Appendix 13. Categories of Cooling and Heating systems

EcoShopping - Energy efficient & Cost competitive retrofitting solutions for Shopping buildings Co-funded by the European Commission within the 7 th Framework Programme. Grant Agreement no: 609180. 2013-09-01 2017-08-31 (48 months). Appendix 13. Categories of Cooling and Heating systems

EcoShopping Categories of Cooling and Heating systems Page 2 of 10 1 Cooling System Types HVAC system types in commercial buildings are broken down into three broad categories 1 : Central Packaged Individual AC. Central system: the cooling is generated in a central chiller and distributed to airhandling units or fan-coil units. Packaged system: This system consists on rooftop (or split) units with direct expansion cooling coils. Individual AC: This system is applied in external walls or windows. It is a selfcontained packaged cooling units. While the cooling is inside, the heat rejection occurs outside. 1.1 Central This HVAC system uses chilled water as a cooling medium. It can include air-cooled chillers as well as cooling towers. This system is very common for heating, which is generated by a boiler (in most cases) and distributed in hot water or steam piping. In Figure 1 it is shown a central system, which is divided into the subsystems: the airhandling unit, the chilled water plant, and the boiler plant. 2 Figure 1 Schematic of a Central System 1 http://www.descoenergy.com/pdf/commercial%20hvac%20energy%20consumption%20volume%201.pdf 2 http://apps1.eere.energy.gov/buildings/publications/pdfs/commercial_initiative/hvac_volume2_final_report.pdf

EcoShopping Categories of Cooling and Heating systems Page 3 of 10 The following is a description of the different units that comprise the central system: 1. Air-Handling Units In order to condition the air that is supplied to indoor spaces Air-Handling units are used in the central HVAC system. These units are usually manufactured in modular sections. In Figure 2, it is shown an Air-Handling unit Figure 2 Air-Handling unit

EcoShopping Categories of Cooling and Heating systems Page 4 of 10 The major types of components (modules) appear below: Filters Heating and/or cooling elements Humidifier Mixing chamber Blower/fan Balancing Heat recovery device Controls Vibration isolators Filters Air filtration is almost always presented in order to provide clean dust-free air to the building occupants Heating and/or cooling elements Although the AHU does not have heating neither cooling equipment (with the exception of a small electrical battery), inside the AHU there are one or two heat exchangers (providing heating or cooling, that come from boilers/chillers). With these heat exchangers the air temperature and humidity level will be modified. Humidifier In colder climates it is necessary to humidify the air, since the heating makes this air very dry decreasing the air quality level. There are different types of humidification: Evaporative, Vaporizer, Spray mist, Ultrasonic and Wetted medium. Mixing chamber In the mixing chamber it is mixed the right amount of cooler outside air with warmer return air can to improve the air quality of indoor air (fulfilling the minimum ventilation level required) and supplying the air at the needed temperature consuming the lowest energy.

EcoShopping Categories of Cooling and Heating systems Page 5 of 10 Blower/fan They are usually placed at the end of the AHU and the beginning of the supply ductwork Balancing Fans can vibrate. In order to solve this problem (noise), weights can be strategically placed to correct this vibration and achieve a smooth spin. Heat recovery device The heat recovery devices may be fitted to the air handler between supply and extract airstreams for energy savings. There are different typologies: Recuperator, Thermal wheel, Run around coil and Heat pipe. Controls Controls are the brain of the AHU, since they regulate all the aspects of an air handler: Flow rate of air, supply air temperature, mixed air temperature, humidity, air quality. Vibration isolators Blowers can vibrate transmitting the noise through the duct system. To avoid this problem, vibration isolators are normally inserted into the duct immediately before and after the air handler. In some AHUs it is also installed between the fan compartment and the rest of the AHU. 2. Terminal Units Terminal units provide local control of airflow in a large central air-conditioning system. There are different typologies of Terminal Units. The main ones are explained below: Single Duct Terminal A single duct terminal is composed by an air inlet assembly, which combines with an insulation liner and a discharge outlet. Typical accessories for this unit include a variety of liners, discharge attenuators, access doors and multiple outlets plenums. Low profile configurations can be used to suit applications where plenum space is restricted. a. Constant Volume Single Duct This Terminal Unit may or may not have an actuator, flow sensor and controls. If the unit does not have an actuator it is typically supplied with a manually locking quadrant allowing the damper blade to be locked into a single position. b. Variable Volume Single Duct A VAV single duct has a flow sensor, which works coupled with an actuator and control system. Depending on the control scheme selected, the VAV single duct will typically either provide a constant air volume or constant discharge pressure control. Dual Duct Terminals (Non-Mixing)

EcoShopping Categories of Cooling and Heating systems Page 6 of 10 A non-mixing dual duct terminal is essentially two single ducts fastened together with one common discharge opening. The inlets are connected to two of the following types of air supply: cold air supply; warm air supply; or fresh air supply. The non-mixing type of dual duct terminal has the potential to have thermally stratified discharge air and should have a minimum of three to five equivalent diameters of discharge duct to allow the different temperature air to mix. 3. Cooling Towers Cooling towers are used to cool condenser water for rejection of chiller condenser heat. Cooling towers can be classified as open or closed. In open towers, the condenser water contacts directly with cooling air. Most cooling towers for HVAC duty are open. In closed cooling towers, the condenser water flows in closed piping. Figure 3 below shows a typical cross-draft cooling tower with a propeller fan. Condenser water is distributed over the packing on either side of the tower which forces the water to flow in thin films, thus improving heat and mass transfer. Air is drawn in from the sides and discharges up through the fan grill. Some of the water evaporates during tower operation, thus enhancing cooling of the water. The condenser water system requires a fresh supply of water, which is supplied through a float valve in the tower sump. Some amount of condenser water must also be drained continuously to remove sediment. Figure 3 A Cooling Tower With A Propeller Fan In Figure 4 it appears a cooling tower that works with centrifugal fans. This kind of tower is quieter than the previous one, though it requires more fan power. It is used mostly for smaller applications. Figure 4 A Centrifugal-Fan Cooling Tower

