The major considerations for the design of equipment rooms are as follows:
1. The overriding principle in equipment room design is to ensure that proper clearance is allowed within and around the room for installation, maintenance, and removal of equipment. This includes allowing access space around each piece of equipment for routine maintenance, allowing space within the equipment room or through doorways for significant maintenance work such as pulling tubes from boilers or chillers, and designing aisles within the equipment room to provide unobstructed clearance for equipment to be removed and reinstalled.
2. Equipment should be located within equipment rooms so that piping and ductwork are routed within the room and between interconnecting pieces of equipment in the most straightforward manner possible. Headroom within the equipment room is reduced wherever piping and ductwork need to cross each other or where they need to cross over equipment.
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3. All HVAC, plumbing, and electrical equipment required in each equipment room needs to be identified early in the design phase in order to avoid “surprises” at the end of the project. It is necessary for the HVAC system designer to coordinate with all other design disciplines to ensure that the equipment and associated clearance requirements of all disciplines are coordinated. For example, the HVAC equipment may be fed electrically from multiple panelboards located within the equipment room, or the HVAC equipment may be fed from a single motor control center located within the equipment room or in a different room of the building.
4. Working spaces around electrical equipment, such as the area required in front of electrical equipment connections, and dedicated equipment spaces, such as the clear space above electrical panelboards, must be respected in the HVAC system design. The HVAC system designer should never design piping or ductwork to be routed above electrical panelboards, and HVAC equipment should be located within the equipment room to ensure that the electrical working spaces are maintained.
5. The minimum height from the equipment room floor to the building structure above needs to be coordinated with the project architect and structural engineer. Normally a minimum height of approximately 10 ft is required if there will be piping only within the equipment room. A minimum height of approximately 13 ft is required if there will be ductwork in the equipment room as well as piping. These are only guidelines; it is necessary to coordinate the actual room height requirements with the equipment to be installed within the equipment room. Drawing a section at the most congested location in the equipment room is the best way to determine the minimum clear height required from the equipment room floor to the structure above.
6. Clear space should be allowed to remove plates from plate and frame heat exchangers for maintenance and to add additional plates if additional capacity is required in the future.
7. Chillers cannot be located in the same room as any combustion equipment unless the combustion equipment has a direct combustion air connection to the outdoors or the room is equipped with a refrigerant detection system that will automatically shut down the combustion process if a refrigerant leak is detected.
8. It is best to have at least one exterior building wall in the equipment room to facilitate the installation and removal of equipment. If the mechanical room is in the interior of a building, the corridors and doorways leading from the exterior doorway to the equipment room must be wide enough and high enough to install and remove equipment within the equipment room.
9. It is common to design double doors in equipment rooms for equipment installation and removal. The doors may need to be 8 ft high or higher to provide sufficient space for removal and installation of large equipment. 10. Floor drains connected to the building sanitary system are required near all
floor-mounted pumps, backflow preventers, system drains, cooling tower bleed pipe, and cooling tower overflow/drain pipe. It is common to design a floor drain between two adjacent floor-mounted pumps. Floor drains connected
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to the building storm water system are required to receive the condensate drainage from cooling coils in air handling units.
11. A makeup water line is required for all closed- and open-loop water systems. Typically a ¾- or 1-in. makeup water line is adequate.
12. ATC panels need to be located within equipment rooms in accessible locations. The size and number of ATC panels need to be coordinated with the ATC representative during the design phase.
13. The locations of the lighting fixtures within equipment rooms need to be coordinated with the equipment locations. The HVAC system designer should communicate the equipment room layout to the project electrical engineer as early in the design phase as possible so the lighting design can be coordinated. 14. The routing of boiler venting and pressure relief piping needs to be coordinated
within the equipment room and also outside the building.
