Building Utilities 2 – Electrical, Electronics, and Mechanical Systems Module 1: Thermal Comfort PDF

BUILDING UTILITIES 2 – ELECTRICAL, ELECTRONICS, AND MECHANICAL SYSTEMS MODULE 1: Thermal Comfort 1 THERMAL COMFORT OBJECTIVES OF A BUILDING ▪ To create shelter from the climate ▪ To facilitate human activities within the building ▪ To enhance thermal comfort. INTE...

BUILDING UTILITIES 2 – ELECTRICAL, ELECTRONICS, AND MECHANICAL SYSTEMS MODULE 1: Thermal Comfort 1 THERMAL COMFORT OBJECTIVES OF A BUILDING ▪ To create shelter from the climate ▪ To facilitate human activities within the building ▪ To enhance thermal comfort. INTERRELATIONSHIP AMONG ▪ Man – adaptive behavior ▪ Building – determined by envelope ▪ Climate – what we expect During the facility design and development process, projects must have a comprehensive, integrated perspective that seeks to: ▪ Facilitate indoor environmental quality ▪ Value aesthetic decisions ▪ Provide thermal comfort ▪ Supply adequate levels and quality of ventilation ▪ Prevent airborne bacteria, mold, and other fungi, as well as radon gas ▪ Use materials that do not emit pollutants or are low-emitting ▪ Assure acoustic privacy and comfort ▪ Control disturbing odors ▪ Pursue energy efficient strategies ▪ Create a high-performance luminous environment ▪ Provide quality water THE HUMAN BODY ▪ Thermal and atmospheric conditions in an enclosed space are usually controlled to ensure:  the health and comfort of the occupants or,  the proper functioning of sensitive electronic equipment, such as computers, or certain manufacturing processes that have a limited range of temperature and humidity tolerance. ▪ The physiological characteristics of the human body allow it to withstand great variations in thermal conditions. ▪ Man has a very effective temperature regulatory system - which ensures that the body’s core temperature is kept at approximately 37°C ▪ The two most important sets of sensors for the control system are however known.  The hypothalamus-sensor is a heat sensor which starts the body’s cooling function when the body’s core temperature exceeds 37°C. C5S1_BUTILI2_MOD1 pg. 1   The skin-sensors are cold sensors which start the body’s defense against cooling down when the skin temperature falls below 34°C. ▪ Signals from these two sensor systems form the basis for evaluation of the thermal environment. ▪ It takes some time to change the body’s core temperature ▪ If the hot and cold sensors output signals at the same time, our brain will inhibit one or both of the body’s defense reactions. METABOLISM ▪ The human body is a heat generator. ▪ People oxidize the food taken into the body, converting it into electrochemical energy. ▪ The rate at which we generate heat (our metabolic rate) depends mostly upon our level of muscular activity ▪ As with all conversions from one form of energy to another, there is a certain conversion efficiency. ▪ This results in the continuous generation of heat within the body, which must be rejected by means of sensible heat flow ▪ If more food energy is ingested than is needed, it is stored as fat tissue for later use. ▪ MET is a unit of measurement of body heat production, in which one (1) MET is equal to 18.4 Btu/h/ft2 or 58.2 W/m2, the energy produced by a sedentary person. ▪ Under these conditions, the total heat produced by an average adult - with a body surface area of 19.6 ft2 or 1.8 m2 - is about 360 Btu/h (106 W). C5S1_BUTILI2_MOD1 pg. 2  ▪ To maintain thermal comfort:  The actual combination of skin temperature and the body’s core temperature should provide a sensation of thermal neutrality.  The fulfilment of the body’ s energy balance: the heat produced by the metabolism should be equal to the amount of heat lost from the body. HEAT TRANSFER ▪ Heat is a form of energy that flows from a point at one temperature to another point at a lower temperature. ▪ The common measure of quantity of heat energy in the English system of units is the British thermal unit (Btu).  It is that heat energy required to raise 1 pound of water to 1° Fahrenheit.  The rate of flow of heat in these units is expressed in Btu per hour (Btuh). ▪ Heat transfer is the process of energy transfer through a medium due to a temperature difference. There are three main modes of heat transfer and one thermal process that involves heat loss only. Conduction ▪ Heat is transferred directly from molecule to molecule within or between materials ▪ Conductive heat transfer occurs through a solid material anytime there is a difference in temperature between the two sides of the material ▪ The thicker the material, the slower it will conduct heat Convection ▪ Heat is exchanged between a fluid (typically air) and a solid, with the motion of a fluid playing a critical role in the extent of heat transfer ▪ In short, convective heat transfer in buildings is caused by air movement Radiation ▪ Heat flows via electro-magnetic waves from hotter surfaces to detached colder ones - across empty space and potentially great distances ▪ When such a wave strikes a barrier, part of it reflected, part of it is absorbed, and sometimes part of it is transmitted ▪ Occurs between bodies that exist in line-of-sight ▪ Radiant heat cannot go around corners Evaporation ▪ A one-way thermal process involving heat loss only, or exclusively a cooling mechanism. ▪ Liquid is used to facilitate removal of heat (in the case of human body, sweat glands) ▪ A liquid can evaporate only by removing large quantities of heat from the surface it is leaving C5S1_BUTILI2_MOD1 pg. 3 Remember! ▪ As air and surface temperatures approach our own body temperature, we lose the options of convection, conduction, and radiation. Evaporation becomes essential, so access to dry, moving air is greatly appreciated. ▪ As air and surface temperatures fall, evaporation decreases while convection, conduction, and particularly radiation increase. FORMS OF HEAT 1. Sensible Heat – is that which causes a change in temperature when it is added or removed 2. Latent Heat – is that which causes a change of state in the substance, from solid to liquid to gas or vapor, while the temperature remains constant when it is added or removed Note: The amount of heat that must be added to or removed from a unit mass of substance to change its temperature by one degree is known as the specific heat of that substance. 3. Enthalpy – the sum of the sensible and latent heat of a substance. For example, the air in our ambient environment is a mixture of air and water vapor. If the total heat content or enthalpy of air is known, and the enthalpy of the desired comfort condition is also known, the difference between them is the enthalpy or heat that must be added (by heating and humidification) or removed (by cooling and dehumidification). C5S1_BUTILI2_MOD1 pg. 4 THERMAL COMFORT ▪ A feeling of well-being ▪ Simply a lack of discomfort ▪ That condition of mind which expresses satisfaction with the thermal environment that is influenced by physical and physiological factors. ▪ Thermal comfort is calculated as a heat transfer energy balance.  