We took the mini plunge

I have one, and it worked great...till it plugged up. So if you install one, insure you have a water softener or water that will not have the minerals plate out on the inner heating coils.

 

It's that damn Florida water! I wonder why you couldn't use a glycol system with a heat exchanger to prevent plugging up the water passages? Might solve that problem.

Icarus

 

If I got the right utility provider the rates actually looked pretty reasonable, about 8 cents/kWh...but I had a lot of trouble looking it up so it might be wrong.

Your heating degree days there should be about 20-25% more than mine as best I can tell and that will cost fuel. Of course summer will be easier for you and that should help your electric considerably. (Your cooling degree days show to be half that of mine.)

My understanding is that at the peak temps a well-sized AC unit should be running nearly continuously and holding set point. That was counterintuitive to me originally, but the reasoning is that this allows more uniform temperature management with the smallest possible system. Start up cycles are less efficient. If the unit rarely runs because of too much extra capacity the room gets stuffy, then too chilly when the unit cycles.

Plug them into a "Kill-a-watt" meter and you can get an idea of what they are using in the winter.

No doubt about that. I've been known to remove one light bulb at a time in problem areas until my kids get the message..."if you don't turn out the lights when you are out of the room there won't be any lights in the room." CFL's saved a fortune when the kids were tiny and wanted full lighting from a closet and bathroom at night. Fortunately, they are weaned off of this now.

Showers can be an issue on water heating/water consumption with the kids. Home Depot gave out some little 5 minute "hour glass" timers that stuck to the shower wall and the kids loved them, probably because it was a visual indicator/game that they had direct feedback and control over...sort of like the MFD in the Prius. Knocked over 500 gallons/month off of their water use (probably half of that was hot water.)

 

Main problem is likely that when you add an intermediate fluid you introduce another temperature approach restriction and you have to circulate an additional fluid as well. And it won't eliminate plugging if you have the same amount of heat transfer to the water, since the water will get just as warm and therefore be just as prone to precipitation on the exchange surface. (On the plus side, liquid heat transfer coefficients are high and temperature crosses are easier to manage in countercurrent operation.)

With the retrograde solubility (precipitation as temp rises) of calcium in water, plugging can be a real problem. Our well water was incredibly hard where I grew up, so much so that I literally scooped out limestone from the water heater in the house and barn several times per year trying to keep them running. Still the elements failed frequently.

One thing I picked up from working with plate and frame's briefly in fouling services: high shear worked well in preventing scaling. It seemed counterintuitive to use tight clearances and smaller packs but the relatively high local velocities kept the surfaces clean. More plates meant lower velocity and a self-fulfilling prophecy of fouling. Higher velocity also reduced wall temp at the fouling surface, again reducing fouling tendency.

 

Shawn,

You're right that you will add another layer of complication by adding a second transfer medium, but the complications are (IMHO) outweighed by the fundamental efficiency of the system. As for the system plugging,,, the percipitating out of minerals due to the heat, would take place in the large exchange tank rather than in the small pores of the radiator.

It would seem that you could design a system with a sacrificial loop that could be easily serviced or changed in the event of too much scale build up.

I confess it is beyond my engineering experience however!

Icarus

 

Just a short history of how laziness saved my rear.
1) Original Water Softener in house breaks. After repeated attempts to fix, I gave up and threw unit away.
2) Original Air Conditioner rusts away. Get new unit and have ECU installed. Works great. Allows me to turn off water heater circuit breaker for 7 months of the year (till rest of family complains about the water heater being broke sometime in Oct. My clue to flip circuit breaker back on....secretly.)
3) After 3 years ECU clogs. Have not fixed yet (good move!)
4) Get Kinetico water softener in prep for new ECU. Professional installer points out that previous installation had brine dump to under the air conditioner. If I had fixed the water softener prior to this point, I would have rusted away the new air conditioner (just like the old one.)

 

It could but it depends on the increased install and operating costs. I'm not familiar with how the systems are presently arranged so I'm not sure what all the criteria might be.

I assume this uses water circulation from the tank to partially cool/condense the refrigerant? If so then replacing this with a dedicated glycol loop that runs through the tank or a second water loop to the tank should work. (It's hard to imagine it only running when hot water is being demanded.)

Depends, it is more likely to occur at the hot surface if it is lime based precipitation. Now if the surface is staying cool enough, and the additional heat added by gas/electric is much greater then you are probably right about where it will exceed the solubility. Sedimentation is a bit different (and depends on the composition/source of the sediment.) Sediment will drop out in still regions rather than in pores.

