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    Hvac Basics Pdf

    HVAC - A Beginner's Guide - Free download as PDF File .pdf), Text File .txt) or The basic purpose of having an HVAC system at homes and theatres will be. The goal of the heating, ventilating, and air conditioning (HVAC) system is to create and that any HVAC system can be dissected into basic subsystems. These. Be familiar with Basic HVAC terminology. • Understand the fundamentals of the refrigeration cycle. • Know the four major components of an HVAC system and be .

    The system refrigerant starts its cycle in a gaseous state. The compressor pumps the refrigerant gas up to a high pressure and temperature. From there it enters a heat exchanger sometimes called a condensing coil or condenser where it loses energy heat to the outside, cools, and condenses into its liquid phase. An expansion valve also called metering device regulates the refrigerant liquid to flow at the proper rate. The liquid refrigerant is returned to another heat exchanger where it is allowed to evaporate, hence the heat exchanger is often called an evaporating coil or evaporator. As the liquid refrigerant evaporates it absorbs energy heat from the inside air, returns to the compressor, and repeats the cycle. In the process, heat is absorbed from indoors and transferred outdoors, resulting in cooling of the building. In variable climates, the system may include a reversing valve that switches from heating in winter to cooling in summer. By reversing the flow of refrigerant, the heat pump refrigeration cycle is changed from cooling to heating or vice versa. This allows a facility to be heated and cooled by a single piece of equipment by the same means, and with the same hardware. Main article: Free cooling Free cooling systems can have very high efficiencies, and are sometimes combined with seasonal thermal energy storage so that the cold of winter can be used for summer air conditioning. Common storage mediums are deep aquifers or a natural underground rock mass accessed via a cluster of small-diameter, heat-exchanger-equipped boreholes. Some systems with small storages are hybrids, using free cooling early in the cooling season, and later employing a heat pump to chill the circulation coming from the storage. The heat pump is added-in because the storage acts as a heat sink when the system is in cooling as opposed to charging mode, causing the temperature to gradually increase during the cooling season. Some systems include an "economizer mode", which is sometimes called a "free-cooling mode".

    The air is ventilated by maintaining the gas ratio which can be done by adding external fresh air. Lastly, the system controls the air movement that is supplied in a space which ensures that those in the place are comfortable. The following are the basic components of an HVAC system and the role they play to keep the condition the suitable; Furnace This is the largest and the main component of the commercial HVAC system.

    It heats the air that is supplied the system; this can be done through the heat pump, solar energy, or the burning of the natural gasses. Inside the furnace, there is a heat exchanger which helps to switch on when the furnace is activated.

    It pulls the cold air and heats and circulates the air out through the vents. Thermostat The thermostat can either be set manually or programmed in advance to the desired temperature.

    It is easily visible and accessible part of the system. The thermostat can trigger the heat exchanger or evaporator coil-condensing unit to circulate a space with cold or warmed air. Evaporator Coil This helps to cool the heated air. It is connected to the condensing unit which is filled with refrigerant gas.

    The unit is usually installed outside the room. It pumps the condensed liquid to the evaporator coil which is evaporated to gas again. Each chiller has its own Ch e r evaporator, compressors, condenser and expansion components.

    In other words an expanded room air-conditioner, expanded multifold times. The water used in a chiller system is DM demineralized water. The only difference is that the capacity of the compressor is much more. This Chilled water which is at a temperature of 5. Hence in a chiller system the refrigerant does not directly cool the warm area. The above diagram shows 3 chillers. The primary pumps are used to pump the water into the chillers. Depending upon the amount of cooling required the compressors in each chiller is switched on or off.

    The secondary pumps pump the cool water coming out of the chillers into the cooling coils of the various AHUs present in the building. There are basically 2 types chilled water distribution. In case of constant flow a constant amount of chilled water is sent from the chillers into the cooling coils of the AHU.

    Just remove the secondary pumps in the above sketch and you have a constant flow system. In case of variable flow system,. The refrigerant in the chiller is either air-cooled or water-cooled. In case of water-cooled chillers the cooling tower is used to cool the water which cools the refrigerant. The cooling tower has fans. There is make-up water available to make up for any loss of water.

