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Refrigeration

Refrigerant Oil Additives

Refrigerant oil additives are liquids designed to be introduced into all sorts of refrigeration systems, including air conditioners and chillers. According to vendors, these additives mix with refrigerant oil and improve heat transfer within refrigeration system heat exchangers. Vendors assert that the use of their products yields energy savings ranging from 5 to 30 percent of overall system energy consumption. It’s not clear that these additives can consistently produce savings in the ranges that vendors claim—in fact, lab and field tests by independent, qualified laboratories in…

Maintaining Packaged Rooftop Units

Packaged air-conditioner and heat-pump systems, also called rooftop units (RTUs), fall into disrepair over time, leading to energy waste and compromised comfort for a building’s occupants. It’s crucial to maintain these RTUs on a regular basis to ensure that they cool buildings and occupants as intended without wasting energy. Regular maintenance will also help to prevent or quickly catch malfunctions before they have a chance to further degrade the equipment or waste prodigious amounts of energy. An economizer stuck in the open position in a climate such as that of Tampa, Florida,…

Room Air Conditioners

A room air conditioner (RAC) cools the air, removes humidity, circulates air, filters out dust, and in some cases also provides heating. Although most RACs are designed for the residential market, about 20 percent of commercial buildings are cooled by them as well. Building operators and managers purchase RACs for one of several reasons: They want to cool selected rooms in an otherwise uncooled building. It isn't feasible to install central cooling in their building. They want to completely isolate one room from another (to avoid mixing air between rooms, so that each room has complete co…

Thermostats

Thermostats control HVAC operations to ensure occupant comfort, and they can cut energy costs when used correctly. In recent years a new type of thermostat we call “cloud” (also known as “smart” or “Internet-connected”) entered the market. We expect that cloud thermostats will become the new standard in HVAC controls for commercial buildings due to a combination of convenience and learning features, which make them an appealing replacement for nearly all existing thermostats. What Are the Options? There are three main types of thermostats: electromechanical, digital (also referr…

Packaged Rooftop Air Conditioners

The majority of US commercial floor space is cooled by self-contained, packaged air-conditioning and heat pump units, most of which sit on rooftops (Figure 1). These rooftop units (RTUs), also called unitary air conditioners or simply “packaged units,” are mass-produced machines that include cooling equipment, air-handling fans, and sometimes gas or electric heating equipment. RTUs are available in sizes ranging from 1 ton to more than 100 tons of air-conditioning capacity (1 ton of cooling capacity will remove 12,000 Btu of heat per hour). Figure 1: Up on the roof Rooftop…

Natural Gas Chillers

Though natural gas chillers have effectively served many end users over the past half century, all signs today are pointing to a drastic decline in the use of this technology. Manufacturers we spoke with reported that sales have dropped by up to 75 percent in the U.S. from approximately 2006 to 2010. Most—and for some manufacturers, all—new gas-fired chillers sold in the U.S. are being used to replace existing gas systems, not for new installations. According to one manufacturer, gas chiller sales for new installations are in decline worldwide. In addition, no gas-fired absorption …

Evaporative Cooling

Evaporative cooling is a process by which moisture is evaporated into an air stream in order to lower the air’s temperature. The resulting air stream can be used to cool a building, other air streams, or the components of an air-conditioning system. The lower the relative humidity, the greater the possible cooling effect when moisture is added. This technology is a versatile and energy-efficient alternative or adjunct to compressor-based cooling. In favorable climates (most of the western United States and other dry-climate areas worldwide), evaporative cooling can meet most or all build…

Economizers

If you are responsible for a cooling system that has a capacity of 7.5 tons or more, you probably have an air-side economizer—and chances are it could use some attention. When the outdoor temperature and humidity are mild, economizers save energy by cooling buildings with outside air rather than using refrigeration equipment to cool recirculated air (Figure 1). A properly operating economizer can cut energy costs by as much as 10 percent of a building’s total energy consumption (up to 20 percent in mild coastal climates), depending mostly on local climate and internal cooling…

Demand-Controlled Ventilation

Across the U.S., many stores keep long hours every day, and although they may be full of browsing shoppers during some hours of the week, relatively few customers will be milling about the floor space at other times. Occupancy fluctuations like these offer retail stores and other commercial facilities an opportunity for annual energy savings that can amount to as much as $1.00 per square foot (ft2). Instead of continuously ventilating the space at a constant rate designed to accommodate the maximum number of customers, building operators can implement demand-controlled ventilation (DCV) so tha…

Cool Thermal Storage

Thermal storage systems offer building owners the potential for substantial operating cost savings by using off-peak electricity to produce chilled water or ice for use in cooling during peak hours. The storage systems are most likely to be cost-effective in situations where A facility's maximum cooling load is much greater than the average load; The utility rate structure has high demand charges, ratchet charges, or a high differential between on- and off-peak energy rates; An existing cooling system is being expanded; An existing tank is available; Limited electric power is avai…

Centrifugal and Screw Chillers

In a typical commercial building, chillers consume more electricity than any other single energy-consuming device, except for an occasional extremely large fan. Thus, inefficient chillers can waste significant amounts of electricity, and even modest improvements in efficiency may yield substantial energy savings and attractive paybacks. However, it’s important to select a chiller (and its associated efficiency) carefully. Choosing a chiller that’s most efficient at full or part load, according to standard ratings, might be counterproductive because the ratings don’t measure t…

Electric Heat Pumps

Electric heat pumps are year-round space-conditioning systems capable of providing heating, cooling, and domestic hot water. Their appeal lies both in that they offer heating and cooling in a single piece of equipment—which usually means a lower capital cost—and in that they provide heat at a lower cost than electric resistance heating (in some cases, lower than gas heating as well). There are two broad categories of electric heat pumps—air source and ground source (also called geothermal). Air-source heat pumps are the most common form found in commercial applications, so we ha…

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