HVAC By Osama Hantash 201610123 What is HVAC ? HVAC stands for Heating, Ventilation, and Air Conditioning. An HVAC System is the equipment technology, and processes that go into heating, cooling and ventilating a commercial or residential property, Its goal is to provide thermal comfort and acceptable indoor air quality, HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics and heat transfer. HVAC systems can be classified into central and local systems according to multiple zones, location, and distribution. Main Goals Of HVAC Systems Controlling the Temperature Fresh Air Circulation Air Filtration Efficient and Economic Quiet and Unobtrusive HVAC System Types Central HVAC systems locate away from buildings in a central equipment room and deliver the conditioned air by a delivery ductwork system. Central HVAC systems contain all- air, air-water, all-water systems. Two systems should be considered as central such as heating and cooling panels and water-source heat pumps. HVAC System Types Local HVAC systems can be located inside a conditioned zone or adjacent to it and no requirement for ductwork. Local systems include local heating, local air-conditioning, local ventilation, and split systems. How does HVAC work In most cases, central air conditioning refers to either a split-system air conditioner or a heat pump, which both have an outdoor and indoor unit. The indoor and outdoor units work together to distribute cool air through a system of ducts in your home. Together, they are composed of five main parts: a thermostat (thermometer), an outdoor unit, an indoor unit, tubes that connect the outdoor and indoor units, and ductwork throughout the home. While a split-system AC only cools, a heat pump can reverse the flow of refrigerant to heat the home, so the process works in reverse. HVAC System types based on functionality SPLIT UNIT DX SYSTEMS VRF HVAC SYSTEMS PACKAGE UNITS CHILLED WATER SYSTEM Main Difference Between Chillers and DX systems The immediate and most noteworthy difference between these two units is that the DX (direct expansion) unit cools air, and chiller units' cool water. DX Units vary in use between supplemental or emergency building AC, or primary AC at tented events or relief structures. Chiller units' cool water for use in other AC systems like chilled water air handlers. Split Unit Systems An HVAC split system is for homes that have space for large indoor cabinets. The split system model holds the condenser and compressor in an outdoor cabinet. Another indoor cabinet will hold the evaporator coil, and an air handler sends the cool air through the duct system. A line set - a copper tube that connects both the indoor and outdoor components - moves cold air to the house. Basic HVAC Cycle Thermostat A Thermostat is a device that monitors the indoor temperature and automatically adjusts your heating or cooling system to maintain the desired level. Thermostats types come in: 1) Non-Programmable Thermostat 2) Programmable Thermostat 3) Wi-Fi Thermostat 4) Smart Thermostat Outdoor Unit Components In outdoor unit lots of heat is generated inside the compressor and the condenser, hence there should be sufficient flow of the air around it. The outdoor unit is usually installed at the height above the height of the indoor unit inside the room though in many cases the outdoor is also installed at level below the indoor unit. The Evaporator Coil The evaporator coil plays a starring role in keeping your home cool and comfortable. Lined with thin aluminum fins, the evaporator coil looks and functions almost like a car’s radiator except that it absorbs heat instead of rejecting it. As cold refrigerant enters the evaporator coil, it also draws latent heat from the air passing through the coil. The capture of this heat energy transforms the refrigerant from a cold mist to a warm vapor. Meanwhile, the air that passes through the evaporator coil loses its warmth and moisture, resulting in the cool, dry air, these coils are mostly shielded from dust and debris thanks to the HVAC air filter. Compressor The Compressor is most important part of the any air conditioner. It compresses the refrigerant and increases its pressure before sending it to the condenser. The size of the compressor varies depending on the desired air conditioning load. External power must be supplied to the compressor, which is utilized for compressing the refrigerant and during this process lots of heat is generated in the compressor, which must be removed by some means. Condenser Just like the evaporator coil, the condenser coil also plays an important role in your central air conditioner’s operation. Unlike the evaporator coil, however, the condenser coil’s job is to release heat from the refrigerant. Think of your car’s radiator and how it’s designed to help dissipate heat from the coolant circulating inside. A condenser fan built into the outdoor cabinet directs ambient air through the condenser coil like how