Free Hot Water?

DCRC · Sep 8, 2004

Has anyone seen this system before?

It's a simple idea. A system that uses the heat from your air conditioning systems freon to assist your hot water tank.

http://www.trevormartincorp.com/hru.asp

check it out and let me know what you think.

Since we run are A/C 9-10 months out of the year it sounds like a neat idea.

GRUMPA · Sep 8, 2004

That is curious indeed, if theres water touching the condenser coil it will eat thru it in time. I wish they had some sort of diagram as to the mechanics behind it. Living where you do solar I would think would work better, theres 2 types open and closed loop systems. Closed loop are pricier and have more parts. Open loop uses the solar to pre-heat the water before it goes into the water heater and is alot cheaper.

In this house I had the condenser in a pool of water eliminating the condenser motor altogether. Worked like a champ for 5 years (lower bills much colder air). Then the water ate right thru the metal and I just went back to the original design.

Birdhunter1 · Sep 8, 2004

Grumpa, the water doesn't exactly touch the coil as I thin you described or are thinking. What it does is the water (for hot water generation) is run through a tube that is wrapped around the discharge line of the compressor, heat is transferred from freon-copper tube-copper tube-water. It's kind of hard to explain without a picture but it works real well. I use to be a sheetmetal worker and the company I worked for for several years installed a lot of geothermal equipment and this was standard on all of our stuff. It is very neat and you would wonder if it worked well enough to justify it. One house in particular that we did the electrician ran the wire to the hot water heater and left it hanging for the plumber to hook up, the plumber didn't hook it up because he thought the electrician would do it. We had hooked up the hot water generation to our unit and it was like this for 4 months. we went back to pressurize the loop and I noticed it and the plumber happened to be there hooking up a sink in the basement bathroom so we discussed it. The homeowner happened to be there and we asked him if his hot water ever ran out. He said (with two teenage girsl and a wife) he was the last to get in the shower every morning and about halfway through it ran out. He just thoguth it was because of the woman factor, we hooked it up for him and he never noticed it runnig out again and never noticed his bill being any different from then on. For 4 months the only thing heating his hot water was his a/c unit.

MicroPilot · Sep 8, 2004

I have a geotherm unit in my house and have the water heater turned all the way down. Never have a problem running out of hot water.

A buddy of mine is an HVAC installer for one of the bigger local contractors, and was telling me about this demo they had recently showing this new thing for using the heat from the AC to help the water heater. I said, "Wow, just like my geotherm unit has been doing for years."

BTW, this is only supposed work in the summertime when running the AC, but I don't change the temp setting of the water heater in the winter and don't really notice any difference in amount or temp of the hot water.

SPIKER · Sep 8, 2004

I under stand what you are saying I THINK: you have the AC cooling loop of copper/aluminum coils, for the HOT freon, and then a COLD water copper/aluminum tube is attached to the freon tube side by side. the cold water circulates through one tube and into the hot water tank. the hot AC freon actually pre-heats the cold water into WARM/hot water before the water gets to the tank correct?

this would probably work well in WARM places, but up here it gets way cold, you need water lines burried 4' deep many cases to stay below frost line... anything attached to a non-functioning AC would mean it is setting outside in the ice cold temps... it probably would be OK as long as you had a SUMMER/WINTER setup and drtained the coldwater line after the summer heat was over... WE only used AC a few days this year, so it would be worthless as far as re-capturing MUCH from the install date to the tear out date.

for you southe & west boys though it sounds like a plan...

MarkM /forums/images/graemlins/smile.gif

boustany · Sep 8, 2004

I don't doubt that there would be a savings, but (to put it mildly) the company's hot water savings are a tad optimistic.

Lets say you want to heat 40 gallons of water by 60 degrees F (from 50 F to 110 F) in one hour (their first hot water example). That takes 6.4 KWhr. (KW = Liters x Temperature Rise (°C) / 790 x Heat-up Time (hrs.) ), or $0.64 @ $0.10/KWh. x 365 = $233.60 vs their 'savings' of $299 (upper right hand table) for a family of 2.

So they claim to save more than the cost to heat the water (I wonder where the money comes out?). In fact, if you look closely, the table on the left is the cost of heating the water and their calculation supposes you save all of it with this magic gizmo. (They seem to ignore the operating costs of the heat exchanger, which is cute as well).

I would be surprised if they could save more than 10% of the heating cost by preheating the water a few degrees. The A/C savings is immaterial, and probably overstated as well.

It sounds very suspicios to me. /forums/images/graemlins/mad.gif

I'd ask for an independant engineer's report and a guarantee. That usually scares 'em away.

BIGUN · Sep 8, 2004

Remember the difference in A/C load between Canada and somewhere like say south Texas is like night and day.

I remember reading in a Popular Science type magazines a few years back about this revolutionary new type of A/C developed by some guy up north. He was so proud of it and said the only time it wouldn’t work is if the temp got over 90 deg F or when the humidity exceeded 80%. This is laughable to anyone living in Houston or anywhere around that area where it exceeds both of those figures almost every day during the summer.

