Online educational resource on achieving indoor environmental quality with radiant based HVAC systems
Not for profit educational resource on indoor environmental quality.
 Bookmark and Share
snow melt and snow melting designs

eXergy (is not a spelling mistake)

Please be patient - this is a 5 mb files and will take 60 to 120 seconds to load. if you do not see the document it has not finished loading or you need the current version of Adobe Reader. Once completely uploaded, place cursor over document, use page up or page down.

First presented at the Southern Alberta Chapter of ASHRAE. Want to see this presentation? Contact us.

Above: Slides from ASHRAE Southern Alberta Chapter meeting.

In the context of using energy for heating and cooling, the word 'eXergy' describes the usefulness of the highest generated temperature and also reveals the wastefulness when supply temperatures are grossly mismatched to load temperatures. In reality, we must direct our efforts at eXergy since it can be destroyed whereas energy is conserved. To put this into practice, a high efficiency furnace or boiler may achieve a combustion efficiency of 97% but only 3% exergy efficiency. Exergy will get you to look at energy in a drastically different way.

Above: eXergy efficiency increases as the source temperature approaches the load temperature. In the case above, 2800F  at the burner of a furnace or boiler (upper right corner of illustration) is overkill for the 140F needed to deliver 70F space temperatures as such it only delvers 3% eXergy efficiency resulting in a destruction of otherwise potential useful work. It's like using a sledgehammer to drive in a finishing nail. If the 140F were supplied by a solar system or geothermal system the eXergy and energy efficiency would be in line and more sustainable.

Above: The higher exergy efficiency of a hydro powered ground source water to water heat pump is obtained by using it with low temperature radiant heating and high temperature radiant cooling which occurs with high performance buildings (< 10 Btu/hr/sf), using conductive floors (tile, slate, concrete) and tight tube densities (6" to 8" o.c.). Typical fluid temperatures for heating are 80F to 120F and for cooling 55F to 70F.

Suggested Reading
Factor E5 = Energy • Efficiency • Entropy • Exergy • Efficacy 

Home | Seminars | Solutions | Heating Cafe | Contribute | Online Help | Bean's Blog | About Us | Glossary
Privacy Policy | Legal | Contact Us | Site Map |
Carlson-Holohan Award| Send Us Your Comments

Copyright © 2012 Healthy Heating. All rights reserved.1 2 3
Site developed by
Donate using PayPal, Credit Cards Accepted