That would probably be the easiest and most cost effective way. It might require an intermediate glycol system that could be kept scale free. (You would need to change out the glycol periodically because the corrosion inhibitors eventually fail.) You probably wouldn't want to have to change out in the refrigerant containing lines at the condenser. If instead the exchange to the water itself was a small liquid/liquid double pipe (high heat transfer coefficients on both sides) it would be easy to make this part of cleanable inner pipe/tubing.

The problem for me in such systems is that I'm accustomed to steady state design while water heating and AC cycles are typically batch. Batch work requires more trial and error for optimization.

This would seem to be more expensive when the water heater and the condenser are not in close proximity since you have to do the exchange after the compressor. It also introduces some losses since there is only so much insulating of the lines that is possible.

Interesting problem, too bad that its application is limited to the cooling season.

 

This makes use of a "desuperheater"

In all cases, a plate style heat exchanger should be used. It's best to use a non-toxic treated water mix for the actual desuperheater, with the plate HX to separate the domestic water

That way, any water quality issues - eg hardness - won't cause expensive damage to your a/c system. The plate hx is fairly easy to clean, the ones that you take apart have a herringbone pattern inside, you can soak them for half an hour in vinegar.

 

Wow, that is low. Of course, as you note, when you measure fridge performance is also an important consideration. This time of year is pretty easy on them, while July and August are not. I had summer baselines for my appliances and now I'm remeasuring winter baselines for ones that are temperature sensitive.

My 22 cu. ft. 1994 model was sucking down 118 kWh/month :shocked: in the summer time frame (with 78-80 F indoors) but is running about 69 kWh/month now w/about 68-70 F indoors. Part of the difference might also be that I rigged up an attachment to thoroughly clean the coils last month, and back when I took the original baseline the fridge was running a few degrees colder than I wanted. So it appears that its real average usage is midway between. It's original energy guide average would be 72.5/month and estimated "aged" rating is 87.3/month.

And I think I have identified the one I want, 25 cu. ft., 476 kWh/year rating, with none of the in-dooor dispensers that waste so much space and jack up the price. It will save about 650 kWh/year, give me the storage area I need in the fridge section, and match the kitchen better... Since the old fridge works well and still looks good I hope to get $200 out of it by granting it "early retirement" from its duty here--essentially reimbursing me for swapping a few years early.

 

Those efficiency improvements came about due to environmental regulations, in other words the evil "tree huggers" are to "blame" for it

If it was up to the manufacturer, they'd still be selling fridges that suck up +500 kwh a month

 

Is anyone familiar with Sun Frost refridgerators and freezers? Their 16 cu ft combination refr/freezer is reportedly only 0.48 kWh per day at 70 deg F and 0.70 kWh for 90 deg F days.

 

I'm not familiar with them. They aren't pretty on the inside, but they have very thick insulation and it looks like a carefully separated hot section (coils) on top where it should be for a thermally efficient design.

 

Thanks for positive move i have inspire this posting. I guess that one way to clean out your fridge and freezer but I don't really recommend that method. Since it was the end of the month I didn't lose any meat because I didn't have much in the freezer. I did my first of the month grocery shopping the other day and have restocked a bit so I'm hoping my power will stay on consistently now. I'd hate to lose what I just put in the fridge and freezer. thanks for sharing knowledge...

 

I have heard a bunch about Sun Frost. The consensus in the solar community is that they are over price and they under perform relative to their cost. A modern energy star fridge will compete with a SunFrost at a much cheaper purchase price.

Any fridge can effectively have added insulation. If you built it into a properly vented cabinet to allow the condenser to cool, the top, back and sides of the cabinet can be insulated with additional layers of rigid foam.

For more info on sunfrost, go here and do a search for "Sunfrost": Solar Electric Discussion Forum by Northern Arizona Wind & Sun - Powered by vBulletin

Icarus

 

Much like emissions standards. A surprising number of hillbillies want to remove the emissions on their full size diesel powered pickups. Seems to me, if they want to live in a place with no emissions control, they should move to Mexico.

In particular, Mexico City. LA may have the worst air quality in the US, but it's spring fresh air in comparison to Mexico City.

 

Ordered the fridge today. LG 25 cu. ft. French door style with "Titanium" finish for ~$1400. I'll see what I can get out of the old one since it is still in excellent condition. This is not a project that's going to pay for itself in energy savings, but it should cut out about 50-60 kWh/month, minimum. What I've really done is hasten the retirement of the old one by a few years...and since it will have some salvage value this way (vs. zero), and the new one will provide some savings for those lost years, it is probably cost neutral for the overlap years compared to the cost of the new one applied to the same period.

Getting rid of the in-door dispenser system and overly large icemaker will increase the freezer space available. That took up 1/4 of the old freezer compartment.