HVAC Efficiency: What You Need To Know
So much has changed in the world of air conditioning in recent years that if your system has almost any significant breakdown — or if it’s just not keeping you as cool as it used to — it may be worth replacing it instead of repairing it.
As of 2010, for example, manufacturers must use a new kind of refrigerant that’s not an ozone-depleting chlorofluorocarbon. And a new system can use less than half the electricity of your old one while doing a far better job of keeping you cool and comfortable.
Heating and cooling accounts for more than half of the energy use in a typical U.S. home, making it the largest energy expense for most homes.
If your air conditioner is more than eight years old, repair is probably not worth the expense, unless it’s a simple problem like debris clogging the condenser unit or a worn fan belt. Still, to best weigh your repair-or-replace decision, ask your contractor to assess not just the condition of your existing equipment, but also the ducts that deliver the cool air and the overall quality of the insulation in your house. Improving those elements might increase the effectiveness of the system as much or more than installing new machinery. Even if your central air conditioner is just eight to 10 years old, it could suck up to twice the electricity that even a low-end new one would use. That’s because it operates at or below 10 SEER, or Seasonal Energy Efficiency Ratio, which is the amount of energy needed to provide a specific cooling output. Until 2006, 10 SEER was standard, but these days, the minimum allowed by federal law is 14 SEER. That translates to 30% less electrical consumption and 30% lower cooling bills than equipment installed just a few years ago.
For an 1,800 square foot house, a new 14 SEER will suffice. You can double your energy savings by jumping up to 16 SEER, which has a higher price tag, but will reduce cooling expenses by 60% over a 10 SEER unit.
Heating Efficiency: What You Need To Know
Gas-fueled forced-air heating is the most common type in the United States. First, it pulls cold air from the house and passes it around a heated metal box called a heat exchanger. Then the heat exchanger transfers heat from the metal to the air. A blower fan then pushes the heated air through ducts that distribute it throughout the house.
Single-stage is like a stove where the knobs only have one setting: high. Since a single-stage furnace can only be on or off, the result is greater peaks and valleys in temperature, and more inefficiency.
- Two-stage has two settings, high and low. They’re better than single stage because they have a low-burning setting that keeps the heat from dropping too far below your desired point. And they’re more efficient because they keep the air temperature from varying as much as a single stage.
- A variable speed furnace can adjust the flame to any point between off and high. It constantly adjusts its flame to try to keep the air temperature constant. In theory, this results in greater comfort and better efficiency.
Load Reduction Before Heating and Cooling
One of the first steps you should consider in your home / facility before upgrading your heating and cooling system is to reduce your load (i.e. how much heating and cooling you actually use). Reducing your home’s load allows existing systems to operate less frequently and newer systems to be designed smaller, thereby lowering operating costs. Common load reduction strategies include:
“Tightening” your home’s shell and adding additional insulation to reduce leakage.
Installing energy-efficient windows such as energy star qualified windows. Upgrading lighting systems.
Energy-efficient lighting systems emit less heat into conditioned space than older inefficient technology.
- Consider implementing efforts to reduce heating and cooling load before selecting equipment.
- NEVER OVERSIZE! Avoid over sizing equipment at all costs. Over sizing equipment increases the capital cost at the time of the installation and the costs of operation of the equipment.
- When selecting a new cooling system, have your HVAC professional provide you a quote and specifications for a standard-efficiency and high-efficiency unit including lifecycle costs. If the lifecycle cost is less on the high-efficiency unit, purchase it.
- When purchasing Room Air Conditioners or Light Commercial heating and cooling units, select those units that are ENERGY STAR qualified.
- Consider energy recovery ventilation systems to reclaim waste energy from the exhaust air stream and use it to condition the incoming fresh air.
- In humid climates, consult your HVAC professional about supplemental dehumidification. By controlling humidity at your facility, you can increase occupant comfort and allow for further downsizing of equipment.
- Consider specifying economizers. Often available at a low incremental cost, these units draw in fresh air from the outside when the temperature outside is lower than the temperature inside.
- Install programmable thermostats and use automated settings to achieve savings.
- At a minimum, specify National Electrical Manufacturers Association (NEMA)premium motors on HVAC equipment, and consider specifying variable speed drives (VSD) on condenser and evaporator fans.
- In dry climates, consider evaporative coolers. These coolers use the evaporation of water to cool spaces, eliminating the need for energy intensive compressors.
- For facilities that have heat-generating processes such as cooking, or onsite distributed generation equipment, consider heat recovery as a way to capture free waste heat and use it to offset facility heating and cooling costs.
- For areas such as warehouses and garages, consider installing radiant heating. Radiant heating warms objects instead of the air, and requires less fuel. Radiant heat is also useful for warming exterior areas that require heating, such as patios and waiting areas.
- Many buildings are impacted by what goes on inside the building just as much as (and sometimes even more than) the weather conditions outside. That is why it is important to properly size equipment and consider the use of demand controlled ventilation system coupled with economizers to meet the internal loads of the building, e.g., commercial kitchens, computer data centers, etc.