Chilled water is a commodity often used to cool a building’s air conditioning equipment, especially in situations where many individual rooms must be controlled separately, such as a hospital, hotel or office building. The TEE approach to utilizing chilled water to cool a building environmental systems is to be a completely sustainable and energy efficient form of cooling that can rely on both renewable sources of electricity and renewable sources of heat energy to provide cooling through conversion processes.
Chilled water cooling is very different from typical residential or rooftop commercial air conditioning systems. In most residential and commercial roof top air conditioning equipment, the use ozone depletion chemicals known as refrigerants and high consumption of electricity to produce cooling on the basis of vapour compression refrigeration to provide air to air cooling. Chilled water cooling is different as it operates on and an air to water cooling cycle. Chilled water is pumped from a central plant chiller to the air handler unit to cool the air. Chilled water (between 4° and 10 °C) is circulated through a cooling coil in the air handler called an evaporator which cools and dehumidifies the return air from the conditioned space. This process in effect captures the heat from the air and cooler air is then dispersed throughout the area to be cooled. The returned chilled water will pick up the heat from the conditioned space to be rejected at the chiller for the cycle to continue.
The most common approaches for designing a chilled water system is to standard chiller is a two barrel system of both chilled water (space use) and condenser water (rejected to atmosphere). These water systems are isolate from each other. The water cooling the space is delivered at the temperatures discussed earlier and when returned through piping to the chiller returns at a warmer temperature. This heat must be rejected to the atmosphere via a series of transformations. The transfer of cooling and thus also heat from these water systems operates in balance with each other through a process of refrigeration through an isolated system of refrigerant liquid and vapour. The warmed water inside the chiller is referred to as condenser water which absorbs heat from the refrigerant in the condenser portion of the chiller. This water sent via piping to a cooling tower, which is a heat exchange device used to transfer waste heat to the atmosphere. The extent to which the cooling tower decreases the temperature depends upon the outside temperature, the relative
humidity and the atmospheric pressure. The water in the chilled water circuit will be lowered to the Wetbulb temperature or dry-bulb temperature before proceeding to the water chiller, where it is cooled to between 4° and 10°C and pumped to the air handler, where the cycle is repeated. The equipment required includes electrically operated chillers, cooling towers, pumps and electrical control equipment. The initial capital outlay for these is substantial and maintenance and operating costs fluctuate and are solely dependent on the supply of a reliable electrical system to operate.
TEE Chiller Principles
The TEE approach to a distributed chilled water system increases energy efficiency by eliminating some of the above standard electrically operated chilling equipment that consume massive amounts of electrical energy to operate. The TEE approach utilizes a passive transfer of heat using a series of water to water heat exchangers, efficient heat pumps, air to air chillers, water to water absorption chillers, water circulation pumps, piping, and a network of both internal building piping and geothermal piping in the ground. This replaces the “cooling tower” to reject the accumulated heat from within the building to the ground instead of the air. This principle works with more uniformity and isn’t subject to overcoming the ambient air’s ability to accept the heat being transferred. The ground source piping efficiently transfers this accumulated heat though heat transfer using direct convention. This efficient system reduces electrical consumption and also benefits the environment as the system doesn’t add extra heat to the air.
Thermal Storage Principles
Many conventional chilled water systems in North America are designed where this chilled water cooling process operates at night when electrical demands are less and thus utilities offer discounted off-peak rates. The chilled water is accumulated and then stored or “charged” in large, insulated tanks until needed, the next day for the cooling needs of the building or for operating during peak thermal demands for cooling. This reduces electrical cost as all that is required is the operating of circulating pumps to circulate the chilled water. Some systems use this process to create tanks of ice for circulating a smaller tank of chilled water. Ice storage requires less space than that of chilled water storage.
TEE Thermal Storage Principle
TEE envisions a process where this production of chilled water or ice production will be stored during the day utilizing the abundant energy provided by both the solar electricity, wind electricity generation and solar thermal energy. A self-sufficient system will effectively store and “charge” the cooled chilled water or ice with a portion of the daytime energy provided by the systems above. When effectively reversed this stored cooling energy in the form of the cooled chilled water or ice now operates the night time cooling process to operate solely on the electrical energy stored in batteries required to operate pumps and control systems.