Heat transfer through radiation, convection, and conduction are balanced against the occupant’s metabolic rate. THERMAL COMFORT FACTORS 1. Environmental Factors a. Air Temperature – The temperature of the air tat a person is in contact with, measured by the dry bulb temperature (DBT). b. Air Velocity – The velocity of the air that a person is in contact with (measure in fpm or …) c. Radiant Temperature – The temperature of a person’s surroundings (including surfaces, heat generating equipment, the sun, and the sky). This is generally expressed as Mean Radiant Temperature.  To lessen radiant temperature, you let the natural ground grow. d. Relative Humidity (RH) – The ratio between the actual amount of water vapor in the air and the maximum amount of water vapor that the air can hold at that air temperature, expressed as a percentage.  Between 30 – 70% (normal/comfortable)  29% below (need for humidifier)  71% above (need for dehumidifier) 2. Personal Factors a. Clothing Insulation – Clothes insulate a person from exchanging heat with the surrounding air and surfaces as well as affecting the loss of heat through the evaporation of sweat. b. Metabolic Heat – The heat we produce through physical activity. PROPOSED NORMS FOR ENVIRONMENTAL FACTORS Environmental Factors Proposed Norms Air temperature 21°C Average radiant temperature ≥ 21°C Relative humidity 30 – 70 % Speed of air flow 0.05 – 0/1 meter/second Temperature gradient (from head to foot) ≤ 2.5°C C5S1_BUTILI2_MOD1 pg. 5 Generally, the corrections that should be carried out are the following: The air temperature should be increased: The air temperature should be decreased: ▪ If the speed of the air flow is high ▪ If the speed of the air flow is low ▪ For sedentary work situations ▪ Is the work involving heavy manual labor ▪ If clothing is used light ▪ When warm clothing is used ▪ When people must be acclimatized to high indoor temperatures LOCAL THERMAL DISCOMFORT ▪ Even though a person has a sensation of thermal neutrality, parts of the body may be exposed to conditions that result in thermal discomfort. ▪ This local thermal discomfort cannot be removed by raising or lowering the temperature of the enclosure. ▪ It is necessary to remove the cause of the localized over-heating or cooling. ▪ Generally, local thermal discomfort can be grouped under one of four headings. 1. Draught ▪ Draughts are the most common complaint when talking about indoor climate in air-conditioned buildings, vehicles and airplanes. It is about unwanted local cooling of the body. C5S1_BUTILI2_MOD1 pg. 6  ▪ The amount of heat loss from the skin caused by draughts is dependent on the average air velocity, as well as the turbulence in the airflow and the temperature of the air. ▪ A high turbulent airflow is more annoying than a low turbulent airflow, even though they result in the same heat loss. 2. Asymmetry of Thermal Radiation ▪ If a person stands in front of a blazing bonfire on a cold day, his back will begin to feel uncomfortably cold after a period of time. ▪ This discomfort cannot be remedied by moving closer to the fire, resulting in an increased body temperature. ▪ Experiments exposing people to changing degrees of radiant temperature asymmetry have proved that warm ceilings and cold windows cause the greatest discomfort, while cold ceilings and warm walls cause the least discomfort. 3. Vertical Air Temperature Difference ▪ Generally, it is unpleasant to be warm around the head while at the same time being cold around the feet. ▪ A 3°C air temperature difference between head and feet is a dissatisfaction level. ▪ The Vertical Air Temperature difference is expressed as the difference between the Air Temperature at ankle level and the Air Temperature at neck level. 4. Floor Temperature ▪ Due to the direct contact between feet and floor, local discomfort of the feet can often be caused by too high or too low a floor temperature.  It is the heat loss from the feet that causes the discomfort. The heat loss depends on parameters other than the floor temperature.  It is the difference in conductivity and heat capacity that makes cork floors feel warm to the touch while marble floors feel cold. ▪ If people wear "normal indoor footwear" the floor material is less significant.  This leads to acceptable Floor Temperatures ranging from 19°C to 29°C. ▪ Different recommendations are valid for floors occupied by people with bare feet. Remember, only when both the local and general thermal comfort parameters have been investigated, can the quality of the thermal environment be judged. CLOTHING ▪ Clothing reduces the body’s heat loss. ▪ The unit normally used for measuring clothing’s insulation is the Clo unit, but the more technical unit m2°C/W is also seen frequently (1 Clo = 0.155 m2°C/W or 0.88 ft2hr°F/Btu). ▪ The Clo scale is designed so that a naked person has a Clo value of 0.0 and someone wearing a typical business suit has a Clo value of 1.0. C5S1_BUTILI2_MOD1 pg. 7  ▪ The Clo value can be calculated if the person’s dress and the Clo values for the individual garments are known, by simply adding the Clo values together and multiplying the sum by 0.82. Clo VALUES FOR INDIVIDUAL ITEMS OF CLOTHING THE BUILDING ENVELOPE ▪ People in urban settings spend between 80-90% of their time in indoor spaces while carrying out sedentary activities, both during work and during leisure time. ▪ This fact led to the creation of environments within these indoor spaces that were more comfortable and homogeneous than those found outdoors with their changing climatic conditions. ▪ To make this possible, the air within these spaces had to be conditioned; warmed during the cold season and cooled during the hot season. C5S1_BUTILI2_MOD1 pg. 8  ▪ For air conditioning to be efficient and cost-effective it was necessary to control the air coming into the buildings from the outside. ▪ The result was increasingly airtight buildings and more stringent control of the amount of ambient air that was used to renew stagnant indoor air. THERMAL PROPERTIES OF BUILDING ENVELOPE COMPONENTS 1. Conductivity  A characteristic rate at which heat will flow through each material (Btu/hr that flow through 1 sq. ft. of the material that is 1-inch thick when the temperature difference across that material is 1°F) 2. Conductance  Refers to thermal heat transfer of specific material of specific thickness  Used to describe heat flow through defined sizes/thicknesses of modular units of non- homogeneous materials.  For materials that come in various standard thicknesses, it is useful to know that rate of heat flow for that standard thickness instead of the rate per inch. 3. Resistance  Indicates how effective any material is as an insulator, reciprocal of conductance  Measured in hours needed for 1Btu to flow through 1sf of a given thickness of a material when the temperature difference across that material is 1oF 4. Emittance  Ratio of radiation emitted by a given material to that emitted by a blackbody at the same temperature  The lower the emittance, the lower the radiative heat exchange.  Shiny materials are much less able to radiate than common rough materials THERMAL CLASSIFICATION OF MATERIALS ▪ Insulators – retard the heat flow; useful for thermal barriers ▪ Conductors – encourage heat flow; dense, durable and diffuse heat readily; useful for thermal storage materials C5S1_BUTILI2_MOD1 pg. 9 CATEGORIES OF INSULATION MATERIALS 1. Organic  Renewable materials (plant/animal derived) Cellulose. Cork. Woodfibre. Hemp fiber. Flax wool. Sheep’s wool.  