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Environmental protection and sustainable development calls for energy conservation in all operations of the hospitality industry. Poor productivity in the industry can be attributed to working conditions in the hot environment due to heat generated by mechanical equipment.
This has necessitated the need for a cooling system that is convenient. The invention of the cooling system was by Willis Havilland Carrier in 1902 and before that, man had used fans for cooling. The advent of this technology of cooling led to the invention of refrigerators and freezing equipment that operate on the same principle.
Any cooling system must incorporate airflow and cause changes in the temperature of the surrounding environment. Most cooling systems use a refrigerant gas that blows over a pipe that has cold water. In the actual sense, a cooling system has conditioned air and is not air conditioned as most people think. This is so because the air in the system is conditioned to ensure human comfort.
Reduction of energy use in the hospitality industry saves money, enhances corporate reputation and helps in the fight against climate change – one of the emerging global challenges.
Energy conservation became an issue of concern since the energy crisis in the 1970s. This issue greatly shaped the policies of every country. Most of the HVAC (Heating, Ventilation, Air conditioning) in the hospitality premises need to be operated for 24 hours a day and the systems must be as efficient as other systems. Such systems include an office operated at only the office hours.
In the hospitality industry, businesses should ensure that fresh air is circulated within the premises in order to ensure comfort of the clients. Apart from being an advantage in that it promotes customer satisfaction, it is also a legal requirement. This is according to the health and safety regulations.
Energy is required to heat or cool an indoor environment. Therefore, efficient ventilation systems are required to save energy. Furthermore, open windows and spaces within the building might contribute to loss of energy. Therefore, more air should be brought in order to ensure a cool environment while at the same time saving on energy. Buildings should employ methods that would help reduce air loss in order to reduce on costs.
In order for hotels to minimize costs, they adopt the use of water-cooled chillers to replace the original air-cooled ones. The optimization of air supply temperatures and the recovery of energy from the condenser tanks is an approach to energy efficiency in hotels. A decrease in pressure in the units implies an increase in the thermal efficiency. The cooling coils can then operate efficiently.
Centralized air conditioning systems
This is also referred to as the traditional air conditioning system. This system requires high energy and space. There is production of cold air in a central position and then the air is ducted to the various rooms in the building. The distribution to the individual rooms makes it possible for local temperature control to operate as the local system shuts down.
The advantages of this type of system are energy efficiency due to the conditioning by the air outside, heat recovery at the lowest possible cost and full conditioning at the lowest possible cost. There is allowance of alternative air conditioning options in this system.
This system has lower efficiencies that are associated with the fan motors making the system expensive and complicated. However, heat recovery is possible if the heat recovery uses the plate type heat exchangers (heaters or coolers). The regenerators in the system should have rotary mass storage heaters or coolers. There are high costs in this type of air conditioning as a result of the high airflow and the long distribution system requiring high energy for transportation.
Decentralized air conditioning systems
This is also called the partial air conditioning system and it offers a solution to both heating and cooling in buildings. The system allows for a high flexibility degree and individual control, differing from the centralized system. The advantage of this system includes the easy distribution of the cooling capacity. There is individual room temperature and the volume of air flowing can easily be adjustment. This system is less costly in structural costs as compared to the centralized system.
The challenge in this system is the air balance due to the wind pressure at the façade of the building. This leads to changes in pressure between the inside and the outside air. Subsequently, this causes fan operation-point changes. This calls for proper engineering to correct the problem in the decentralized system. Heat recovery is possible but only in restricted applications.
When the decentralized systems are fitted with pre-heaters, they require the least amount of time and energy. However, it should be noted that heat recovery is not a solution to energy conservation but it may result in higher demands. In this case, a suitable control system is required to solve it. Some of the decentralized units require package terminal air conditioning (PTAC). They are fitted in a sleeve on a wall and the device can be removed and replaced but the sleeve on the wall is permanent.
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They have a heating and cooling system. They can be a split system where the evaporator is located inside the building and the compressor is placed outdoors. Heat in the refrigerant is transferred to the outside by the condenser, which is normally placed outdoors in most of the commercial buildings such as hotels and offices. The placement of the condenser outside the building increases the energy efficiency of the air conditioning system.
The refrigeration cycle
According to the Boyle’s law, the volume of a gas is inversely proportional to the pressure upon it at constant temperature. This has lead to two principles on which the refrigerator operates. On heating, liquids change to gases and gases, on the other hand, give off heat when changed from gases to liquids.
Efficiency in the cooling system is attainable if a refrigerant is used. The air compression follows through certain processes that form a cycle commonly referred to as the vapor compression refrigeration cycle. The processes include compression, condensation, expansion and evaporation. These occur in a close circuit.
The refrigerant works in such a way as to displace heat from certain areas into other areas. When it comes into the compressor, it is usually in low pressure. However, it is compressed in the compressor and released at high pressure. From this point, the gas moves to the condenser. This is whereby the gas is condensed into liquid form. Since this process requires energy, heat is given off into the surrounding environment. This fluid then flows into the expansion valve.
