Note: Do not assume these values to be LAWS. They are only typical values, which SHOULD BE VERIFIED for each application. Also, if you’re interested in learning even more, here’s a free download for you: Standardized EMCS Energy Savings Calculations (20.3MB PDF)
» Rules of Thumb The following rules of thumb and other information are not intended for accurate load calculation or selection of equipment. It is for a very rough estimation to build an idea of what the anticipated load or capacity.
General Information
Air Movement | 6 ACH | |
1 CFM/ft2 | ||
Ventilation Rate | 5 CFM/person | |
Fan Energy | 1000-1500 CFM/hp | |
Electric Motors | 0.75 kW/hp | |
Lighting | T12s: 1.2 W/SQFT T8s: 0.8 W/SQFT LEDs: 0.4 W/SQFT LEDs use 50% of CFLs | |
Chiller Size | 300-600 ft2/ton | |
Ton | 12,000 BTU/ton | |
Chilled Water | 2.4 GPM/ton (10° rise) | |
Condenser Water | 3 GPM/ton (10° rise) | |
Chiller Input | Air 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 | |
Absorbers | 18 lbs steam/ton | |
Boiler Horsepower | 33,479 BTU/hr = 9.8 kW | |
Rebuilt Systems Design | 55°F supply air | |
30°-40° rise reheat coils | ||
Dual Duct & Multizone Design | 55° cold deck | |
70-105° hot deck – with ODA Reset Schedule | ||
VAV | 55°F cooling | |
10% box leakage flow | ||
40-50% minimum fan volume | ||
People Load | 450 BTU/person/hr | |
People Density | Office | 140 ft2/person |
Theater | 14 ft2/person | |
Heat Transmission | See ASHRAE Handbook of Fundamentals | |
Glass | 1 BTU/ft2/°F | |
Good Wall | 0.1 BTU/ft2/°F | |
Masonry Wall | 0.15-0.3 BTU/ft2/°F | |
Thin Poor Wall | 0.25-0.5 BTU/ft2/°F | |
Overall Building | 0.15-0.5 BTU/ft2/°F | |
Infiltration | 0.5-1.5 ACH without Building Pressurization |
Chiller Efficiencies
EER | COP | kW/ton | |
Air-cooled (including condenser power > 150 tons) | |||
ASHRAE Standard 90.1 1999 | 9.6 | 2.8 | 1.26 |
Good | 9.9 | 2.9 | 1.21 |
Best | 10.6 | 3.1 | 1.13 |
Water-cooled (>300 ton centrifugal compressor) | |||
ASHRAE Standard 90.1 1999 | 16.7 | 4.9 | 0.72 |
Good | 18.5 | 5.4 | 0.65 |
Best | 26.7 | 7.8 | 0.45 |
Headquarters
811 Palm StreetSan Luis Obispo, CA 93401
805 547 2050
Mailing Address
PO Box 1269San Luis Obispo, CA 93406
For software support, please email us at: [email protected]
Headquarter
811 Palm StreetSan Luis Obispo, CA 93401
805 547 2050
Mailing Address
PO Box 1269San Luis Obispo, CA 93406
For technical support, please email us at: [email protected]
The acronym HVAC stands for Heating/ Ventilating/ Air Conditioning. It's used to referto such systems for homes and businesses. In these systems, air moves between the inside andoutside of a home or other building. That means heat is continually lost or gained depending onthe climate and weather conditions. To install the correctly sized furnace or air conditioningunit, designers must apply calculations that factor in the amount of heat gained or lost.Contractors occasionally use 'rules of thumb' to size equipment for houses and businesses.
One rule of thumb estimates the average heat loss or gain based on the square footage of thestructure. For example, the builder may decide that it takes 1 ton (12,000 BTU) of air conditioningfor each 800 square feet of space. The problem is that climates, house size, season, number ofwindows and which direction they face, insulation, and the number of sunny days, to name a fewconditions, all make a difference. A heating/AC unit that's too big not only wastes energy andcosts more, it fails to maintain an even temperature, causes discomfort, and wreaks havoc on humidity levels.
Here are some things to consider when planning to install or replace heating and air conditioning:
- Installing the correct size keeps costs down.
- Correct humidity control prevents moisture damage from occurring.
- Installing properly sized units costs less and will pay for itself in energy savings.
- Cycling on and off is costly; if the furnace/air conditioner is sized correctly, it will maintainan even temperature.
- Properly sized HVAC requires less ductwork, which means lower cost.
- Correctly sized HVAC units help create a comfortable atmosphere for the building's inhabitants.
With fuel costs on the rise and environmental concerns at the forefront, it makes sense to gobeyond rule of thumb guesswork and carefully calculate our HVAC needs. For more informationon accurately measuring the heat load in your home, see our article onHVAC Sizing Calculations.