Where this may not be practical in Canada, it might make all kinds of hot water in Texas.
I heard Dan Rather who used to live there, say Houston is a city that runs on Freon. No way I would live there without A/C or with it for that matter. /forums/images/graemlins/ooo.gif

Birdhunter1 · Sep 9, 2004

SPIKER and Micro: The hot water generation (HWG) will always work on your geothermal unit whether it is heating or cooling. Your HWG tubing is wrapped around the discharge line of the compressor which no matter if heating or cooling will always be hot. With a geothermal unit the outside temp is irrelevant for the most part, what matters is how well your house is sealed up. Since the ground stays the same temp all year (40-50 depedning on geographical location) and your house thermostat setting is probably close to the same the whole year the unit actually never notices any big temp swings. In fact the only swing is what your house is set at. So, if your house is sealed and insulated well and doesn't loose or gain a lot of heat then your unit runs less, since the unit doesn't operate in temp extremes and is almost at a constant operating temp it doesn't really change as far as cost to operate. What should be figured is cost to heat/cool the space which is considered by how well the house is insulated/sealed and how muchit looses or gains heat. I hope this may help.

Boustany: Not to argue the ratings they showed but: hot water generation is a waste product when running a geotheraml unit in A/C mode. In the part of this post above and my earlier post I explained that it comes from teh discharge heat of the compressor, that heat needs to be expeled somewhere so heating your hot water is simply trasfereing a waste product into something useful. Therfore Iwould look at it and say I am wanting to cool my house, I can cool my house but i have to get rid of the heat somehwere. I need to heat my water, how abuot getting rid of my heat from cooling myhouse and making a way for it to heat my hot water. The only cost involved this way is the cost to cool my house. (Actually you also have to run a small pump that circulates water from the hot water tank to the unit and back. It doesn't even draw 1/2 amp on 110 volts ac). Basicly heatig your hot water in the summer time by use of your a/c system is free because your running your ac unit anyway. Now it will also owrk on a geothermal unit in heating mode, but you are slightly robbing yourself of some heat by requiring more to heat your hot water but: the basic principle of a heat pump is it is cheaper to transfer heat than it is it generate heat. A good example is a heat pump vs. straight electric furnace, both systems run off electricity which is cheaper? A: the heat pump. Okay with this beig said would it be cheaper to transfer heat to heat your hot water or generate it electrically. You are robbing your system slightly but it still has plenty enough heat that is being transferred making it cheaper than anything else to do the same.

if all of you guys want more information i have the link below for the geothermal equipment distributor we use to deal with when I was working for the sheetmetal contractor. When i worked there we had Climatemaster equip. and they have since gone with Geo-Comfort. I have o first hand knowledge of Geo-Comfort stuff but the service tech at the shop I use to work says they are nice. The link is to Enertech Inc. http://www.enertechinc.com/

MarkV · Sep 9, 2004

Birdhunter, Geothermal systems depend on an exchange loop to transfer ground temperature to a heat pump. From what I have read the most common type of exchange loop is buried poly piping. I have also heard of systems that use two drilled wells to draw from one and discharge into the other. The third system I have heard of is an exchange loop of poly pipe that is laid in a body of water like the pond in my back yard. Have you ever worked on a system that was setup in water? Or, have you ever heard of any comparisons of the different types of loops?

MarkV

Birdhunter1 · Sep 9, 2004

Correct, they do require an exchange loop but there are actually four types that could be used. The piping used is polybutylene pipe and it is all fusion welded. One type of loop system draws water from a source then discharges it to a source (drawing from a lake and returning it to the lake). I have never dealt with this type. The other three I have dealt with. One is a ground loop that is installed horizontally, one pipe is buried at say 5' the other underneath it at 8'. I don't prefer them becuase it takes a large area (roughly 500' of pipe one way per ton of refrigeration required) and the ground temp will change slightly at these depths. The good thing is they are cheaper to install than the vertical loops. The pond loop requires a given average depth and must cove so large of a surface area. There have actually been instances of the loops not being sunk far enough or the pond not being deep enough and it will literally be a block of ice in the winter. That is why I would shy away from a pond loop. Don't get me wrong they do work, one house we put a geo system in was right at the edge of an old strip mine and the pit was used as a pond with a pond loop, but not every pond is going to be as deep as a strip pit. The fourth type is the vertical loop which is in my opinion the best. The vertical loop is pipping gooing stright down in the ground, usually about 150' per ton of refrigeration is what is used thoughit can be veried for say a 3 1/2 ton system they may drill three 180' loops where a 3 ton system would be 3 150' loops. What I like about the vertical loop is that the ground temp NEVER chagnes at the depths this thing reaches so to the unit it is never seeing a change in the water returning to it whereas the pond loop, open discharge and the horizontal ground loop you will see changes. Another thing about the vert. loop is that it doesn't take up as much space and you'll be less likely to dig it up or it be in the way of new projects. Another nice thing is that when they are drilling if they hit water and run the loop through that water (water will be surrounding the closed loop) you get an AWESOME heat exchange.