Fibrous or cellular products (cotton, synthetic fibers, cork, foamed rubber, polystyrene) 2. Inorganic  Fibrous or cellular products (glass, rock, wool, perlite, sag wool, vermiculite) 3. Metallic or Metalized Organic Reflective Membranes  Must face an air space to be effective  Available in sheets or rolls of either single or multiple layers, sometimes pre-formed shapes with integral air spaces INFILTRATION ISSUES ▪ Infiltration is when air enters or leaves the building as a result of unintentional gaps in the building envelope, and/or between the insulation and the framing of a building. ▪ This allows outside air to bypass the insulation and convectively cool or heat interior spaces. ▪ Buildings in cold climates are more sensitive to infiltration of outside air. ▪ Buildings in moderate climates and/or with warm internal environment are less sensitive to infiltration and can even benefit from reduced cooling energy use due to the natural ventilation qualities of infiltration. ▪ Buildings in very hot climates are only moderately sensitive to infiltration due to the lower temperature differential between outside and inside. ▪ Commercial building air handling systems are generally designed for positive pressure, meaning infiltration is reduced when the system is operating. 2 PRINCIPLES OF AIR CONDITIONING SYSTEMS The goal is to keep it more comfortable inside the house than it is outside. C5S1_BUTILI2_MOD1 pg. 10 REFIGERATION vs AIR CONDITIONING ▪ Refrigeration refers to processes that take thermal energy (heat) away from a place and gives off that energy to a place with a higher temperature.  Naturally, heat flows from a place with a higher temperature to a place with a lower temperature.  Therefore, refrigeration runs against the natural heat flow and so it requires an additional work to be done. ▪ Air conditioning is a part of refrigeration where thermal energy (heat) is taken away from the air in a large space such as a room or a vehicle.  Air conditioners are fitted into rooms so that they cool the air inside them.  Modern age air conditioners are not only concerned with maintaining the temperature of the air; they also help to regulate humidity, filter the air and keep toxic gases out of human reach. AIR CONDITIONING UNITS DON’T CREATE COOL AIR. ▪ What they actually do is remove heat out of a given space. ▪ In summary, refrigeration systems are used to remove heat from one space and transfer it to another location. ▪ How this happens, however, varies among the four different types of refrigeration systems. TYPES OF REFRIGERATION SYSTEMS 1. Vapor Compression Refrigeration Cycle  Mechanical compression is one method for removing heat from where it is not wanted and releasing it elsewhere.  The vast majority of domestic air conditioners utilize the mechanical compression refrigeration cycle to produce a cooling effect. C5S1_BUTILI2_MOD1 pg. 11   A mechanical compression refrigeration system cools by circulating a fluid through a sealed circuit of pipes or tubing.  A working fluid, called refrigerant, is used to absorb and expel heat. The most common include ammonia, Freon (and other chlorofluorocarbon refrigerants, aka CFCs), and HFC- 134a (a non-toxic hydrofluorocarbon).  The mechanical refrigeration cycle breaks down into four phases: compression, condensation, metering and evaporation. Heat flows into the evaporator and out of the condenser, making both coil types of heat exchangers. 2. Vapor Absorption Refrigeration Cycle  The vapor absorption refrigeration system comprises all the processes in the vapor compression refrigeration system like compression, condensation, expansion and evaporation.  In the vapor absorption system, the refrigerant used is ammonia, water or lithium bromide. The compressor is replaced with a generator and an absorber.  Simple Absorption System and How it Works?  The absorber is a vessel consisting of the weak solution of the refrigerant (ammonia in this case) and absorbent (water in this case).  When ammonia from the evaporator enters the absorber, it is absorbed by the absorbent due to which the pressure inside the absorber reduces further, leading to more flow of the refrigerant from the evaporator to the absorber.  At high temperature water absorbs lesser ammonia, hence it is cooled by the external coolant to increase its ammonia absorption capacity. The initial flow of the refrigerant from the evaporator to the absorber occurs because the vapor pressure of the refrigerant- absorbent in the absorber is lower than the vapor pressure of the refrigerant in the evaporator. C5S1_BUTILI2_MOD1 pg. 12  3. Evaporative Cooling Systems  Evaporative cooling does not use the traditional refrigeration cycle. Instead, these units cool warmer outdoor air by blowing it over water-soaked pads as it enters the home.  The water absorbs the heat from the air and evaporates. The cooler air is channeled into the home and the warm air out of it.  Water has an advantage of high volume heat capacity and much higher thermal conductivity compared to air.  Evaporative cooling systems depend on an internally or externally powered fan to draw air towards and blow air flow over the evaporative pad. Air must move into contact with the liquid to affect the cooling process.  Evaporative coolers can reduce air temperature by 5 to 9°C and are best suited for dry climates. They’re also less costly to install and more energy-efficient at times.  The designs vary either through larger containers, multiple fan orientations, various power and energy consumption classes of fans, many intake opening, placement and pattern variations and different materially manufactured evaporative pads (natural and synthetic).  All designs function under the same simple operating principle of water drips on vertical pad via pump mounted in a reservoir; an air circulation system that both draws air through an evaporative pad medium and redirect it out the cooler system.  Since evaporative coolers add moisture to the air and blow it around, they are sometimes known as "swamp coolers." C5S1_BUTILI2_MOD1 pg. 13  4. Thermoelectric Refrigeration  Thermoelectric refrigeration systems are unique from the three other types of refrigeration in that no refrigerant or water is used. These systems use an electric current and a thermocouple.  A thermocouple is made up of two different metal wires that are united at both ends. Insulation separates the rest of the wires from each other. When the current is directed on the thermocouple, one end will become hot and the other cool.  