the indoor air handler’s built-in fan directs air through the condenser coil. But instead of absorbing latent heat, the condenser coil uses the air flow to expel heat from the refrigerant. This process changes the refrigerant from hot, highpressure vapor into a hot liquid. Before the refrigerant can be reused in the refrigerant cycle, there’s one more important component it must go through. The Expansion Valve In order to complete the air conditioning process, the refrigerant needs to be transformed back into a cold mist, the expansion valve essentially converts the flow of liquid refrigerant back into vapor form. The liquid refrigerant enters the valve through an extremely narrow orifice designed to meter the amount of refrigerant that passes through. As the liquid refrigerant passes through the orifice, the refrigerant experiences a significant reduction in pressure. The resulting drop in pressure also causes the refrigerant to expand into a mist form. The rapid expansion also throws off a great deal of heat energy, rapidly cooling the refrigerant in the process. The result is refrigerant that’s returned to its cold mist form in preparation for its trip through the evaporator coil. Indoor Unit Components Heat Exchanger Decorative Cover Air Inlet Air Outlet Air Filter Fan Display Section Split Unit Advantages: 1. These Ac’s have low initial costs 2. Easy to install 3. No Duckwork required 4. Each System can be controlled separately Disadvantages: 1. Distance between indoor and outdoor units shouldn’t exceed 150ft otherwise performance will be affected 2. Limited air flow VRF Systems variable refrigerant volume (VRV), is an HVAC technology invented in 1982, Like ductless split units, VRFs use refrigerant as the cooling and heating medium. This refrigerant is conditioned by one or more condensing units (which may be outdoors or indoors, water or air cooled), and is circulated within the building to multiple indoor units. VRF systems, unlike conventional chiller-based systems, allow for varying degrees of cooling in more specific areas (because there are no large air handlers, only smaller indoor units), may supply hot water in a heat recovery configuration without affecting efficiency, and switch to heating mode (heat pump) during winter without additional equipment, all of which may allow for reduced energy consumption. How Does a VRF System Work? Variable refrigerant flow systems continually adjust the flow of refrigerant to each indoor evaporator. Thus, each indoor evaporator has its own set of controls, allowing for air conditioning in a server room, for instance, and heating in an office space to occur simultaneously, with one HVAC system. The indoor units link to the outdoor unit via control wires. The outdoor unit responds to the heating or cooling demand from the indoor units by manipulating its compressor speed to match the total requirements. VRF System VRF Systems Advantages Energy Saving can reach up to 40% High COP Less Noise Space saving Precise temperature control Zoned comfort • • • • • • Disadvantages • • • • High initial cost (due to backup units) Refrigerated piping Environmental concerns Separate ventilation system Ductwork Ductwork refers to the system of ducts (metal or synthetic tubes) used to transport air from heating, ventilation and air-conditioning (HVAC) equipment throughout your home. Properly installed and well-maintained air ducts are a key component of indoor air quality and home comfort. DUCT SHAPES Rectangular Shape Fit better to building construction. They fit above ceilings, in walls and between joints and studs. 1. Flat oval ducts have smaller height requirements. 2. 2. Oval ducts retain most of the advantages of the round ducts. Duct Shapes Round Shape 1. Lower pressure drops, thereby requiring less fan horsepower. 2. Less surface area and requires less insulation. 3. The acoustic of round ducts is superior, curved surfaces allow less breakout noise. 4. Healthier indoor environments, less dirt and grime accumulating inside the duct. Duct Materials Fiberglass 1. High Strength yet Lightweight. 2. Corrosion Resistant. 3. Non-Conductive 4. Fire Resistant. Stainless Steel 1. Durability. 2. Moisture Resistant. 3. Corrosion and abrasion Resistant. 4. High Cost. Galvanized Steel Fabric (Textile) 1. Lower cost (manual galvanization). 2. 2. Long Life (compared to other alloys). 3. 3. Toughness (High strength). 4. 4. Least Maintenance Cost. 1. Simplified Design. 2. Uniform Air Dispersion. 3. Cost Savings. 