15. Unit heaters are generally used to heat equipment rooms. Refer to Chap. 7 for more detailed information.
16. Air-conditioning systems are rarely used to maintain the space temperature within equipment rooms. Instead, ventilation systems are used to draw air from the outdoors in order to keep the room at a maximum of 10°F higher than the outdoor summer design temperature. The heat gains associated with the equipment motors, lighting, and exterior building envelope need to be included in the HVAC load calculation when determining the ventilation airflow requirement. Equipment rooms containing gas-fired or fuel-burning equipment are typically ventilated through a supply fan and relief air system in order to keep the room under positive air pressurization when ventilation is required. The supply fan can be wall- mounted, roof-mounted, or suspended within the room with a connection to the outdoors through a wall louver or rooftop intake air hood. Relief air is typically accommodated through a wall louver or rooftop relief air hood that is protected from backdrafts by either a backdraft damper or a motor-operated damper. If there is no gas-fired or fuel-burning equipment located within the room (or if this equipment has direct connections of outdoor combustion air), an exhaust fan and intake air system with motor-operated damper is preferred for ventilation in order to keep the room under negative pressurization, which reduces the transfer of odors from the equipment room to adjacent occupied spaces. Mechanical room ventilation systems are typically controlled by a space thermostat that is designed to operate the ventilation system whenever the space temperature exceeds 85°F. 17. Combustion air must be provided for all gas-fired and oil-burning appliances
located within the equipment room. Refer to NFPA Standard 54 —National Fuel
Gas Code or NFPA Standard 31—Standard for the Installation of Oil-Burning
Equipment for combustion air requirements.
18. Certain pieces of refrigeration equipment will require refrigerant pressure relief piping designed in accordance with the requirements of ANSI/ASHRAE
Standard 15-2010.
19. Equipment rooms housing refrigeration equipment may require refrigerant detection, exhaust, and alarm systems designed in accordance with ANSI/
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Endnotes
1. Natural gas and propane are gaseous fuels.
2. Fuel oil, which can refer to distillate fuel oils (lighter oils) or residual fuel oils (heavier oils), is a liquid fuel. The most commonly used fuel oil for fuel-burning appliances is Grade No. 2 distillate fuel oil (referred to as No. 2 fuel oil).
3. The term heating water is used in this chapter to refer to either heated water or heated brine.
4. Draft is the pressure difference that causes the products of combustion to flow through a gas-fired or fuel-burning appliance and vent system.
5. Condensing refers to the water vapor in the flue gas, whether it condenses within the combustion chamber of the boiler or not.
6. Low-pressure hot water boilers are limited to a maximum of 250°F water tempera- ture.
7. The gross output rating is equal to the input rating minus the heat that remains within the flue gas and is discharged through the vent system to the outdoors (referred to as the stack loss) minus the heat lost by the boiler surface to its sur- roundings.
8. I-B-R refers to the former Institute of Boiler and Radiator Manufacturers.
9. Pickup is an estimate of the load required to initially heat the working fluid and piping of an average system.
10. An appliance refers to any gas-fired or fuel-burning piece of equipment, including the burner.
11. The vertical portion of a vent system is referred to as the chimney.
12. The power venting fan must have a high temperature rating and be approved for installation in a vent system for gas-fired or fuel-burning equipment, whichever is applicable.
13. The dew point of water vapor in flue gas for typical natural gas combustion is approximately 130°F.
14. Combustion efficiency is equal to the input rating minus the stack loss divided by the input rating.
15. Thermal efficiency is the gross output rating divided by the input rating.
16. The heat transfer efficiency of a coil increases as the difference between the average temperature of the coil and the entering air temperature increases.
17. This assumes the heating water system is a closed system; that is, an open expansion tank is not used.
18. Although the water pressure at the point where the (closed) expansion tank con- nects to the system varies in proportion to the expansion of the water in the system, the water pressure at this point is not affected by the operation of the system pump. For this reason, the point where the (closed) expansion tank connects to the system is sometimes referred to as “the point of no pressure change” in the system. 19. Thermal shock occurs when the cast iron or steel components comprising the com-
bustion chamber and fluid pressure vessel of a boiler are subjected to a large tem- perature difference between the flue gas and return water. Thermal shock causes accelerated deterioration of these components and ultimately results in cracks and leaks in the combustion chamber and/or fluid pressure vessel.
20. The heating water supply temperature is normally reset based on outdoor tem- perature. As the outdoor temperature rises, the heating water supply temperature is lowered.
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21. When the pressure of steam condensate at pressures greater than atmospheric pres- sure is reduced to atmospheric pressure (or any pressure lower than the saturation pressure of the condensate), a portion of the condensate re-evaporates into what is called flash steam. For steam systems operating at 2 psig, the percentage of flash steam is minimal (0.7%) and need not be utilized. However, for steam systems operating at pressures exceeding 2 psig, it is recommended that the flash steam be utilized by steam equipment operating at a reduced steam pressure. Otherwise, this flash steam must be vented to the outdoors, which wastes its heating potential. 22. Although the steam condensate is returned by steam pressure motivation, con-
densate return piping should be pitched ½ in./10 ft in the direction of condensate flow.
23. Excessive dissolved oxygen in the boiler feedwater accelerates the corrosion of the fluid pressure vessel in the boiler.