This is done under high pressure. However, the valve blocks the liquid from flowing back. It also lowers the pressure as the liquid flows out. This fluid flows into the evaporator. Here, it is converted into gas as the heat is absorbed. The refrigerant then moves in form of a gas. At this stage, it is hot and at low pressure. Finally, the refrigerant moves back into the compressor. The cycle then repeats itself.
Water-cooled chillers are devices for removing heat from a liquid through vapor compression. The chilled water is distributed to heat exchangers or coils. There is then the redistribution of water back to the chiller to be cooled again. This process facilitates the transfer of heat from the air to the cold water.
As the surrounding air is cooled, it becomes dehumidified. These chillers may come in two forms. One of them is the closed loop system. This is whereby it is contained in a single unit. It may also be a spit system. This is whereby the components are located in different areas.
The chillers that are cooled using water incorporate the use of cooling towers. This helps improve the thermodynamic efficiency. However, this is not the case for the air-cooled chillers. Therefore, they are appropriate for indoor installation and operation. They have a separate condenser for the purpose of cooling. It is usually connected to the outside cooling towers in order to transfer heat to the atmosphere.
The cooling load that a given hotel requires may be affected by the occupancy level and this calls for a need for an automatic control system. The flow of chilled water in the chiller must be controlled. In the past, this new technology was not available. Therefore, this was done using valves.
Today, the chillers have frequency inverters that reduce the pump energy. They also ensure precise control of the rate of flow of water. The chillers usually have a large refrigerant capacity. Their efficiency also makes them appropriate for large applications. They are mainly used in commercial complexes in the hospitality industry since these buildings need huge air conditioning systems.
The control system: One of the systems used for ensuring efficiency in energy use is the programmable Logic Controller (PLC). It collects signals from the temperature, pressure and flow-rate sensors. Therefore, they control the operation of the chillers and pumps. In the hospitality setting, temperature sensors are situated outside the hotel building.
Pumps: Technology has made it possible for new pumps in most of the HVAC systems to be fitted with frequency inverters in order to cater for large variation in the cooling load. It also ensures that the flow rate of the chilled water is adjusted continuously. The frequency inverters ensure a constant pressure at the highest point with optimal efficiency.
Capacity and temperature: Energy efficiency is maximized in the chillers by having a small cooling capacity to ensure the chillers operate at full capacity. The temperature of the chilled water should not be too high. This would reduce the efficiency of the chillers. The temperatures of the water should be observed so as to determine its efficiency.
The control set point of the supply temperature of the cooling water should be properly set so as to avoid energy wastage through fan power. The water-cooled chillers have several advantages. One of them includes a long service life. They also have large output capacity and are highly efficient.
Air-cooled chillers function best in outdoor operations. These chillers are cooled directly by air. Air flows and circulates in the condenser coils providing a cooling effect. They do not require cooling towers as in the water-cooled chillers. Air-cooled chillers have some advantages such as requiring a small area for installation and less maintenance. They also do not require any condenser pumps or cooling towers and they have a low installation cost.
If the water-cooled chillers and air-cooled chillers are compared, air-cooled ones function without any condenser water pumps. Therefore, they require no initial installation and maintenance costs. Since they have a low condensing temperature, this compensates for the high costs of installation. Heat transfer is more efficient on wet surfaces than dry ones and this means that the air-cooled chillers require more power than water-cooled ones.
Precautions working with air conditioning systems
The systems require regular cleaning to increase their efficiency. Dirty equipment usually leads to inefficiencies, which leads to extra costs and greater risks. One must ensure that the filters are clean. This is necessary since dirty ones prevent airflow. To ensure a better flow of air, ensure the system is placed away from other objects.
Ensure other appliances in the building that may affect the functioning are placed away from the air conditioning system. For example, cloth dryers should be placed away from the air conditioning system to prevent increase in the heat demand and minimize the efficiency.
Insulation of the coil fins in the system with a masking tape is necessary to minimize the loss of heat to the surrounding environment. The coils fins must also be straightened to prevent blocking the flow of air in the air conditioning system. The coolant levels in the system must be checked to ensure that they do not fall below the required level. This is necessary to make the air conditioning system efficient. A dead band should be set. Heated and cooled air should never be passed through the system at the same time.
Another way of increasing efficiency is through recycling heat from exhausted air. This is necessary since it usually costs a lot to heat air within a building. Therefore, exhausted air should be re-circulated into the room while at the same time ensuring that the quality is not compromised. Variable Speed Drives (VSDs) are also important. They reduce the speed of the equipment in order to correspond to the needs at a particular time. Reduced speeds imply saved energy and reduced costs.
The complexities of most hospitality buildings require a flexible room layout and an effective thermal mass storage. The building materials used (such as glass) increase the solar gains and thermal load and this is further increased by the technology inside the building. Critical comfort requirements of air quality and room temperature are achievable if the latest air conditioning technology is put in place.
There is a need for cost reduction due to the escalating energy prices or government controls to limit primary energy consumption in a country. Energy saving potential from heating and cooling recuperation is a possibility in the hospitality business. Heat recovery is a possibility and this implies saved energy and lower energy costs.