Online educational resource on achieving indoor environmental quality with radiant based HVAC systems
Not for profit educational resource on indoor environmental quality.
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ndoor Environmental Quality: particulate matter


Energy Efficient Indoor Environmental Quality Revolves around 75F (24C).
Bringing it all together - architecture, energy and indoor environmental quality.
Copyright Robert Bean, R.E.T., P.L. (Eng.), All world rights reserved.

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Ok we get it...the original graphic contained too much info one page so we've broken it down step by step...the 30 second message is sustainability revolves around one temperature...that being 75F or 24C. When you can design and construct high performance buildings - everything will be within 25F (14C) of 75F(24C) including body temperatures, fluid temperatures, discharge air temperatures etc...everything.

Performance categories

Description: Shown above - on the x-axis (bottom line) are heating and cooling fluxes (you might know them as heat losses and heat gains).  On the left hand side (y-axis, vertical) are various building enclosure performances from high [a] to poor [d] based on the heating and cooling flux. How did we determine these categories? Experience...we've been doing this for 30 years and after doing thousands of designs this in our opinion how buildings should be categorized (see overview of housing performance categories in North America).

Operating temperatures

Description: Now added are the surface and fluid temperatures. Make note that a poor performing building designated as [d] has a heating flux equal or greater to 40 Btu/hr ft2 (shown on x-axis). At such high heat loss, it is common to use fluid temperatures greater than 140F, also shown on the x-axis.

Core and skin temperatures

Description: Make note of the close relationship between human factors such as skin and core body temperature and operating temperatures typical of high performance buildings.

Thermal efficacy
Description: There is a significant increase in thermal efficacy (how homogenous the distribution of heat) in good to high performance buildings. Moderate to poor performing buildings have poor thermal efficacy.

Renewable energy
Description: The objective of sustainability is to stop using combustion and compression for occupant conditioning, this is possible with high performance buildings [category a] and renewable energy such as geothermal and solar thermal. Homes built to Passivehaus or R2000 standard are represented in this category. Homes built to typical North American standards are represented by the other categories [b], [c] and [d]. For commercial buildings, [a] type buildings would beat ASHRAE 90.1 by 50% and fall inline with Architecture 2030 and LEED's Platinum EA credits.

Efficiency and limitations
Description: Note that the further one moves away from a high performance buildings, not only does the efficacy and equipment efficiency go down, but also there becomes a greater risk for occupant and property damage due to the higher temperatures.

Radiant based HVAC systems
Description: When using high temperatures from combustion to heat our buildings we are destroying the opportunity to make better use of the fuel (see exergy efficiency). For example in a high performance building heated with radiant floor heating low VOC flooring and tight radiant tube spacing,  we only need 75F to 90F fluid temperatures even though we created 2800F temperatures in the furnace or boiler. At 2800F we could and should be generating power and heat - if society doesn't grasp this basic principle without a doubt it will remain the biggest challenge we have in achieving sustainability.

Exergy, sustainability, focal point
Description: When we apply human factor design principles, based on skin and core temperatures of the human body, to buildings we will naturally improve the indoor environment with more efficient buildings and less greenhouse gas emissions whilst preserving non renewable energy for future generations.

So now you know why we believe sustainable energy efficient indoor environmental quality revolves around 75F (24C).

Suggested reading

Myths and facts about radiant heating and cooling without the sales pitch.
Radiant gone wild - what happens when people treat radiant like a popular science experiment.
Radiant cooling - Yes it works when you learn the difference between sensible and latent cooling


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