Proper Sizing of Central Air Conditioning

Whether you are looking to install a new central air conditioning unit or replacing a current unit, it is important to use the correct size unit. A that is too small will run continuously without adequately cooling the house, while a unit that is too big is overly costly and, due to frequent on/off cycles, can cause humidity problems.

Proper System Sizing 

In order to scientifically calculate the right central air conditioner size, you can perform a Residential Load Calculation. The sizing chart above is useful to help you determine your approximate central air conditioner size requirements.

Another way to size replacement air conditioners is to determine the system size that is currently in place. The manufacturers do not list the air conditioner size on the unit. The system capacity will be coded into the model number of the outdoor unit. For example, model CKL24-1 is a 2 ton unit.
Why? There are 12,000 Btu's per ton. The number 24 in the model number indicates the unit is 24,000 Btu's, divided by 12,000 Btu's per ton, equals 2 tons. 24,000 Btu's/12,000 Btu's per ton = 2 tons Use the following conversion information to determine your existing system size (use the system model number NOT the serial number) 18 = 1.5 tons 24 = 2 tons 30 = 2.5 tons 36 = 3 tons 42 = 3.5 tons 48 = 4 tons 60 = 5 tons.

When sizing air conditioners, be careful not to make the mistake of getting one that is too large. If the system you install is too large for the space, it will short cycle. In other words, the compressor will not run long enough to dehumidify the space and will limit your comfort. In addition, it will cycle on and off more frequently, increasing operating costs and reducing the system life.

Insulation Variables Variables such as your insulation, type and number of windows, number of stories, construction type, etc. will greatly affect the required Btu's per square for both heating and cooling. A general rule of thumb is that if your home is well insulated with newer style windows, you can select the smaller size system that falls within your total square footage.

If your home is two story it will place less of a load on the system in the downstairs area as the second floor acts as additional insulation. If your home is not well insulated, has older style windows, and/or a larger than average number of windows, you will want to select the larger system which falls within your square footage range. The less insulated and more windows within the environment, the more likely you will experience greater air and heat loss.

Proper air conditioner sizing is critical to optimize performance.

The HVAC Factor: Energy Recovery Ventilation

By Stephen J. Pargeter
Originally published in the August 2012 issue of Today’s Facility Manager

Studies have proven that outdoor air ventilation creates a healthful work environment. However, as these intake rates increase, so does the size, cost, and operating expense of the heating, ventilation, and air conditioning (HVAC) system. Facility managers (fms) are therefore caught between two powerful forces—the need to lower energy costs and the need to meet or exceed outdoor air ventilation regulations for occupant health and comfort.

During the ventilation process, large amounts of energy are wasted as HVAC systems replace indoor air with fresh outdoor air multiple times per day. The heating or cooling energy is continually lost in the exhaust air stream while new energy must be expended to condition entering outdoor air. Those who fail to capture wasted energy will continue to incur high energy costs.

To address this challenge, one option for fms is a site recovered energy technology such as energy recovery ventilation (ERV). Site recovered energy is any energy recovered on-site and reused to reduce the demand for more energy. Designed to operate with new or existing HVAC units, the ERV technology provides a means to cut energy costs without compromising outdoor air ventilation requirements.

While there are a number of air-to-air heat exchangers used in ERV, the most commonly used type in commercial and institutional buildings is a rotary heat exchanger (also known as an energy recovery wheel or enthalpy wheel). This wheel resolves the conflict between indoor air quality (IAQ) and energy conservation by recovering site energy normally wasted in exhaust air. It transfers energy by rotating between incoming (outdoor) and exhaust air streams to transfer heat and moisture from one air stream to the other, recycling up to 80% of this energy by preconditioning outdoor air for significantly reduced HVAC load and operating cost.

Rotary heat exchanger

Total energy saved depends on the wheel’s effectiveness and the difference in temperature and humidity between the two air streams. A bigger differential means larger energy savings.
For new and replacement projects, energy recovery costs are typically offset by lower first costs for an HVAC system. And significant reductions in fuel consumption provide healthy returns for the life of the HVAC system—instant to two-year paybacks in most North American climate zones. An energy recovery wheel may also be added to an existing HVAC system to improve efficiency.
HVAC systems with ERV improve control over humidity to minimize mold and mildew and reduce the risk of IAQ complaints and sick building syndrome, especially in humid climates. Meanwhile, many gas and electric utilities offer rebates for energy recovery to reduce peak demand and encourage energy conservation.

Organizations Using ERV
To meet new building codes, Dillard’s, a large apparel and home furnishings retailer, sought to increase outdoor air ventilation rates by a factor of three at its store in Palm Beach, FL. The two story building required approximately 50,000 cfm (cubic feet per minute) of outdoor air. Rather than add capacity to meet the increased load, management at Dillard’s installed rooftop units with integrated energy recovery wheels. By reducing the load by 160 tons, the retailer was able to choose units with that much less capacity. And by reducing peak demand by 215 kilowatts (kW), the company qualified for utility rebates that effectively paid for the wheels. The use of ERV is now standard for all Dillard’s stores.

