Energy Efficiency Rules of Thumb
Published on: October 19, 2019

Energy Efficiency experts are always asked to put together indicative projections before embarking on detailed energy analyses.  These typical values shown on this post may help you put together a quick analysis for your customers

Note: Do not assume these values to be LAWS. They are only typical values, which SHOULD BE VERIFIED for each application.

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General Information

Air Movement6 ACH
Ventilation Rate1 cfm/sf
5 cfm/person
Ventilation Rate5 CFM/person
Fan Energy1000-1500 CFM/hp
Electric Motors0.75 kW/hp
LightingT12s: 1.2 W/SQFT
T8s:  0.8 W/SQFT
LEDs:  0.4 W/SQFT
LEDs use 50% of CFLs
Chiller Size300-600 ft2/ton
Ton12,000 BTU/ton
Chilled Water2.4 GPM/ton (10° rise)
Condenser Water3 GPM/ton (10° rise)
Chiller InputAir Cooled Chillers: 1 kW/ton
Water Cooled Chillers: 0.6 kW/ton
Most Efficient Water Cooled Chillers: 0.35 kW/ton
Chillers & Pumps & Towers.9-1.0 kW/ton
Absorbers18 lbs steam/ton
Boiler Horsepower33,479 BTU/hr = 9.8 kW
Rebuilt Systems Design55°F supply air
30°-40° rise reheat coils
Dual Duct & Multizone Design55° cold deck
70-105° hot deck – with ODA Reset Schedule
VAV55°F cooling
10% box leakage flow
40-50% minimum fan volume
People Load450 BTU/person/hr
People DensityOffice: 140  ft2/person
Theater: 14 ft2/person
Heat TransmissionSee ASHRAE Handbook of Fundamentals
Glass1 BTU/ft2/°F
Good Wall0.1 BTU/ft2/°F
Masonry Wall0.15-0.3 BTU/ft2/°F
Thin Poor Wall0.25-0.5 BTU/ft2/°F
Overall Building0.15-0.5 BTU/ft2/°F
Infiltration0.5-1.5 ACH without Building Pressurization

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Chiller Efficiencies

Air-cooled
(including condenser power > 150 tons)
EERCOPkW/ton
ASHRAE Standard 90.1 19999.62.81.26
Good9.92.91.21
Best10.63.11.13
 
Water-cooled
(>300 ton centrifugal compressor)
 EERCOPkW/ton
ASHRAE Standard 90.1 199916.74.90.72
Good18.55.40.65
Best26.77.80.45

We borrowed this list from Abraxis Engineering.

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