return the energy losses are less than the standby losses of the 6 gal water heater so in the long run the pump will save a bit. It is definitely cheaper to run this pump than to run the well to get water to throw away while waiting for the "hot" to arrive at the bathroom.

[GaryM]

Pat,

we have the Metland system which works exactly as you describe. Ours is connected in the master bath. I stumble in and press the button. By the time I finsh "draining my tank", the hot water is ready to go. Takes about 40 seconds or so and no water goes down the drain.

On their website http://www.gothotwater.com/ there are several models described as well as alternate plumbing methods. We have the S-70 model.

[SLOBuds]

I thought these things were supposed to be run continuously. We are designing a new house, and will put some form of recirculation in it - just thought they ran more or less continuously (at very low volume).

Not so?

[GaryM]

SLOBuds,

If you look at this web page: http://www.gothotwater.com/D%27MAND/...ng_layouts.asp They show two different connection methods. The second method uses a dedicated return line and can run as you mentioned. They do point out that it can be expensive to run. Think of all that pipe radiating heat. Kind of like a hydronic heating system.

My system is hooked up as in the top diagram on the page. And I find myself quite satisfied.

[Chillimau]

My vote would be for a "well planned" as needed system rather than continuous. My MIL has a continuous system that when run continuous adds about 40-50 bucks to the natural gas bill. She is losing a lot of heat in the slab. When it is run for long periods part of the bathroom floor actually is radiantly heated, nice, but not the intended goal. She has put a timer on her pump so that it only runs around bath time in the morning. Still a pain if you are outside the planned time as off to the garage to manually turn on/off the pump. Pat and Gary have the "right stuff".

Gary

[GaryM]

I guess in the cold weather the heat's not wasted. But maybe the floor doesn't need to be too warm either. Electric heaters are expensive to run, but they are 100% efficient. At the point of use anyway! Generation losses and transmission losses are beyond your control.

With the Metlund system, or Pat's homebrew version, you need to make your connection at the end of the run. So that the hot water is available at the intermediary taps. Because of my house design, we did not supply the kitchen via the system. But the master and two guest baths are "in the loop".

[Pat]

All things considered, I'm installing two mechanical escapement style "twist timers" and leaving out the thermostat and all the other stuff. One timer in each master suite's bathroom. It is so cheap to run the pump for a few minutes it isn't worth any more complication. The timers are so no one forgets to turn the pump off. Both bathrooms get their hot water from the same central backbone hot water pipe so it only takes one pump. This is for my mom's house and is simple and straight forward.

Commercial installations like appartment buildings or motels and hotels may use continuous run systems but could usually save money with an intermittent system with a thermostat (there are case studies.)

It is GOOD to insulate the hot water lines whether or not you have recirc pump but it is more important with the recirc. Why people run the pipes under or through a slab without insulation escapes me. It is a BAD bargain. The insulation will pay for itself many times over.

Gary is right, standard electric water heaters are 100% efficient. Water heated via a heat pump is about 300% to 400% efficient, i.e. you get the same Btu for about 1/3 to 1/4 the electricity. In some places where the cost of a kiloWatt of electricity is quite high, folks buy water heaters with small heatpumps built on.

For our new house we have a flat plate heat exchanger to transfer heat from the hot water as it comes out of the heat pump on its way to the hydronic system. Couldn't find a cost effective hot water heater with a desuperheater coil so we used the heat exchanger instead. The ground sourced heat pump will heat the water in the water heater in the basement which acts as the "cold" water supply to a propane fired unit on the ground floor. I thought I had the recirc system all figured out but now I'm pretty sure I don't and have to rethink it. GRRRR!

The problem is that the heat pump as we have it set up for hydronic heat only makes about 120F water max. Not hot enough for DHW service. It will still be a boon to have the heat pump heat a storage tank of hot water to be used as "cold" water to go to the gas fired pump. It will be faster and cheaper for the gas fired unit to heat 115-120 degree water up to final temp than to start out with cold, 62F or lower water.

Definitely don't want continuous recirc here! The gas unit would end up heating ALL the water to its set temp, its contents plus the 60-80 gal in the basement tank.

In winter the heat pump will have to run a good portion of the time anyway so there will be lots of cheap (1/3 - 1/4 price) hot water. In summer the waste heat you are trying to get rid of with air conditioning heats the DHW, essentially free and only excess heat is thrown away. In the in between times when you aren't cooling or heating (not all much of the time, here) the gas fired water heater just does its regular job.

I'll have to ask the geothermal guru about the economics of runing the heatpump to make DHW when it otherwise wouldn't run for heating or cooling. Likewise I don't know the temp of the hot water produced when running the A/C but I think it is hotter than that produced for heating. This is a good thing as it lowers the cost of water heating even more.

It is no big thing but it would have been smarter to plumb the Jacuzzi tub to the tank heated by the heat pump. No reason to heat the water up a lot more than needed to just mix in cold water to cool it enough for use.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[DocHeb]

</font><blockquote><font class="small">In reply to:</font><hr />
All things considered, I'm installing two mechanical escapement style "twist timers" and leaving out the thermostat and all the other stuff. One timer in each master suite's bathroom. It is so cheap to run the pump for a few minutes it isn't worth any more complication. The timers are so no one forgets to turn the pump off.

[/ QUOTE ]

Rather than a timer, could you use an infared detector (like floodlights have) to turn the pump on whenever somebody walks into the bathroom? It could run for a while and then shut itself off. They make detectors to fit into a single gang box.

[GaryM]

</font><blockquote><font class="small">In reply to:</font><hr />
Rather than a timer, could you use an infared detector (like floodlights have) to turn the pump on whenever somebody walks into the bathroom?

[/ QUOTE ]

That setup is available for the Metlund system. It's recommended for commercial installations like public restrooms. http://www.gothotwater.com/cart/scri...?idCategory=16

[Pat]

DocHeb, As you gathered from Gary's response it is a GOOD idea in some cases. Note however, that the innexpensive motion detector light controller that replaces a toggle switch say for a closet light or whatever ISN"T DESIGNED TO SWITCH AN INDUCTIVE LOAD.

Pumps look like a big inductance (coil of wire with a magnetizable core) to the switch. Inductances cause BIG SPARKS (voltage and current surges) when they are connected or disconnected. The circuitry in the light controller will likely be damaged by the inductive load.

If you read the fine print it will likely NOT be listed for use with fluorescent lights. Magnetic ballasts for the fluorescent lamps are an inductive load. Recently a few controllers, rated for fluorescents, have hit the big box stores but I'm not too sure I'd want to try one to control a pump motor. Specialty circuits good with inductive loads typically cost much more.

Also, since the walk in closets of the two master suites in my mom's house are accessed from a door inside each bathroom, you'd be pumping water every time you went to the closet, whether you needed to or not.

Since the time to get hot water is way under a minute with the pump (about 15-20 seconds) you can just give the timer a twist when you enter the room for any reason ultimately requiring hot water and it should be there by the time you need it.

I will likely buy at least one of the "package" units like Gary has for our house under construction. My hot water distribution and recirculation plans for the new house are in a state of flux, having made a DUMB decision that I had to rescind. Yet another small design flaw or otherwise known as a wrinkle in the fabric of space-time.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]