EcoShopping Categories of Cooling and Heating systems Page 7 of 10 1.2 Packaged This cooling system is an air-air system, it doesn t use chilled water as intermediate cooling medium and directly provides the cooling to the air in a refrigerant evaporator coil. It is composed by: o Unitary system o Split systems For heating, these Packaged units have either a gas furnace or an electric resistive heating coil. Rooftop units can use outdoor air for cooling (free-cooling) when outdoor temperature is cool enough, using the outdoor and return dampers to mix the air. The air moves through a filter, the evaporator coil, the indoor blower and a furnace coil, and is supplied to the space through ductwork and supply diffusers. Below it is explained both mechanisms for cooling and heating with the packaged system: Ø Cooling for the unit is provided by a vapor compression cooling circuit. However, cooling is delivered directly to the supply air, and the heat is rejected in a condenser coil directly to the ambient air. In a split system, the two sides of the unit are separated, with refrigerant piped between them. A condensing unit, consisting of the refrigerant compressor, the condensing coil, and the condensing fan, is located externally. The indoor unit, consisting of the evaporator and indoor blower are located near or in the conditioned space.

EcoShopping Categories of Cooling and Heating systems Page 8 of 10 Ø Heating for the rooftop unit can be provided with a furnace, a resistance electric heat or by the vapor compression circuit operating as a heat pump. Most small rooftop units use draft inducing fans to move combustion products through the furnace coil. Some larger units use forced draft fans which push combustion air into the furnace. 1.3 Individual Room Air Conditioning Individual room air conditioning includes: Window AC units, frequently used in commercial applications. Packaged terminal air conditioners (PTAC s), commonly used in hotels and motels Packaged terminal heat pumps (PTHP s), commonly used in hotels and motels Water-loop heat pumps. The unit is mounted on an external wall, and a hole in the wall provides access to outdoor air, which is used for ventilation, heat rejection, and heat pumping (for the PTHP). Water loop heat pumps are similar to PTHP s except that water piped to the unit takes the place of the outdoor air. This allows more flexibility in placement of the unit, allows pumping of heat from warm to cool parts of the building through the circulated water loop, but requires installation of the water loop system. The water loop requires a cooling tower and a boiler for heat rejection or heat addition when the building thermal loads do not balance. 2 Heating System Types As explained above in the cooling systems sections, these HVAC equipments can be used also for heating. Additional information will be described below to give a clear idea of all the systems that can be integrated in the HVAC system of a shopping center. Heating system types can be classified fairly well by the heating equipment type. Main heating equipment used in commercial buildings includes the following types. District Heating Boilers (Oil and Gas) Furnaces (Oil, Gas, and Electric) Packaged HVAC Unit Furnaces (Gas and Electric) Packaged Heat Pumps Unit Heaters Packaged Terminal Heat Pumps Individual Space Heaters District heating and boiler-based heating systems have steam and/or water piping to distribute heat. The heating water may serve preheat coils in air handling units, reheat

EcoShopping Categories of Cooling and Heating systems Page 9 of 10 coils, and local radiators. Additional uses for the heating water are for heating of Sanitary Hot Water and other process needs, depending on the building type. Some central systems will have steam boilers rather than hot water boilers because of the need for steam for conditioning needs (humidifiers in air-handling units) or process needs (sterilizers in hospitals, direct-injection heating in laundries and dishwashers, etc.). For furnaces, either in heating-only units or in packaged units, the heat is distributed with ductwork. The same is true for packaged heat pumps. Most rooftop units use draft inducing fans to move combustion products through the furnace coil. Some larger units use forced draft fans which push combustion air into the furnace. Heat can also be provided by resistance electric heat or by the vapor compression circuit (operating as a heat pump). The remaining heating units heat the space directly and require little or no distribution. These include unit heaters, packaged terminal heat pumps, water-loop heat pumps and individual space heaters. 3 Summary of System Types The relationships between the system types and the heating and cooling equipment types is summarized in Table 1 below. Among the equipment types, some provide both heating and cooling, for instance the heat pumps of the cooling equipment group are the same heat pumps in the heating equipment group, while other equipment types do not have the same heating/cooling relationship. For instance, boilers can be used for heating in buildings with chillers, packaged AC, or room AC for cooling, or in buildings with no cooling.

EcoShopping Categories of Cooling and Heating systems Page 10 of 10 Table 1 Equipment Type Summary Space conditioning system type Central Constant Air Volume Variable Air Volume Fan-Coils Units Packaged Individual Not cooled Cooling equipment Central Chiller Rotary Screw Reciprocating Absorption Centrifugal Heat Pump Packaged Air-Conditioning Unit Residential-Type Central Air-Contidiones Packaged Terminal Heat Pump Water Loop Heat Pump Packaged Terminal Air Conditioner Room Air-Conditioner NONE These heating equipment types are not directly associated with any of the cooling equipment types or system types. Heating equipment Various heating equipment types are used in buildings with these cooling systems and equipment Heat Pump Packaged Unit Packaged Terminal Heat Pump Water Loop Heat Pump Various heating equipment types are used in buildings with these cooling systems and equipment Various heating equipment types are used in buildings with these cooling systems and equipment Various heating equipment types are used in buildings with these cooling systems and equipment Unit Heater Boiler District Heating Furnace Individual Space Heater Radiant Baseboard (electric)