This type of refrigeration is generally used for small cooling loads that can be difficult to access, such as electronic systems. HEATING, VENTILATION, AND AIR CONDITIONING (HVAC) SYSTEM LOADS The field of heating, ventilation, and air conditioning – HVAC – is a science and practice of controlling indoor climate, thereby providing health and comfortable interior conditions for occupants in a well-designed, energy-efficient, and low emissions manner. HVAC ▪ The term “H” in HVAC stands for heating that comprises of any number of heating systems. ▪ The term “V” describes ventilation. This can be ventilating the facility using ductwork. It can also refer to combustion air. ▪ The term “AC” refers to air conditioning that comprises of 3 main methods – mechanical compression, vapor absorption and evaporative cooling. Air conditioners (direct expansion – DX systems) and chillers usually accomplish the job of air conditioning. The objectives of HVAC are: ▪ To control the temperature of air inside the designated “Air Conditioned" space ▪ To control air moisture ▪ To filter air and contain air borne particles C5S1_BUTILI2_MOD1 pg. 14  ▪ To supply outside fresh air for control of oxygen and carbon dioxide levels in the air conditioned space, and finally ▪ To control movement of air or draught. PROCESSES OF HVAC ▪ Heating: To increase the temperature by adding thermal energy to a space. ▪ Cooling: To decrease the temperature by removing thermal energy from a space. ▪ Humidifying: The process of increasing the relative humidity of a space by addition of water vapor or steam. ▪ Dehumidifying: The process of removing the water vapor or humidity of a space. ▪ Cleaning: The process of removing dust, pollens, smoke and contaminants from air inside the space. ▪ Ventilating: The process of adding external air to freshen up the air and maintaining gas ratio. ▪ Air Movement: To control the movement of the supplied air so that the inhabitants of the space do not feel discomfort. HVAC SYSTEMS UNITS AND RATINGS 1. Cooling Capacity  Defined as the heat load in a room that has to be removed in order to achieve a certain room temperature and humidity. The typical design is set to 24°C temperature and 55% Relative Humidity.  The amount of cooling needed by the space will be used to determine the capacity of the air conditioner needed. a. BTUh – “British Thermal Units per Hour”  It is a rate of heating or cooling expressed in terms of Btu per hour. (1kW = 3412 Btu)  1 BTU/hr is the amount of heat required to raise 1 pound of water by 1°F b. Ton of Cooling  One ton of cooling is the heat extraction rate of 12,000 Btu per hour.  Theoretically, it is energy required to melt one ton of ice in 24 hours. c. Ton of Refrigeration Effect  The cooling capacity of older Refrigeration units is often indicated in "tons of Refrigeration”. A ton of Refrigeration represents the heat energy absorbed when a ton (2000lb.) of ice melts during one 24-hour day.  The Btu equivalent of one ton of refrigeration is easy to calculate. Multiply the weight of one ton of ice (2000lb.) by the latent heat of fusion (melting) of ice (144 Btu/lb). Then divide by 24 hours to obtain Btu/hr.  One ton of Refrigeration effect = 2000 (lb) x 144 (Btu/lb) / 24 (hours) = 288,000 Btu / 24 hours = 12,000 Btu/hr C5S1_BUTILI2_MOD1 pg. 15   A refrigerating or air conditioning mechanism capable of absorbing heat can be rated in tons per 24 hours by its heat-absorbing ability (HA) in Btu divided by (24 hr x 12000 Btu = 288,000).  T = HA / 288,000  Where: T = tons of refrigeration effect; HA = heat-absorbing ability in Btu 2. COP – “Coefficient of Performance”  This coefficient is the ratio of the cooling capacity (W) as the output power (in form of removed heat load) versus power consumption (W) as the input power. COP = Cooling Capacity (W)/Power Consumption (W)  The higher the COP, the higher the efficiency of the air conditioner. Usually the value range from 2-4 but in recent years, the use of inverter compressors have enabled this coefficient to go higher than 4. 3. EER (Energy Efficiency Ratio)  This rating was established for manufacturers to rate their equipment so that consumers or consultants can tell the cooling efficiency of the air conditioner by just looking at the specifications provided.  The rating is obtained by dividing the cooling capacity (Btu/h) with the input power (Watt).  The larger the value of EER, the more efficient the air conditioner is. However, this rating does not give a complete picture of the efficiency of the unit. C5S1_BUTILI2_MOD1 pg. 16  4. SEER (Seasonal Energy Efficiency Ratio)  This ratio is more accurate as it takes into consideration non steady state conditions such as the start-up and shutdown cycles of the air-conditioner.  In choosing the SEER, the choice is always to go for a higher SEER as it is more efficient equipment. The trade-off in choosing a higher SEER is that usually the initial cost of the equipment will be higher. 5. Energy Star  This rating for an equipment shows that the equipment is designed to save energy hence reducing your electricity bills as well as protecting our environment. C5S1_BUTILI2_MOD1 pg. 17  3 HVAC SYSTEMS HVAC OPTIONS 1. Local systems ▪ Require no central equipment to perform their functions ▪ Components (air circulating fans/refrigerant compressor/condenser/cooling and heating coils) are contained within one box ▪ Normally appropriate for only very small load and/or small building/single room conditioning (restaurants, telephone exchanges, homes, small halls, etc.) a. Decentralized Systems (Individual Room Systems)  The window and split air conditioners are usually used for the small air conditioning capacities up to 5 tons. Window Units Mini-Split Cooling Units (ductless split units) b. Semi- centralized Systems (packaged systems)  Unitary packaged (one-piece systems) With Water-Cooled Condenser C5S1_BUTILI2_MOD1 pg. 18  With Air-Cooled Condenser c. Ducted split-type (two-piece systems)  The packaged air conditioners are available in the fixed rated capacities of 3, 5, 7, 10 and 15 tons. 2. Central Systems (Central Hydronic Systems) ▪ Require a full complement of central equipment (boilers, chillers, cooling towers, circulating pumps and similar equipment) and space for these equipment ▪ Need a distribution system to convey the heating and/or cooling medium to remote units HEAT CONVEYORS / MEDIA Another way to classify HVAC systems is by the media used to convey heat to and/or from the spaces served by the system. The three most commonly used in building applications are: ▪ Air ▪ Water ▪ Refrigerants – gases at normal temperatures and pressures, and must be compressed and condensed (liquefied) to be of service later as heat absorbers (examples, CFC, Freon, HCFC, etc.) C5S1_BUTILI2_MOD1 pg. 19 TYPICAL HVAC LAYOUT GENERATION EQUIPMENT ▪ Produces the heat (steam or hot water boilers, warm air furnaces and radiant panels) or cooling (chillers and cooling towers, and air-cooled compressors in packaged equipment). ▪ Packaged equipment (equipment that is self-contained, often all-electric) requires no central mechanical equipment.  Source of heating and cooling is contained within each piece of packaged HVAC equipment. ▪ Type of generation equipment can limit the choices available to the designer. ▪ Critical architectural decisions related to HVAC generation equipment are location, size, and service options of equipment rooms. DISTRIBUTION SYSTEM Method by which cooling and heating energy is "moved" throughout the building (hot/chilled water piping systems, or ductwork that distributes warm or cool air around the building). ▪ for packaged equipment systems, distribution is limited to a modest amount of ductwork (if any). ▪ limited by the capacity of the supply air fan provided as part of the packaged equipment. Larger central system distribution is powered by large central pumps and/or air-handling units. ▪ critical architectural decisions in distribution system design involve coordination with all other structure and services to eliminate conflicts and to provide for effective and efficient distribution of air and water throughout the building. ▪ critical junctures in a distribution system must be accessible for testing and balancing. TERMINAL EQUIPMENT Include devices