Another example of this technology involves a major renovation at the Providence Career and Technical Academy (PCTA) in Providence, RI. The engineering team there chose to install a dual temperature, two pipe HVAC system with energy recovery wheels to maintain control of humidity during the shoulder season. The improved efficiency has yielded an estimated savings of $28,000 per year.

Another ERV adopter is the Eddy Village Green in Cohoes, NY, a nursing home complex of 16 housing units, each with 12 bedrooms. Each of those units has a 13 ton HVAC system with an integrated energy recovery wheel that supplies 3,500 cfm of outside air. In addition to an estimated upfront combined savings of $20,208 from installing smaller packaged units, the facility hopes to recover an estimated ongoing savings of $23,168 based on local utility rates.

Evaluating ERV Systems
Fms who are interested in finding out about the potential of ERV can begin by looking for the following characteristics in a system. These include products that feature:

• rating and certification by the Air-Conditioning, Heating and Refrigeration Institute (AHRI);
• high humidity (not just heat) transfer capability;
• easy accessibility and cleaning; and
• performance modeling software.

Fms should also look for established providers of these systems. Most mainstream HVAC equipment manufacturers offer energy recovery wheel options for new or existing applications.
The energy demand posed by outdoor air ventilation requirements is a pressing issue among fms eager to save money while still providing clean, healthy buildings. Energy recovery wheels offer a way to cut energy costs and supply ample outdoor air ventilation while also garnering a high return on investment.

Pargeter is vice president, Product Engineering, at Airxchange, a Rockland, MA manufacturer of energy recovery wheels. He holds a BSc (Honors) degree in Production Engineering and Production Management and has served on the board of directors of the Air-Conditioning, Heating and Refrigeration Institute (AHRI).

Air Conditioner Shortage In The Valley?

Is it true that there is an air conditioner shortage in the San Fernando Valley? We sent our reporters out to investigate the rumor.

Our first stop was to find out what company makes the most reliable Air Conditioning unit. We know that homeowners in the San Fernando Valley are smart enough to want the very best. The most trusted  independent rating magazine surveyed over 30,000 property owners and hands down the most reliable brand of home Air Conditioning equipment was American Standard.

The manufacturer's top American Standard air conditioner dealer in the San Fernando Valley, Kilowatt is located in Sherman Oaks right where the 101 meets Sepulveda.  We stopped by their cheerful office building to chat with owner Dean Gilford. "It's been over 100 degrees in the Valley every day this week," Dean said. "So people panic a little when their AC shuts down. They worry that there might not be enough product to supply all the extra demand when it gets this hot."

Dean assured us that there is no shortage of AC units. Just to prove that there was nothing to worry about we went to the warehouse in Van Nuys where hundreds of air conditioning units wait to be installed in homes throughout the Valley and Los Angeles.

 

Over the next few months Kilowatt will expertly install these air conditioners in homes and businesses from Malibu to Glendale. So rest assured that the Los Angeles air conditioning supply chain is in tact and ready to fill the needs of our healthy, happy communities.

Can next-gen building materials cut HVAC?

What if your building could regulate it's own temperature?

Smart-building materials have come a long way in the last decade: They're less toxic, more durable and more energy efficient than their predecessors. But the smartest materials available today still can't accomplish something that even the most primitive life forms can do -- keep their internal environment stable as outside conditions change.
It's called homeostasis. Healthy humans, for example, maintain body heat of about 98.6 degrees as outside temperatures vary, manage their oxygen and carbon-dioxide levels and also keep their blood pressures, salt and sugar contents from falling too low or climbing too high. Even amoebas maintain their osmotic pressure at a livable rate. And cells in all living organisms manage their levels of ATP, the substance that enables the production and flow of energy internally from one set of biochemical reactions to another.
"If you look at living organisms, one of the most basic things they can all do is regulate their own internal conditions," says Ximin He, a post-doctorate fellow at the Harvard School of Engineering and Applied Science and the Hansjorg Wyss Institute for Biologically Inspired Engineering. "It's how organisms survive in different seasons and face the constant challenges life throws at them," she says.
Now researchers at Harvard University and the University of Pittsburgh hope to create a new class of materials that can do the same thing. After about two years of research, the scientists have come up with a platform for creating materials that can self-regulate many different factors, including temperature, light, pressure or pH balance. And they've already invented one prototype: a thin water-based gel, or hydrogel, that automatically heats up when it's cold (and stops heating when it isn't) to maintain a constant temperature.
The research, unveiled in Nature in July, could have huge implications for smart buildings in Los Angeles. If future building materials could control their own temperatures, they might be able to eliminate the need for air conditioning and heating. Given that buildings account for nearly 39 percent of the U.S. energy use -- and heating, ventilation and air conditioning make up 64 percent of that 39 percent -- such a feat could significantly cut energy consumption and greenhouse-gas emissions.
It could also win these materials a piece of the booming sustainable-building market. Santa Monica, Calif.-based research firm IBISWorld expects the U.S. market will total $20.6 billion this year, up 7.3 percent from 2007, and reach $45.2 billion in five years.

For more info regarding energy efficient HVAC technology check out Jennifer Kho