HVAC equipment and systems

HVAC is an abbreviation for heating, ventilation, and air conditioning. HVAC systems in hospitality buildings serve to provide control of the interior temperature, humidity, air movement, and air quality within the structure. HVAC systems can be comprised of a number of components including boilers, chillers, centralized and decentralized guestroom HVAC units, larger roof mounted PTAC units, air handling units, and cooling towers. A boiler is a pressure vessel designed to transfer heat (produced by combustion) to a fluid. Boilers in most hospitality buildings provide hot water for heating use only and are generally relatively low pressure (up to 160 psig) and low temperature (under 200 -F, 93 -C). A few operations produce steam in boilers to meet needs of laundry operations or cooking equipment (or because the building itself was constructed in an era when steam was used for heating needs). If steam is produced (or purchased from a district heating system) it is usually put though a heat exchanger and hot water is produced for domestic purposes at the property or for space heating. Whether a steam or hot water boiler is used, the water in the boiler loop is usually contained in a closed loop and is chemically treated to prevent rust, corrosion, and other problems.

Boilers commonly burn natural gas although they may also use fuel oil and even propane. Boilers in hospitality are commonly made of cast iron or steel although some modular designs may utilize copper or stainless steel. Boilers require a flue to safely discharge the exhaust gases from combustion as well as other safety controls. A chiller is a device that creates chilled water for use in a centralized HVAC system. Most chillers use a vapor compression refrigeration system similar to that used by refrigeration equipment and air conditioners. These chillers may be reciprocating (for small applications), screw or reciprocating or scroll (for mediumsized applications) and screw or centrifugal for larger applications. It is also possible to have a chiller that uses heat as the primary energy source for its operation. Such chillers are referred to as absorption chillers. (The absorption chilling process is also used by some in room minibar units due to the quiet operation.) The chilled water is typically produced at between 44 and 50 -F (6 and 10 -C) and is circulated throughout the building using pumps. Heat rejection from the chiller is usually done using a cooling tower although heat rejection can also be done using a large fan coil rejecting heat to the air.

Efficiency of HVAC equipment usually expressed as the output of the equipment divided by the input. For building equipment, common measures of efficiency are:

- EER (energy efficiency ratio). This is the rated cooling capacity of a piece of cooling equipment (BTU per hour) divided by the watts consumed by the equipment. Typical values are 9–13.
- kW per ton (kilowatts per ton of refrigeration where a ton of refrigeration is 12,000 BTU per hour). Larger building cooling equipment such as building chillers are often rated in kW per ton, a ‘reverse’ efficiency measure where the input (kW) is divided by the output (tons of cooling). Typical values for modern chillers can be in the range of 0.45 to 0.6.
- COP (coefficient of performance). The rated heating capacity of a heat pump (BTU per hour) divided by the watts consumed by the equipment. Typical values are 2.5 to 3.5.
- Percent (%) boiler efficiency. Ranges of values from 75 to 95% can be found for modern equipment depending on the type of boiler.

Centralized and decentralized HVAC units are installed to condition the air in the guestrooms. Centralized units have fan coils and are connected to the building’s boiler and chiller for supplies of hot water or chilled water. Decentralized units operate using electricity as their power source and provide heating or cooling independent of central utilities. Decentralized units mix fresh air with return air in the units themselves. Most centralized units rely up fresh air being supplied from the corridor under the guestroom door. Air is exhausted from guestrooms via the ventilation fan in the bathroom. Some operations provide conditioned air to meeting areas and public spaces via packaged terminal air conditioners (PTAC) units. These are generally roof mounted. They provide space cooling and heating via the operation of a refrigeration system and gas heater or, in some instances, by connections with chilled and hot water supplies. Fresh air is introduced into the units from the roof area.

Another way to supply conditioned air to meeting rooms, ballrooms, corridors, and other public spaces is via air handling units. Air handling units consist of heating and cooling coils, filters, and fans. The heating and cooling coils are often supplied with hot water or chilled water although some may be what are called direct expansion (DX) utilizing a refrigeration evaporator in the air stream to create cooling. Fresh air is mixed with return air from building spaces, filtered, heated or cooled, and then returned to the spaces. Fresh air for the air handling units must be ducted from the outside and exhaust air from the building must be removed to the outside. A cooling tower is a heat rejection device, which rejects heat to the atmosphere though the cooling of a water stream to a lower temperature.

This cooling occurs by evaporation of water in the cooling tower. In hospitality buildings, cooling towers are common for rejection of heat from building chillers. They may also be used to reject heat from water source heat pumps and from water cooled foodservice refrigeration equipment. Cooling towers can potentially be large consumers of water at the property as well as of electricity to operate pumps and fans. Building management systems are installed in larger buildings to provide the facilities manager with the ability to monitor and control the distributed elements of the HVAC system from a central location. These systems allow for real time measurement and viewing of key operating parameters of the systems. The systems also allow the facilities manager to control the operation of the system with such features as time of day operation, modification of desired operating conditions, and staging priority in terms of equipment operation.

References
ASHRAE (2000) Boilers. In ASHRAE Systems and Equipment Handbook, ch. 27. Atlanta, GA: American Society of Heating, Refrigeration and Air Conditioning Engineers.

ASHRAE (2000) Liquid chilling systems. In ASHRAE Systems and Equipment Handbook, ch. 38. Atlanta, GA: American Society of Heating, Refrigeration and Air Conditioning Engineers.

Stipanuk, D.M. (2002) Hospitality Facilities Management and Design, 2nd edn., ch. 8. Lansing, MI: Educational Institute of the American Hotel and Lodging Association.