that distribute conditioned air to the space (a diffuser is considered a terminal unit). ▪ either a separate or integral device is used to control the local space temperature (the "temperature control device"); both types are usually within reach of the occupant. ▪ in some systems, they are visible (as in the case of window air-conditioners or fan coil units, which act as both the terminal unit and temperature control device). C5S1_BUTILI2_MOD1 pg. 20  ▪ in other systems, they are concealed above the ceiling (a variable air volume box acts as the temperature control device, which controls the amount of air discharged from a number of ceiling diffusers, the terminal units). ▪ in a single zone system, there is no separate terminal control device. ▪ local diffuser is the "terminal unit," and a single thermostat sends control signals straight to the distribution equipment to maintain the set-point temperature for the entire area served by the single zone system. ▪ multiple single-zone air handlers achieve multiple zones of temperature control within the building. WINDOW AIR-CONDITIONING SYSTEMS ▪ The most widely used types of air conditioners and the simplest form of the air conditioning systems. ▪ Comprised of the rigid base on which all the parts of the window air conditioner are assembled. The base is assembled inside the casing which is fitted into the wall or the window of the room in which the air conditioner is fitted. ▪ Divided into two compartments: the room side, which is also the cooling side and the outdoor side from where the heat absorbed by the room air is liberated to the atmosphere. The room side and outdoor side are separated from each other by an insulated partition enclosed inside the window air conditioner assembly. ▪ The various parts of the window air conditioner can be divided into following categories: the refrigeration system, air circulation system, ventilation system, control system, and the electrical protection system. C5S1_BUTILI2_MOD1 pg. 21 SPLIT-TYPE AIR CONDITIONING SYSTEMS ▪ A split packaged unit consists of two separate pieces of equipment: an indoor air handler and an outdoor condensing unit. The indoor air handler is often installed in the fan room. Small air handlers can be ceiling hung. ▪ The condensing unit is usually located outdoors on a rooftop or podium or on the ground. ▪ A split packaged unit has its compressors and condenser in its outdoor condensing unit, whereas an indoor packaged unit usually has its compressors indoors. The cooling capacity of split packaged units varies from 3 to 75. ▪ The split-type air conditioning system comprises two parts:  The outdoor unit, fitted outside the room, houses components like the compressor, condenser, condenser cooling fan, and the expansion valve. The compressor is the maximum noise making part of the air conditioner, and since it is located outside the room, the major source of noise is eliminated.  The indoor unit is the unit that produces the cooling effect inside the room or the office. It comprises the evaporator or cooling coil, air filter, the cooling fan or blower, the drain pipe, and the louvers or fins.  After passing from the expansion coil, the chilled Freon fluid enters the cooling coil. The blower sucks the hot, humid and filtered air from the room and it blows it over the cooling coil.  As the air passes over cooling coil its temperature reduces drastically and also loses the excess moisture. The cool and dry air enters the room and maintains comfortable conditions of around 18-27° Celsius as per the requirements. ▪ For this unit, there is no need for any slot in the wall of the room. Further, present day split units have aesthetic appeal and do not take up as much space as a window unit. ▪ A split air conditioner can be used to cool one or two rooms. ▪ The window and split air conditioners are usually used for the small air conditioning capacities up to 5 tons. Ducted Split-Type Packaged System C5S1_BUTILI2_MOD1 pg. 22 PACKAGED AIR CONDITIONING SYSTEM ▪ In this system, the important components of the air conditioners are enclosed in a single casing like window AC. Thus, the compressor, cooling coil, air handling unit and the air filter are all housed in a single casing and assembled at the factory location. ▪ Depending on the type of the cooling system used in these systems, the packaged air conditioners are divided into two types: ones with water-cooled condenser and the ones with air- cooled condensers. C5S1_BUTILI2_MOD1 pg. 23  ▪ The packaged air conditioners are available in the fixed rated capacities of 3, 5, 7, 10 and 15 tons. These units are used commonly in places like restaurants, telephone exchanges, homes, small halls, etc. Packaged Air Conditioners with Water-Cooled Condenser ▪ The condenser, of shell and tube type, is cooled by the water with refrigerant flowing along the tube side and the cooling water flowing along the shell side.  The water has to be supplied continuously in these systems to maintain functioning of the air conditioning system. ▪ The shell and tube type of condenser is compact in shape and it is enclosed in a single casing along with the compressor, expansion valve, and the air handling unit including the cooling coil or the evaporator.  This whole packaged air conditioning unit externally looks like a box with the control panel located externally. ▪ In the packaged units with the water-cooled condenser, the compressor is located at the bottom along with the condenser.  Above these components the evaporator or the cooling coil is located. ▪ The air handling unit comprising of the centrifugal blower and the air filter is located above the cooling coil. From the top of the package air conditioners, the duct comes out that extends to the various rooms that are to be cooled. C5S1_BUTILI2_MOD1 pg. 24 Packaged Air Conditioners with Air-Cooled Condensers ▪ The condenser of the refrigeration system is cooled by the atmospheric air. There is an outdoor unit that comprises of the important components like the compressor, condenser and in some cases the expansion valve. ▪ The outdoor unit can be kept on the terrace or any other open place where the free flow of the atmospheric air is available. The fan located inside this unit sucks the outside air and blows it over the condenser coil cooling it in the process. The condenser coil is made up of several turns of the copper tubing and it is finned externally. ▪ The packaged ACs with the air cooled condensers are used more commonly than the ones with water cooled condensers since air is freely available and it is difficult to maintain continuous flow of the water. ▪ The cooling unit comprising of the expansion valve, evaporator, the air handling blower and the filter are located on the floor or hanged to the ceiling. The ducts coming from the cooling unit are connected to the various rooms that are to be cooled. C5S1_BUTILI2_MOD1 pg. 25 CENTRALIZED AIR-CONDITIONING SYSTEMS ▪ Central air conditioning plants are used for applications like big hotels, large buildings having multiple floors, hospitals, etc., where very high cooling loads are required. ▪ The central air conditioning plants or the systems are used for large buildings, hotels, theaters, airports, shopping malls etc. ▪ In the central air conditioning systems there is a plant room where large compressor, condenser, thermostatic