01-10-13, 09:01 AM | #311 |
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The cardboard exchanger is very interesting, I wonder if there are any mildew problems...
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01-10-13, 09:13 AM | #312 | ||
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Gasper,
Thanks for the links, especially the cardboard exchanger. What a concept! Quote:
Quote:
Not true? Best, -AC
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01-10-13, 09:47 AM | #313 |
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Mold happens in damp environments without much airflow. There is lots of airflow inside the recuperator, but there may be corners inside the HX core with less ventilation.
Also, moist cardboard gets soft, so I would imagine it would start to change shape sooner or later. Especially since in many climates both incoming and outgoing air can be quite humid. I believe this is similar to how condensing boilers/furnaces can be more than 100% efficient: It is the sum of the purely thermal heat exchange and heat from condensation.
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01-10-13, 10:57 AM | #314 | |
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Quote:
Do you actually think that this passes the 'smell test'? And, I also question the idea that condensing furnaces can be more than 100% efficient. Efficiency is defined as 'energy in' divided by 'energy out'. So the energy in is the total heat content of the fuel divided by the heat produced by burning the fuel. The total heat content also includes the latent heat of the moisture in the water by-product. Assuming we are talking about gas heat, non-condensing furnaces were able to hit almost 85% efficiency (probably not considering the blowers, etc). The newer ones which scavenge the latent heat in the water vapor are able to get up to 93% maybe even 97% (still not considering the blowers). I do realize that Europe has a better record on efficiency than the US, but exceeding 100% is in opposition to the laws of physics. Heat Pumps are able to have an efficiency of better than 100% because they are only making a small portion (maybe 28%) of the heat they provide, and they are moving and 'upgrading' the rest of the energy (ultimately it is solar) from the ground or air or water, into the house. So heat pumps are open systems and their efficiency rating is a bit of a fiction, at least on the cosmic scale. As far as the home owner is concerned, she pays for 1 watt and receives 3.5 watts, and she becomes very happy. Best, -AC
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01-10-13, 11:45 AM | #315 | ||
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Quote:
There was an efficiency scale used in the times before condensing units went mainstream, and on that scale 100% was the theoretical maximum of just the burner. When the new models became available, the same formula was used for the burner, then the condensing gain was added. This is more of a marketing scheme than physics. My new boiler's (Ariston Premium Evo System) manual claims: Quote:
If things can go faster than light, or be colder than absolute zero, then why not >100% efficiency?
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01-10-13, 12:33 PM | #316 |
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OK, I think I am beginning to see things with the EuroMind now...
But of course, this would be an Italian sports car... Naturally, this would be a Norwegian winter night... OK, OK, I am moving to Europe! -AC P.S.: (...and all this time, I thought that Texans had a monopoly on exaggeration...)
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01-10-13, 03:06 PM | #317 |
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I just read it somewhere that temperature efficiency can be more than 100%, but only if inside humidity is high and outside very low, but in practice you will never have high inside humidity with HRV, because the air coming in will practically have 0% humidity.
My point was that with HRV you can easily have over 90% temperature efficiency, while with ERV you will be struggling to get 80%. Energy transfer is not measured only by air temperature but also transferred humidity. This cardboard exchanger is by the words of his creator always dry, he had only one event when outside humidity was high 91% at 12°C and inside humidity was high >70%, he had a little humidity at air outlet, and this part of the exchanger was little bent. Freezing can be avoided with defrosting, this can be done with ventilating air only out thru the exchanger, cold air intake is shut down or run thru a bypass, this is done only to defrost (eg. 1 min), after that you can run it normally for 30 min and then perform defrost again. The other option is of course electric heater. |
01-10-13, 04:43 PM | #318 | ||
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Quote:
Quote:
(* I think one of the problems with the word "easily" is that it is too easily said *) In my experience, 90% efficiency in anything is not easily achieved. In fact the run of the mill cross-flow HRVs struggle to hit 60%. From researching I have done, only the very best devices that have been carefully designed to salvage the heat energy in outgoing air are able to reach anything approaching 90+% and they do it by salvaging the latent heat in water vapor in this case they are called Energy Recovery Ventilators. The devices that do not utilize the latent heat in water vapor are called Heat Recovery Ventilators... at least that's the way Wikipedia uses the terms. So, if you are convinced that a HRV can easily reach 90% efficiency, please send me your plans. I have time this weekend to easily whip one together. And please send me your efficiency formulas, for testing. The world will be a much better place for it. Best, -AC
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01-10-13, 08:31 PM | #319 |
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Combustion efficiency starts with the heating value of the fuel. Any fuel has two different heating values: Higher Heating Value (HHV) and Lower Heating Value (LHV).
The LHV is measured by burning an amount of the fuel in a bomb calorimeter and cooling the resulting gas to some temperature at which none of the water of combustion is condensed. The HHV is measured the same way, except that the gases of combustion are cooled to a lower temperature where most of the water is condensed. If you have a high efficiency condensing boiler or furnace, and you compare the resulting heat to the LHV, then you can get over 100% efficiency. If you compare to the HHV, you will not get over 100% efficiency. Last edited by JRMichler; 01-10-13 at 08:34 PM.. |
01-11-13, 11:31 AM | #320 | ||
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Quote:
Quote:
-AC
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Tags |
erv, heat recovery, hrv |
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