Let’s talk about 30-40% of your electricity bill. That’s how much it costs the average homeowner or commercial building owner to provide proper heating, ventilating, and air-conditioning (HVAC). A good HVAC system is the key to maintaining a comfortable, healthy and interior environment. Through the years, I have been asked by many owners for a strategy to reduce their cost of energy and HVAC. They don’t want to sacrifice the interior environmental conditions, but they do want a point-by-point plan to follow. The interesting thing that often happens is that energy bills are lowered substantially and the HVAC system performance is improved. This is a standard function of any mechanical engineer specializing in energy and HVAC.
The information on this page will help homeowners, building owners and building operators make informed decisions about existing HVAC systems or future upgrades.
Operation and Maintenance
The first step to achieve energy and HVAC system optimization is load reduction. This step normally consists of a long range plan which itemizes the actions to be taken based on best return on investment. HVAC Reducing your building load allows the existing HVAC system to operate more efficiently. If a new system or systems are being considered, it will be more cost effective to design for the reduced load as opposed to the existing load. A few common load reduction strategies include:
Tighten the building shell and add additional insulation. Adding insulation in existing buildings may not be achievable in some instances, so more consideration should be aimed at the exterior shell, especially windows and doors.
Installing energy-efficient windows. This is a big item on some buildings that still have single pane windows. The installation of double pane windows with a thermal break is a great return on investment. Make sure they are ENERGY STAR qualified windows. Tinting or Low-E coatings will even be better.
Upgrading lighting systems. The average commercial building has a lighting density of 2-3 watts per square foot which maintains proper lighting levels. This is a significant part of the HVAC load and almost any efforts in this direction will lower the cooling requirement for the building. Accent lighting (sometimes called architectural lighting) are not always energy efficient and should not be considered if you want to reduce energy and HVAC costs. Energy-efficient lighting systems emit less heat into conditioned space than older incandescent technology. If you have a return air plenum instead of return air ductwork, consider light troffers so that some of the heat from the lights is returned to the HVAC system instead of going into the occupied area.
Selecting efficient equipment and electronic devices that have a power saver option will reduce the sensible heat gain in the space. Items to consider include copy machines, kitchen equipment, computers and refrigerators.
Control ventilation by having your outside air balanced. Most building owners have drawings of the original HVAC system installation. Have the drawings reviewed by a mechanical engineer to confirm your outside air flow rates conform to the latest code requirements. If no drawings are available, your mechanical engineer should still be able to make recommendations for improvement.
Addressing these items is your first step to reducing energy and HVAC costs.
The second step to achieve energy and HVAC system optimization is knowing your system. Your HVAC system is critical to your interior environment, but it also represents a large component of your utility expenses. While it is beyond the scope of this article to discuss every system, a few recommendations can be addressed. Every HVAC system component has increased in efficiency over the years. If your system is more than 13 years old, it’s time to begin planning for an upgrade to new equipment. Well maintained residential systems have a life expectancy of about 15 years or so but seem to fail at the worse times. Have a replacement plan ready for the day your equipment fails.
Commercial systems vary, but if your building is using packaged equipment or split systems, the same lifetime can be expected. For larger commercial systems and industrial applications, the HVAC system may be more complex and require an individual analysis by a mechanical engineer. As I said, HVAC systems vary and no one-size-fits-all analysis works for larger systems. What all these systems have in common is they are normally fueled by electricity. Electricity cost money, so any efforts in the direction of increased efficiency is a plus.