Thursday, March 19, 2009

Geothermal - Part 3 (Concentric Fitting for Domestic Hot Water)

Most Geothermal heat pumps available today have the option of providing free hot water in the summer time. Although it sounds too good to be true, it really does work. Here's how: A geothermal heat pump cools your house in the summer by removing "heat" from the inside air and transferring that heat to the ground outside. Instead of transferring all of this excess heat to the ground, the heat pump can transfer some of this waste heat (about 10%) to your hot water heater. The only extra energy required to get this free heat is the electricity required to run a small pump (50 watts) to circulate water from your heat pump to the hot water tank. In this picture of one of our heat pumps, you can see four insulated lines - two large ones are for the underground loop and two small ones are for the hot water tank.

The system works best if you are willing to install two hot water tanks - one heated exclusively by the heat pump, and one heated by conventional means (gas or electric) for periods of high demand when your heat pump does not provide enough free hot water. In actuality, most installations probably use only one hot water tank for both purposes, with admirable, but not optimal, results.

Like everything else in our house, our hot water supply is set up a little bit differently. We have something called an indirect hot water heater, connected to our wood boiler. In the winter, the wood boiler heats the domestic water in this stainless steel tank via an integral heat exchanger. In the summer, the water will be heated by the heat pump. Downstream of the indirect hot water heater will be an on-demand heater to provide hot water in the spring, fall, and during periods of high demand. Typical hot water tanks have three ports on them... "cold in" "hot out" and "drain". So typical geothermal heat pump installations take advantage of the drain port to inject the "free" hot water into the tank. Our indirect hot water tank has no such 3rd port, so our installation required something custom-built. It's called a concentric fitting. (aka radial fitting)

The purpose of the fitting is to allow water to flow "in to" and "out of" the same port of the hot water tank. In fact, this was the original installation method employed by Water Furnace several years ago, until they came up with a more reliable method of using the drain port. I searched the internet for concentric or radial fittings, but came up empty handed, so I set out to build my own. I thought I'd post the pictures of it here in case anyone else needs to build their own some day. It turned out to be relatively simple. The ports on our hot water tank are 1" ports instead of the typical 3/4" ports, so my fitting will hopefully be more reliable than the original water furnace fittings, which (I'm told) had a tendency to clog up with mineral deposits.

The pictures should be self explanatory to anyone with the modest plumbing skills required to replicate one of these fittings. If not, post a question here and I'll answer questions if I am able.


Blogger Joost Bonsen said...

Hi Tom,

Lovely house!




March 19, 2009 at 10:24 PM  
Blogger oldmilwaukee said...


I love your blog. Just visited it for the first time and left a few comments. I'll drop in occasionally to stay in touch with the real world and the MIT world. :)

March 20, 2009 at 11:11 AM  
Anonymous Anonymous said...


Can you post a picture with this fitting installed and some labels of where water is coming and going? The output/input from the two valves is restricted somewhat and you're probably going to see a presure drop is this ok?


March 21, 2009 at 7:23 AM  
Blogger oldmilwaukee said...

A little more info about the last photo. From right to left...

*the first valve (called a boiler dran valve) is for draining the water tank.

*The 3/4" copper port (pointed up) is where the cold water supply will connect.

*The ball valve in the foreground (normally open) will supply cold water (from the tank or from the cold water supply) to the geothermal unit.

* The water from the geothermal unit (via a 1/2" pex line not shown) goes through the rearmost ball valve, and is injected into the middle of the bottom of the watertank via the long 1/2" copper line. (The appropriate length of this line would depend on what's inside of your water tank, longer = better) When the water comes out of this 1/2" copper line, it rises to the top of the tank through natural convection. This prevents the same water from returning to the geothermal unit.

Cold water can enter the water tank directly from the cold water supply via the threaded 1" port that you see. That's where the whole thing threads on to the water tank.

I'll try to post a picture when I get the thingamabob hooked to the water tank.

The valves with the green handles are called "full port ball valves" and they will not cause a pressure drop or flow restriction. Gate valves would haved caused a pressure drop (not a good thing), so I did not use gate valves.

March 22, 2009 at 11:04 AM  
Blogger Vladimir said...

Thank you for the explanation!

On a slightly different track, I really like what you're doing and wish you the best! My wife and I have similiar ambitions of leaving the corporate world for a simpler life. I don't think we'll go as far as building a timberframe home but we'd like a home in a private setting and are currently in the process of looking for an existing property in the country. I'm willing to take the longer commute but am wrestling with marketability of a secluded property as well as the potential tax burden given that we live in NY. Ideally we wouldn't have to rely on an employer and move anywhere we please.

Given that you have put in this much time and labor into the current property, are you concerned at all of potentially having to move? Are you planning to stay in KY no matter what life throws at you? In our case, we do not see our future in NY and are thus reluctant to invest on a larger scale. If we were absolutely certain that we would stay in a home for a decade or more, then we'd be willing to say yes and go.

From your postings, I can see that you’re putting in the absolute best (or close to it) in terms of technology, materials, and appliances into this home, that more likely than not you plan on retiring there.

God Bless,

March 23, 2009 at 6:19 PM  
Blogger oldmilwaukee said...


Yes, this is the house I plan to die in... I just hope I can finish it before then. Ha ha.

Seriously, I did set out to build the best house that I could, and it has become an obsession of sorts. My primary goals were: comfort for my family, low maintenance, and self sufficiency, but it turns out those goals can also be "green" I suppose.

I'd say build small (but solid) if you're not sure you're going to stay. If things work out and you end up retiring there, you can always add on or improve. Build a small part of your dream if you're not sure you'll be there long. I had to leave a bunch of blueberry plants and apple trees behind at our last house in NH. But I'm glad I planted them!

March 24, 2009 at 2:55 PM  
Anonymous Anonymous said...

Old Milwaukie where are you?
I need of fix of DIY timberframe from scratch!

I sure appreciate your blog!

Watching in the West

May 13, 2009 at 11:59 PM  
Blogger oldmilwaukee said...

I'm not dead, just distracted. I'll get back on this blog soon!!! :)

May 15, 2009 at 8:03 AM  
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June 8, 2009 at 10:23 PM  
Anonymous Anonymous said...

OK Thomas,

It's time to move away from the "Concentric Fitting for Domestic Hot Water" and post something new. Come on man give your far away kin and update!!!!!!

your favorite uncle,


June 11, 2009 at 9:17 AM  
Anonymous Russ and Carolyn said...

We're doing likewise:

Russ and Carolyn

August 14, 2009 at 12:47 PM  
Anonymous Steve said...

This comment has been removed by a blog administrator.

October 22, 2009 at 7:47 AM  
Anonymous John said...

This comment has been removed by a blog administrator.

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