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Old 11-29-11, 03:03 PM   #1
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Default Low Temperatuer Heating and High Temperature Cooling

The idea of low temperature heating and high temperature cooling (AKA: low exergy heating and cooling) has interested me for a few years now.

Today I came across a report regarding a novel design for heat exchangers that uses fine wires. Here is a quote from the report on fine wire heat exchangers (AKA: Fiwihex):

Quote:
When a heat exchanging system like a radiator is replaced by a Fiwihex, the energy that is needed in a room for heating still remains the same and is independent of the heat exchanging system. The important advantage of the Fiwihex is not that it needs less energy to heat a room, but that it needs energy of lower value. This makes it possible to use heat that would else have been worthless.

(emphasis mine)
Why is this important?

It is important in that it pertains to solar water and space heating.
Solar heating is regarded as low temperature heating. Conventional thinking is that when a reservoir of solar heated water becomes lower in temperature than 115F degrees, it is of little use in space heating. With attention to low temperature heating approaches, the minimum useful temperature can be significantly less than 115F degrees.

This can imply:
  • more days and hours that 'all-solar' heating can be used.
  • a smaller heat storing reservoir can be used.
  • less solar collector can be required.
It is also important to heat pumps, both ASHP and GSHP, since the higher temperature that a heat pump is called on to create (AKA: the higher the lift), the lower it's efficiency.

Another important possibility that low exergy places before us is the direct use of geothermal warmth and coolness, without the need of a heat pump for heating or air conditioning.

* * *

Information in the US about low exergy heating and cooling is not so easy to come by. There was an initiative started about 15 years ago by a group of mostly northern European countries to study this approach and to share information. The US was invited to become a member and/or to become a financial contributor to this initiative, but the US declined on both accounts.

The European consortium maintains a web site HERE.

There is an interesting page on the site called The Guidebook that may serve as an introduction.

There are books on the subject, but they are very expensive. Almost no libraries in the US carry books on this subject.

Perhaps we can share information here...

Best,

-AC_Hacker

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Old 12-01-11, 07:38 AM   #2
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I just installed a FiWi HEX radiator to a FiWi heat recovery ventilation unit which is connected to the 40m2 Solar Roof heating system in a house we are renovating to Passive House standard. I'm looking at a second FiWi HEX rad in my office for another project. I will pump 30 degree Celcius drain-back solar water through the FiWi HEX rad to heat the house.

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Old 12-01-11, 03:40 PM   #3
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This is our low grade heating method.
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Old 12-01-11, 05:20 PM   #4
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Quote:
Originally Posted by Viking House View Post
I just installed a FiWi HEX radiator to a FiWi heat recovery ventilation unit which is connected to the 40m2 Solar Roof heating system in a house we are renovating to Passive House standard. I'm looking at a second FiWi HEX rad in my office for another project. I will pump 30 degree Celcius drain-back solar water through the FiWi HEX rad to heat the house.
So, as far as I can see, there are air-to-air FiWiHex and also Water-to-air FiWiHex exchangers, am I correct?

Are you utilizing both types?

-AC_Hacker
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Old 12-01-11, 05:26 PM   #5
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Quote:
Originally Posted by AC_Hacker View Post
So, as far as I can see, there are ait-to-air FiWiHex and also Water-to-air FiWiHex exchangers, am I correct? Are you utilizing both types?-AC_Hacker
Yes! I use both types but I use the air/air the most.
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Old 12-01-11, 06:16 PM   #6
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Quote:
Originally Posted by Viking House View Post
Yes! I use both types but I use the air/air the most.
I assume that you are using the water type for your solar heated water, right?

Do you know what temperature range the water-to-air HXs will work in?

Is there a possibility that the FiWiHex liquid-to-air HXs can be used for refrigerant? It seems that if the really low-temperature heat exchanges are possible, it would work amazingly well in heat pump applications, too.

-AC_Hacker
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Old 05-04-12, 05:00 PM   #7
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Default Low Exergy Information and Tools

Low Exergy heating and cooling is very interesting, as it is more a shift in overall thinking about energy and how it is best used. On the surface, many of the ideas seem to be so obvious as to be of little value, but taken as a whole, the ideas constitute a paradigm shift.

* * *


In my efforts to locate information on Low Exergy heating and cooling, I have recently come across some promising resources...
  • LowEx.net
    This is the original on-line information repository that I discovered. I don't think it is being actively maintained, but by using the Wayback Machine, dead links may still come to life.
  • Annex49.com
    This is my recent discovery. It looks to be fairly current, and most links are working.
  • Annex49 Materials page
    This is the most useful page at annex49 that I found. Quite a few informational PDFs and also some spreadsheet exergy-assessment tools.
At Annex49, there is also a page with articles and reports on various aspects of Low Exergy research. The reports are not free, but by using WorldCat many of the reports and papers can be found in libraries throughout the world. If a Inter-Library Loan card is applied from any library, most of these resources can be gotten for little or no money... sometimes delivered through the mail, or gotten as free eBooks.

Best,

-AC
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Old 05-07-12, 10:01 AM   #8
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I am planning a low heat project now. The plan is to run PEX ALU under a standing seam metal roof, pull off the heat & bring it inside a super insulated building for underfloor heating. Building is R70 roof, R 50 walls, R40 under the slab in Philadelphia, PA area. Double stud wall construction - no thermal bridges. .6 ACH
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Old 05-07-12, 10:29 AM   #9
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Sounds like a great idea to me. Are you planning on having a hot water tank, or thermal mass in the flooring, or none at all?
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Old 05-07-12, 11:24 AM   #10
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I am thinking of sand bed storage under floor. Floor will probably be slate.

Heat regulation summer = shunt to nearby swimming pool
Heat regulation in winter = open the window.


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