Efficient Mechanical Systems Can Contribute to Building Energy Savings
Why retrofit your heating, ventilating and air-conditioning system?
The answer is because it very well may be the largest energy user in your building. Really? Many folks believe lighting is the largest energy user in buildings today. That is because most energy analysis and modeling is done by mechanical engineers, and we do a great job of presenting the energy-use data so it incorrectly shows that lighting energy usage is the problem and not our beloved mechanical systems. Sometimes we will show energy in terms of dollars instead of BTUs or kilowatts because gas is often much less expensive than electricity in many areas. Other times we simply show HVAC as separate categories–fans/pumps, heating, cooling and service-water heating, etc.–to make the lighting number stand out.
However, when you add heating, cooling and ventilating together and treat them as a single system (as they generally are), you are looking at about 45 to 70 percent of the building’s energy use. That certainly exceeds the usual 10 to 30 percent lighting figures. Of course a lot depends on climate, building type and building usage but, in general, HVAC should be a major target for those who are concerned about energy conservation.
Steps Toward HVAC Efficiency
Fantastic efforts have been made during the past decade or two to reduce lighting energy consumption. Lighting ballast and bulb change-outs have been the low-hanging fruit of electrical- and energy-services companies for years. Changing bulbs also is comfortable for most do-it-yourselfers. Although there still are millions more lighting upgrades that need to be identified and completed, we can almost assume you already know how to tackle this topic. But do you know how to reduce your HVAC energy consumption?
Fantastic efforts have been made during the past decade or two to reduce lighting energy consumption. But do you know how to reduce your HVAC energy consumption?
The first step is to reduce your loads. Do whatever you can to reduce the amount of heating and cooling required. This means better insulation and more of it. Get as much insulation as you can afford and install it correctly. Use ASHRAE’s “Advanced Energy Design Guide” series for climate-specific recommendations. (Free downloads are available at www.ashrae.org/aedg.) Improving your building envelope will reduce your heating and cooling needs.
If you don’t have windows with good thermal transmittance (U-Factor) and solar-heat-gain coefficient (SHGC), then you should retrofit them. Again, follow ASHRAE’s AEDG recommendations. U-Factor measures the heat transfer through a window, door or skylight and tells you how well the assembly insulates. The lower the U-Factor, the greater resistance to heat flow and the better the window’s insulation value. SHGC is the fraction of solar radiation admitted through a window, door or skylight. This tells you how well the assembly blocks heat caused by the sun. The lower SHGC, the less solar heat it transmits.