expansion valve and the evaporator are kept in the large plant room. They perform all the functions similar to a typical refrigeration system. However, all these parts are larger in size and have higher capacities. ▪ The compressor is of several types - reciprocating, rotating screw, centrifugal, scroll - with multiple cylinders and is cooled by water like a car engine. The compressor and the condenser are of shell and tube type. While the small air conditioning system uses capillary expansion valve, the central air conditioning systems use thermostatic expansion valve. ▪ The chilled air is passed via the ducts to all the rooms, halls and other spaces that are to be air- conditioned. Thus, there is only the duct passing the chilled air in all the rooms and there are no individual cooling coils, and other parts of the refrigeration system in the rooms. What we get is the completely silent and highly effective air conditioning system in the rooms. ▪ The amount of chilled air that is needed in the room can be controlled by the openings depending on the total heat load inside the room. HVAC SYSTEM REQUIREMENTS Primary Equipment includes ▪ Heating equipment such as steam boilers and hot water boilers to heat buildings or spaces, ▪ Air delivery equipment as packaged equipment to deliver conditioned ventilation air by using centrifugal fans, axial fans, and plug or plenum fans, and ▪ Refrigeration equipment that delivers cooled or conditioned air into space. It includes cooling coils based on water from water chillers or refrigerants from a refrigeration process. C5S1_BUTILI2_MOD1 pg. 26 Space requirement is essential in shaping an HVAC system to be central or local. It requires five facilities as the following: ▪ Equipment rooms: since the total mechanical and electrical space requirements range between 4 and 9% of the gross building area. It is preferable to be centrally located in the building to reduce the long duct, pipe, and conduit runs and sizes, to simplify shaft layouts, and centralized maintenance and operation. ▪ HVAC facilities: heating equipment and refrigeration equipment require many facilities to perform their primary tasks of heating and cooling the building. The heating equipment requires boiler units, pumps, heat exchangers, pressure-reducing equipment, control air compressors, and miscellaneous equipment, while the refrigeration equipment requires water chillers or cooling water towers for large buildings, condenser water pumps, heat exchangers, air- conditioning equipment, control air compressors, and miscellaneous equipment. ▪ Fan rooms contain the HVAC fan equipment and other miscellaneous equipment. The rooms should consider the size of the installation and removal of fan shafts and coils, the replacement, and maintenance. The size of fans depends on the required air flow rate to condition the building, and it can be centralized or localized based on the availability, location, and cost. It is preferable to have easy access to outdoor air. ▪ Vertical shaft: provide space for air distribution and water and steam pipe distribution. The air distribution contains HVAC supply air, exhaust air, and return air ductwork. Pipe distribution includes hot water, chilled water, condenser water, and steam supply, and condenser return. The vertical shaft includes other mechanical and electrical distribution to serve the entire building including plumbing pipes, fire protection pipes, and electric conduits/closets. ▪ Equipment access: the equipment room must allow the movement of large, heavy equipment during the installation, replacement, and maintenance. Air distribution considers ductwork that delivers the conditioned air to the desired area in a direct, quiet, and economical way as possible. Air distribution includes: ▪ air terminal units such as grilles and diffusers to deliver supply air into a space at low velocity; ▪ fan-powered terminal units, which uses an integral fan to ensure the supply air to the space; ▪ variable air volume terminal units, which deliver variable amount of air into the space; ▪ all-air induction terminal units, which controls the primary air, induces return air, and distributes the mixed air into a space; ▪ and air-water induction terminal units, which contains a coil in the induction air stream. All the ductwork and piping should be insulated to prevent heat loss and save building energy. It is also recommended that buildings should have enough ceiling spaces to host ductwork in the suspended ceiling and floor slab, and can be used as a return air plenum to reduce the return ductwork. The piping system is used to deliver refrigerant, hot water, cooled water, steam, gas, and condensate to and from HVAC equipment in a direct, quiet and affordable way. ▪ Piping systems can be divided into two parts: the piping in the central plant equipment room and the delivery piping. ▪ HVAC piping may or may not be insulated based on existing code criteria. C5S1_BUTILI2_MOD1 pg. 27  4 CENTRALIZED HVAC SYSTEMS Local Semi- De-Centralized Centralized Window Mini Split-Type Unitary Split-Type Ductless Air-Cooled Water-Cooled EQUIPMENT TO GENERATE HEATING OR COOLING Heating Systems Main Equipment Cooling Systems Main Equipment The main equipment used in heating systems The main equipment used in cooling systems include: include: ▪ Furnace ▪ Chillers & Compressors ▪ Hot Water & Steam Boiler ▪ Cooling Towers ▪ Heat Pump ▪ Air Handling Units & Fan Coil Units ▪ Local heating Systems CHILLERS ▪ Chillers are the primary piece of equipment in a central cooling system. These devices remove the heat gathered by the re-circulating chilled water system as it cools the building. Selection depends on the fuel source and the total cooling load. ▪ Two principal types; air-cooled and water cooled. Compared to water, air is a poor conductor of heat and therefore air-cooled chillers are larger and less efficient.  Air cooled chillers are generally located outside the building and reject heat directly to the atmosphere, while  Water cooled chillers are generally located within the building and use cooling towers located outside the building to reject the heat. ▪ They are usually classified by the type of compressor used to drive the refrigeration cycle. C5S1_BUTILI2_MOD1 pg. 28  Air-Cooled Chillers Water-Cooled Chillers Air-Cooled Water-Cooled C5S1_BUTILI2_MOD1 pg. 29 COMPRESSORS Reciprocating Compressors ▪ They use a proven technology and generally have a lower initial cost than other chiller types. ▪ They produce more vibration and for this reason, care must be exercised in mounting, particularly if used on a rooftop. ▪ Reciprocating compressors are usually used in smaller systems up to 100 tons and are typically more efficient than centrifugal units. Rotating Screw Compressors ▪ Screw compressors are made up of two threaded inter-fitting rotors (screws) that are coupled together to compress the volume occupied by the gas (refrigerant). ▪ The refrigeration capacity of twin-screw compressors is 50 to 1500 tons but is normally used in the 200 tons to 800 tons range. Centrifugal Compressors ▪ Centrifugal compressors are made up of a rotor located inside a special chamber. ▪ The centrifugal compressor is ideal for air conditioning applications because it is suitable for variable loads, has few moving parts, and is economical to operate. ▪ The available refrigeration