24. Approach temperature = 200°F − 180°F = 20°F. 25. Approach temperature = 45°F − 38°F = 7°F.
26. Fouling factors have units of thermal resistance (ft2·h·°F/Btu).
27. This type of coil is called a direct expansion coil because the refrigerant within the coil expands, or evaporates, directly within the coil and, in the process, the refriger- ant absorbs heat from the air that is blown across the coil.
28. The cooler is called a direct expansion cooler when the refrigerant circulates through the tubes. It is called a flooded cooler when the refrigerant circulates through the shell.
29. One ton of refrigeration equals 12,000 British thermal units per hour (Btuh). 30. EER = [(100 tons) × (12,000 Btuh/ton)] / [(110 kW) × (1,000 W/kW)] = 10.9 EER. 31. Soft water has a low concentration of calcium and magnesium ions.
32. A water softener exchanges sodium ions for the calcium and magnesium ions in the water.
33. Increased space dehumidification can be accomplished and a decreased chilled water flow rate can be utilized with a lower chilled water supply temperature. However, these benefits come at the expense of decreased chiller energy efficiency.
34. A greater chilled water temperature rise requires that the cooling coils in the air systems and terminal equipment transfer heat from the air more efficiently. This increase in heat transfer efficiency is only achieved through a greater cooling coil fin surface, which translates to an increased first cost of the cooling coils and increased fan energy use.
35. Allowing the condenser water supply temperature to drop below 85°F when the out- door conditions are appropriate is a strategy that can reduce a chiller’s energy use. 36. Monitoring refers to receiving an input signal (either analog or digital) from a piece
of equipment. Control refers to sending an output signal (either analog or digital) to a piece of equipment. Refer to Chap. 9 for a more detailed discussion of automatic temperature controls and building automation systems.
37. Chiller operation can be controlled remotely through the BAS but is normally per- formed by the chiller control panel. Common points for monitoring through the BAS include chiller status, water temperatures, and alarms.
38. The flow or differential pressure switches are normally shipped with the chiller for field-installation in the piping.
39. Water flow through a cooling tower should be full flow to the distribution nozzles or full bypass to the sump. Full bypass to the sump is normally performed only during start-up to prevent unacceptably cold condenser water from being circulated
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C h a p t e r F o u rthrough the chiller condenser. Varying the flow of water through the distribution nozzles while the cooling tower fan(s) are running is not recommended because the percentage of the total water flow through the cooling tower that is evaporated increases, thereby increasing the rate of scale formation on the cooling tower fill. 40. An open system is one that is open to the atmosphere and operates under atmos-
pheric pressure.
41. A closed system is one that is not open to the atmosphere and is not subject to the limitations of atmospheric pressure.
42. Nonmechanical-draft cooling towers that do not contain fill or utilize a fan are available but are not frequently used for HVAC applications.
43. A contactor is a heavy-duty relay. A relay is an electromagnetic switch whose con- tacts are opened and closed by the presence or absence of current flow through a solenoid coil. Refer to Chap. 9 for a more detailed discussion of relays and their use in automatic temperature control systems.
44. Approach temperature, or simply approach, is equal to the leaving water tempera- ture minus the wet bulb temperature of the ambient air.
45. Wet bulb temperature is a measure of the moisture content of the ambient air and also gives an indication of the rate at which water evaporates in the ambient air. The evaporation rate increases as the wet bulb temperature of the ambient air decreases.
46. Approach = 85°F − 78°F = 7°F approach. 47. Range = 95°F − 85°F = 10°F range.
48. NPSHR is given in the manufacturer’s product data for the pump.
49. Nonmechanical-draft cooling towers, which induce air through the aspirating effect of water spray, are typically quieter than mechanical-draft cooling towers. However, this type of cooling tower is not a subject of this book because their application for HVAC systems is relatively limited.
50. Chemically treated cooling tower water is normally not discharged to the building storm water system unless the chemicals are biodegradable and it is acceptable to the authority having jurisdiction.
51. High water alkalinity (high pH) and low water hardness (soft water) are two factors that aggravate the formation of white rust.
52. The coefficient of performance (COP) for a compressor is the ratio of the refrig- eration output to the heat equivalent of the electrical input power. For example, a compressor that requires 0.88 kW (3,033 Btuh) of electrical input to produce 1.0 ton (12,000 Btuh) of refrigeration output would have a COP of 4.0 (12,000 Btuh output/ 3,033 Btuh input). A COP of 4.0 is typical for water-source heat pumps.