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Old 09-13-14, 01:59 PM   #1
Cleanriver
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Question heat pipes to preheat hot water tank?

Hi ECO DIYers,

I have a Geospring hybrid hot water heater. But in the endless pursuit of efficiency, I am thinking about using an assembly of "heat pipes" on my roof to pre-heat the tank water....assuming that will reduce water heating costs.

Although I have re-plumbed my entire house as the old copper sprung leaks, I am not strong on the integration of an outside heat source into an existing system.

I would appreciate any of the following:

1. Links to sites with schematics, and pitfalls
2. Your own experiences
3. Advice as to whether this is best bang for buck, or would you do something else?
4. Heat pipe sources, pref in US.

Background:
- location N. Va
- strong S exposure on "hip" roof, but not as spacious as the non-hip sides.

ANY advice gratefully appreciated!

Cleanriver

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Old 09-28-14, 09:05 AM   #2
gtojohn
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Perhaps add a solar water panel before to the geospring.
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Old 09-29-14, 07:25 PM   #3
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If you are thinking about the outdoor plumbing thing, PLEASE do a drain-back system of some kind. The small upfront expense of pumps and thermostats and such is so much less than busted, frozen, or melted pipes down the line.
Look here:

Solar Water Heating Projects and Plans

If you can eliminate the water from the outdoor collector, that would be ideal as far as reliability goes. Here's an idea:

Run some PV panels to the electric element in your geospring, or do as xringer has, and go buy a cheap(er) electric resistance heater that runs straight off the PV panels. When the sun is shining and your preheat tank is good, feed your extra power back to the grid through a micro-inverter.

He has been doing this for awhile now, and previously owned all manner of water-heating apparatus. Works like magic comparatively.

http://ecorenovator.org/forum/solar-...html#post29754

Last edited by jeff5may; 09-29-14 at 07:42 PM..
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Old 02-14-15, 09:01 PM   #4
menaus2
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I'm not sure what you mean by "heat pipes", but you want to go with an enclosed collector of some kind. I agree with Jeff that drainback is the way to go. No antifreeze to deal with and very reliable, keep it stupid simple. I've built a drainback solar preheater in a similar setup so hopefully I can be of some use.

A few things to keep in mind with a drainback: Make sure the pump has enough pressure to push the water the entire height of the pipe. Have a space between the water level of the tank and the bottom of the collector return pipe, you need a siphon break for proper drainback. Snake the pipe inside the collector with a downward slope, I've had good luck with pex-al-pex pipe as flexible, durable, and less expensive option.

A few other suggestions: Place the preheater as close to the water heater tank as possible, so you don't have as much "lag" before the preheated water reaches the heater. Twinwall polycarbonate is the way to go as far as glazing is concerned, the single wall I've used, while cheap, leaves more to be desired in terms of aesthetics and efficiency. If possible, base your collector box dimensions off of your glazing material dimensions. A little planning (as I've learned) would have reduced glazing scrap waste and resulted in a better looking finished product.

Depending on how you size your preheater, you might want to consider downsizing your water heater. If you are only heating water say 20f-30f from 90-100f to 120f, versus a 75f rise (55f to 120f) in a regular configuration, does it make sense to keep all that unnecessary heated mass sitting there 90% of the time slowly leaking thermal energy? You just want to double check the recovery time and be sure it works for your usage. Then again you have a sweet heatpump , so I wouldn't mess with it till its time to replace it.
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Old 06-06-15, 02:38 PM   #5
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Would this be effective in the winter? Canadian sinwin, that is. Our house has hot water piped to radiators as the heating system. But Canadian winters are probably far too cold.
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Old 06-06-15, 08:36 PM   #6
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Heatpipes are generally sealed copper tubes with a state change material in them (often and alcohol?) that boils at a low temperature at one end, and the vapor carries the heat to the other end. When it transfers the heat the other end of the heatpipe, it recondenses to a liquid and then it flows or wicks back to the other end. These are used in computer heatsinks and in solar heat collectors. They are very efficient at moving heat.
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Old 06-07-15, 04:02 PM   #7
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Quote:
Originally Posted by Thalass View Post
Would this be effective in the winter? ... But Canadian winters are probably far too cold.
We have cold winters here also and I have found it isn't the temperature that is important so much as the cloud. My system is at its most productive in late winter when it can be -30C or worse but the skies are often very clear. During the late autumn and winter the skies here are overcast and the heat production is basically nothing, even though it may be significantly warmer.

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