capacity for centrifugal compressors ranges from 100 to 2,000 tons, making them applicable for large central plants. Scroll Compressors ▪ Scroll compressors generally have smaller capacities than many other types and are becoming popular in residential equipment. ▪ Have fewer parts, thus, less maintenance concerns, have smoother, quieter operations, and can operate under dirtier conditions. ▪ The refrigeration capacity of currently manufactured scroll compressors is 60 tons. HEAT REJECTION EQUIPMENT ▪ With chillers, there must be a way to reject the heat that is removed from the re-circulating chilled water system. Reject heat is handled by the condensing water system which serves the condensing process within the refrigeration cycles. For large buildings, this requirement is satisfied by a cooling tower. C5S1_BUTILI2_MOD1 pg. 30  ▪ The purpose of heat rejection equipment in an air- conditioning system is to provide a heat transfer means to reject all the heat from the air-conditioning system. This heat includes the heat absorbed by the evaporator from the space plus the heat of the energy input into the compressor. ▪ Three common types of heat rejection equipment:  Air-cooled  Water-cooled  Evaporative COOLING TOWER ▪ A cooling tower is a heat rejection device, installed outside of the building envelope, through which condenser water is circulated. ▪ Refrigerant in the refrigeration cycle is condensed in a refrigerant-to-water heat exchanger. Heat rejected from the refrigerant increases the temperature of the condenser water, which must be cooled to permit the cycle to continue. ▪ The condenser water is circulated to the cooling tower where evaporative cooling causes heat to be removed from the water and added to the outside air. ▪ The cooled condenser water is then piped back to the condenser of the chiller. ▪ Floor space requirement are 0.20% of the building gross floor area (for towers up to 2.40m high) and 0.30% of the building GFA for towers above 2.40m high. Forced Draft Tower ▪ In forced draft cooling towers, air is "pushed" through the tower from an inlet to an exhaust. A forced draft mechanical draft tower is a blow-through arrangement, where a blower type fan at the intake forces air through the tower. C5S1_BUTILI2_MOD1 pg. 31 Induced Draft Tower ▪ A second type of tower, induced draft has a fan in the wet air stream to draw air through the fill. The fan located is located at the discharge end, which pulls air through tower. Natural Draft Tower ▪ Natural draft tower has no mechanical means to create airflow. Natural-draft cooling towers use the buoyancy of the exhaust air rising in a tall chimney to provide the draft. Warm, moist air naturally rises due to the density differential to the dry, cooler outside air. AIR HANDLING UNITS & FAN COIL UNITS An air handling system is a means of providing conditioned air to the space in order to maintain the environmental requirements. ▪ There are two types of air-handling equipment: refrigerant type (considered air-conditioning units) and chilled water type (called air-handling units). ▪ An air-conditioning unit is typically factory-assembled with refrigerant-type cooling and electric, steam or hot water heating. ▪ Air-handling units are usually a semi-custom type of air-handling device that can be factory- assembled, field-assembled, or a combination of both. ▪ Air-handling units typically use electric, steam or hot water for heating medium ▪ Sufficient space is required around the system to allow for proper maintenance. ▪ AHUs can bring in outside air and heat or cool it; they are more common in large buildings with a centralized HVAC system. C5S1_BUTILI2_MOD1 pg. 32 FAN COIL UNIT (FCU) ▪ A fan-coil unit is a small-scale air handling unit with circulation fan, cooling and/or heating coil, filter, and appropriate controls. It is essentially a terminal device because it serves only one room or a small group of rooms. ▪ Fan-coil control is typically achieved through control of water flow through the coil using a control signal from the zone thermostat. Occupants can usually adjust supply air louvers to provide some control over air distribution patterns. ▪ A fan-coil system requires filter changes and maintenance of fans and coils. Fan noise may be a concern in some critical occupancies. ▪ It is most commonly used in hotels, condominiums, and apartments. AIR DISTRIBUTION OUTLETS ▪ Ceiling diffuser – the most common air outlet. They have either radial or directional discharge which is parallel to the mounted surface. Some typical applications are spot heating or cooling, large capacity, mounting on exposed ductwork, horizontal distribution along a ceiling, and perimeter air distribution. They come in various shapes and sizes: round, rectangular, square, perforated face, louver face, modular type. C5S1_BUTILI2_MOD1 pg. 33  ▪ Linear slot outlets - long narrow air supply device with an air distribution slot between 12-25mm in length. Various types are linear bar, T-bar slot, linear slot, and light diffuser. Some applications are high sidewall installation with flow perpendicular to the mounting surface, high sidewall installation with 15-30 degree upward/downward directional adjustability, perimeter ceiling installation, sill installations, and floor installations. ▪ Grille – a supply air outlet that consists of a frame enclosing a set of vanes which can be mounted vertically, horizontally or in both directions. A grille combined with a volume control damper is called a register. Grilles mounted on the ceiling and discharging down are unacceptable. Ceiling installation would require a special grille with curved vanes to discharge the air parallel to the mounting surface. PUMPS ▪ The 4 most common types of HVAC centrifugal pumps are end-suction, horizontal or vertical split- case, in-line mounted, and vertical. The configuration of the pump shaft determines if the pump is a horizontal or vertical pump. Pumps may be arranged in various configurations to provide the design flow and economical operation at partial flow or for system backup. FANS ▪ Fans are available in a variety of impeller or wheel design and housing design. These variables affect the performance characteristics and applications for each individual type of fan. The most common fan designs used in HVAC systems are centrifugal and axial. TYPES OF CENTRAL AIR CONDITIONING SYSTEMS ACCORDING TO COOLING SYSTEMS Direct Expansion Central Air-Conditioning C5S1_BUTILI2_MOD1 pg. 34 Chilled Water Central Air Conditioning Plant This type of system is more useful for large buildings comprising of a number of floors. TYPES OF CENTRAL AIR CONDITIONING SYSTEMS ACCORDING TO HEAT TRANSFER MEDIUM Centralized Ducted “All–Air” Systems ▪ These are systems in which the primary movement of heat around the building is via heated and cooled air. ▪ These systems are the most common in large spaces such as office buildings, common public areas, retail, shopping, manufacturing areas, airports, hotel lobbies etc. ▪ In an ‘All-Air system’, the refrigerant or chilled water is used to cool and dehumidify the air in the air handling unit (AHU). The cool air is then circulated throughout the building thru the ductwork. Heating can also be accomplished either by hot water or electrical strip heaters. ▪ The centralization of these systems require either a mechanical room adjacent to the controlled space for locating the AHU and large ductwork in building space. ▪ Fresh outside air is drawn into the building through the intake louver, mixed with return air, heated or cooled to a controlled temperature, circulated around the building and provided to the occupied space. Exhaust air is extracted from the space and dumped to the outside. In general, the majority of the return air is recycled via the return air duct. ▪ All-air systems offer excellent control of interior air quality. The central air-handling equipment can be designed for precise control of fresh air, filtration, humidification, dehumidification, heating, and cooling. C5S1_BUTILI2_MOD1 pg. 35  ▪ “All-air” systems are usually described by 2 variables: the type of air-handling unit provided (constant volume/reheat or variable volume/cooling only), and the type of terminal control device used (constant air volume/variable air temperature or variable air volume/constant air temperature) to control local zone comfort conditions.  