    Water Cooled Chiller:. A measure of the load condition is the difference between the supply and return header temperatures. By measuring this difference, the load can be determined and energy saving means adopted, as will be illustrated below: If there is only one chiller, the microprocessor of the chiller will receive inputs of the supply and return header temperatures, apart from safety interlocks like water flow, refrigerant pressures etc and based on the difference, a decision on how many compressors can be switched on will be determined.

    Let us take the case of 2 chillers, each with its own microprocessor panel. This is because the microprocessor of chiller 1 will not know that there is another microprocessor panel of chiller 2 next to it. Assuming no BMS or any other controls from Chiller manufacturer. Each chiller will switch off one compressor, as both the chillers have received same supply and return header temperature input.

    Please Note: Whether BMS is there or not, the chiller manufacturer will use temperature sensors in supply and return line of the chiller as inputs to the microprocessor. Coming back to our above example: Also, one chilled water pump can also be shut down. The same example can be extended to more number of chillers.

    Please note: The decision to run the compressors of the chiller is taken by the micrprocessor panel of Chiller and not by BMS. BMS will only decide whether one or more chillers need to run. The operating of the compressors of the chiller, is referred to in HVAC industry, as loading and unloading of the chiller.

    While switching off the chiller, The chiller is first switched off, then primary pumps and then the butterfly valve is closed. When again switching on the chiller the reverse sequence is followed.

    Aiir Handlliing Uniitt:: The filter in the AHU filters the dust particles in the air from the return air A r Hand ng Un duct and fresh air supply. This air then passes across a cooling coil inside which cold water is running from the chiller, through the pumps. Heat exchange occurs between the air and the chilled water in the cooling coil. The cooled air is then circulated into the supply air duct by means of a fan. Using ducts this cooled air is distributed to the various areas where this AHU is catering to.

    A differential pressure switch connected across the filter is used to give a digital output when the filter is clogged. A differential pressure switch is used to monitor the functioning of the fan The AHU can also be operated on time schedule basis. For e. The AHU can be switched on from 9. The return air temperature of each AHU is used to monitor the opening and closing of the valve.

    If the return air temperature is high then the valve is opened wide. If the return air temperature is low, then the valve is closed allowing only little water flow. Variiablle Aiir Vollu me Uniitts:: The air enters each room via a damper system. Each zone will have varying temperature and pressure requirements.

    This requirement is met by varying the closing and opening of the damper which in turn controls the amount of cool air flowing into the zone. The VAVs are similar to the taps in each of the rooms.

    Glossary of HVAC terms - Wikipedia

    The water available in the overhead tank can be used in the rooms as per each rooms requirement by variably opening and closing the taps. This temperature is monitored while using VAV. If the pressure is too high a Variable frequency drive is used to lower the speed of the AHU fan.

    Re duciing RH off a room: In pharma and textile industries a specific RH has to be maintained.

    HVAC - A Beginner's Guide

    To reduce RH we increase the cooling. Increased cooling leads to dehumidification. Due to dehumidification the water content in the air reduces.

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    Thus the RH of the room is reduced. After this process if the temperature of the room has to be increased a little then we can switch on the heater. G ossary Humidity: It is the measure of moisture content in a substance.

    Air always exists in the form of a mixture of dry air and water vapour. Relative Humidity: The ratio of the actual moisture content of air at a given condition to the moisture condition that would have been present at saturated conditions for the same temperature.

    Dew point temperature: It is the temperature at which air can no longer hold the moisture and when condensation commences. Boiling point: We can alter the boiling points of liquids by changing the pressure.

    When pressure increases the boiling point increases. In other words the temperature of the liquid increases when we increase the pressure. Anamolous Expansion of water: Between 0 deg centigrade and 4 deg centigrade water actually contracts. Hence care should be taken that the water flowing in chiller never reaches this temperature. Heat Exchange: Exchange of heat happens from a higher temperature area to a lower temperature area. The abbreviation for British thermal units.

    The amount of heat required to raise one pound of water to one degree Fahrenheit per hour, a common measure of heat transfer rate. Tonnage TR: The unit of measure used in air conditioning to describe the cooling capacity of a system.

    Glossary of HVAC terms

    One ton of cooling is based on the amount of heat needed to melt one ton lbs. Fresh Air: Outdoor air introduced into HVAC system. Heating, Ventilation, and Air Conditioning - Microcontrollers, sensors, and monitoting.

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