4. Lightweight. Duct Materials Chilled water system Chilled water systems are used in medium and large-sized buildings. Chiller plants act as a centralized cooling system that provides cooling for an entire building or even multiple buildings. This is because it is often more practical to centralize air conditioning equipment in one location rather than install many pieces of equipment in many different places. In addition to simplifying access for a building’s maintenance crew, large water chilled systems also provide greater energy efficiency than smaller, individual systems. Chilled water system The chiller basically removes heat from the water. It is used as a refrigerant to remove heat from the building. The chilled water circulates through a chilled water loop and through coils located in air handlers. Chilled water systems include other HVAC equipment designed to exchange heat such as computer room air conditioners. The chilled water absorbs the heat from the building. It then returns to the chiller where the chiller removes the heat from the water using the refrigeration process. Some chilled water loop arrangements are very complex while others are simple. Control of the chilled water from pressure to velocity, to volume, is up to the control system controlling the pumps and valve actuators in the system. Chillers range in size from smaller than 5 tons all the way up to several hundred tons. Chillers can be found in residential applications, commercial buildings, and industrial process applications. Chilled water system components Expansion tanks are required in a closed loop heating or chilled water HVAC system to absorb the expanding fluid and limit the pressure within a heating or cooling system. A properly sized tank will accommodate the expansion of the system fluid during the heating or cooling cycle without allowing the system to exceed critical pressure limits. The expansion tank uses compressed air to maintain system pressures by accepting and expelling the changing volume of water as it heats and cools. Chilled water system components Air Separators are used to separate entrained air in water through forced flow patterns. Air & dirt separators are designed to eliminate entrained air and separate debris associated with start-up and maintenance of any hydronic system. Symptoms of system air: 1. Inefficient operation 2. Noise in pipes 3. Corrosion Chilled water system components Valves are a device that regulates the flow of a fluid by opening, closing or partially obstructing a passageway. Valve types used in chilled water system: 1. Isolating valve ( stops the flow process to a given location) 2. Regulating and balancing valve (regulates pressure) 3. Non return valves (allows gas and liquid to flow) 4. Control valves ( two-way valve that works as an on/off switch) Chilled water system components BTU Meter accurately measures the thermal energy of chilled water consumption in British thermal units (BTU), a basic measure of thermal energy for commercial and residential buildings. BTU meter accurately measures the thermal energy of chilled water consumption in British thermal units (BTU), a basic measure of thermal energy for commercial and residential buildings. Chilled water system Advantages 1. Longer life span 2. Quiet operation 3. Energy efficient 4. No open space needed 5. Safety Disadvantages 1. Higher cost 2. More maintenance 3. Requires mechanical room 4. Less efficiency in humidity 5. Not ideal in drought sickened locations HVAC System Selection Consideration Types of Project 1.Residential • Low rise Buildings • Individual villas • Dwelling units • Hostels 3.Industrial • Data Centers • Pharmaceuticals • Food Processing • Textile ,printing 2. • • • • • Commercial Office Hotels Health Care Facilities Malls, stores Education Facilities HVAC System Selection Consideration Selected HVAC System for such application must cover all these requirements: Residential Buildings: Simple Controller Indoor Dimensions Aesthetic Hotels: Fresh Air Energy recovery Indoor Dimensions High-capacity zones Swimming area considerations Office: Fresh Air Power Sharing Heating and cooling at the same time Health Care Facilities Fresh Aim Energy Recovery Heating and cooling at the same time Operations theatre Precise Humidity controls HVAC System Selection Consideration The selection of most appropriate HVAC system is related to various parameters, including but not limited to: Life Cycle: Architecture: Capital (Initial) cost. Running (Operating) costs. Maintenance & spare part costs. Plant replacement costs (system lifetime). Available space for indoor & outdoor units. Mechanical shafts. Ceiling height. HVAC System Selection Consideration Thermal Comfort: The internal design conditions of an environment is a major focus in HVAC systems which depend on the activity level, age, and physiology of occupants.(ASHRAE standard 55). Efficiency/Performance and Energy Use: The selected HVAC system shall meet the needed efficiency and must conform with the constraints presented by ASHRAE 90.1. Each component of the system must use as little energy as possible while achieving the performance required. Environmental Constraints: The refrigerant technology is changing because of concerns of ozone depletion. Several commonly used refrigerants will soon end, including R-22 in 2010 and R-123 in 2020 in accordance with the requirements of the Montreal Protocol.