Constant-volume systems operate at a constant airflow rate; only temperature varies to maintain the zone set point.  Variable air volume (VAV) systems use variable volume terminal units or boxes to vary the airflow in each zone or space in accordance to the thermostat signals within the space. Centralized Fluid-Based Hydronic Systems ▪ An all-water hydronic system typically use terminal units, such as fan-coil units or unit ventilators, to provide the local temperature control. When heating, the terminal units draw heat from the water and when cooling these reject heat to the water. ▪ Hot and chilled water piping systems are the primary distribution system, so ductwork is eliminated and making all-water systems the most compact of all. ▪ The biggest drawback of all-water hydronic system is the difficulty in providing adequate indoor air quality. These systems are fairly common in office rooms, hotel rooms, schools, building perimeter control etc. C5S1_BUTILI2_MOD1 pg. 36 Combined (Hybrid) Water and Air Systems ▪ Hybrid systems use both air and water (cooled or heated in central plant room) distribution to room terminals to perform cooling or heating function. Unlike all-water system, this system ensures ventilation air in the spaces so that indoor air quality is not sacrificed. ▪ The most critical performance issue facing an all-water fan-coil system is ventilation air. Fan coils installed in interior zones can not easily provide such outdoor air ventilation. An air-water fan-coil system can overcome this constraint. ▪ Improved air quality and humidity control is provided, since a central ventilation system air handler can be used to provide better outside air filtration, better control of relative humidity, and an opportunity to recover waste heat from building exhaust airstreams. ▪ Found in high-rise buildings where a minimum amount of ductwork is desirable. C5S1_BUTILI2_MOD1 pg. 37 HVAC SPACE PLANNING ▪ Space required to house HVAC equipment and associated pipe and duct shafts can amount to 10% of the building floor area, depending on the building application and type of HVAC system used. The first step in planning the HVAC system layout is to identify the location and configuration of the central equipment. In large buildings using central systems, this often includes 3 types of equipment rooms:  A central plant equipment space (usually one location in the building housing central chillers, boilers, and related equipment  A rooftop location for cooling towers  Equipment room/s for large central air-handling units ▪ Central plant equipment rooms are often located at the top of a building to:  Minimize the piping distance to connect the chillers to the rooftop cooling towers  Minimize the length of expensive boiler flues that typically extend well above rooftop heights  May also be located on the lowest floor of the building  Or the boilers and chillers may be located in two different locations CENTRAL EQUIPMENT ROOM PLANNING ▪ Central equipment rooms should have between 3600-4200mm clear height available from the finished floor to the soffit of the structure to allow for adequate clearance above the main equipment for accessories and large piping crossovers. ▪ Long narrow rooms with a ratio of 1:2 (width to length) usually allow for the most flexible and efficient layout of the equipment. ▪ Equipment such as chillers and shell-and-tube heat exchangers require clear space equal to the length of the equipment in order to pull the heat exchange tubes for servicing. ▪ Provide proper vibration isolation for large equipment, particularly rotating equipment, such as chillers and pumps ▪ Access to equipment rooms is an important consideration. Adequate doors and routes to freight elevators and/or to the building exterior should be planned such that the largest piece of equipment can be easily installed and possibly removed for servicing in the future AIR-HANDLING EQUIPMENT ROOM PLANNING ▪ The number and location of central air-handling unit equipment rooms (commonly called fan rooms) are critical to a successful HVAC system. ▪ Once the number of AHUs is determined, the next decision is how or whether they are to be grouped together in separate rooms. The following summarizes typical AHU room arrangement approaches:  Scattered or separated units – often used in low-rise buildings employing rooftop equipment  Air handlers are simply located as centrally as possible to the separate zones they serve (and are thus scattered throughout the building as a function of its separate zones)  Results in the most efficient duct sizing and minimal duct sizes  Because air handlers will be located directly above occupied spaces, noise and vibration isolation are critical factors C5S1_BUTILI2_MOD1 pg. 38   Central core placement – most efficient layout and duct distribution layout  All air handling unit rooms are located together near the building core, often on multiple floors in high-rise buildings  Tends to yield the most efficient layout and duct distribution layout if one air handler can serve an entire floor  Horizontal or vertical ducting is required to admit and reject fresh outside air and to exhaust spent air  Air handling unit rooms placed in the central core can take advantage of other service elements such as elevator shafts and restrooms to buffer noise  No equipment room wall should be located immediately adjacent to an occupied space, and equipment rooms are best stacked vertically to minimize piping and airshaft requirements  At least 2 and preferably 3 sides of the equipment room are free of vertical obstructions so that supply and return ductwork can pass through them to serve the occupied areas  Perimeter rooms – minimizes ducting required for outside air and exhaust air  Can reduce the efficiency of the supply/return duct system, unless multiple units are required for each floor  Potential lost use of premium perimeter floor areas  Potential negative aesthetic impact of large intake/exhaust louvers on the exterior  Proximity of potentially noisy equipment close to occupied areas of the building  Detached rooms – moves the equipment room outside the main building requiring an adjacent protruding service shaft  Sometimes allow for maximum space utilization and flexibility within the main floor plate of the building they serve C5S1_BUTILI2_MOD1 pg. 39