The IWESS components are the individual systems that provide solar energy for space cooling and heating, power for lighting and equipment, chilled and heated water, cooling and heating for the IW and its occupants, and temperature and humidity adjusted ventilation air. These components exchange energy, electrical and thermal, with each other and with the campus power, steam, and chilled water grids. They comprise an integrated distributed power generation; a combined cooling, heating, and power, CHP; and a ventilation system.
An additional essential element of the IWESS project is the programming and exercise of mathematical models of the overall system – the IW and its occupants, the IWESS components, the campus grids, the Pittsburgh weather, and the operating system – to calculate over the course of a year its effectiveness, efficiency, and operating cost and to determine the effects of equipment design, system configuration, and operating rules on these significant quantities.
IWESS Component Rationale
Solar thermal system
Solar radiation is the fundamental, basic, energy source for the earth. Solar thermal receivers with parabolic trough reflectors, focusing on surface treated pipe absorbers in evacuated glass tubing, can recover 60% of the incident solar radiation as sensible heat at a temperature up to 200 oC in a fluid flowing through the absorber pipe. Currently available solar photovoltaic collectors recover 10 – 15 % of the incident solar radiation as electric power. Solar thermal heat can be used effectively in a two stage absorption chiller with a coefficient of performance of 1.2 to provide chilled water at 7°C for cooling a building in summer. This use is particularly effective since the need for building cooling is strongly correlated to the availability of solar radiation. Solar thermal heat can also be used in summer for regeneration of a desiccant for the dehumidification of ventilation air and in winter directly for building heating. The solar project component of IWESS explores the design, installation, and performance of solar thermal technology in supplying building cooling/heating/ventilation.
BioDiesel engine generator with heat recovery
The use of fuel produced from renewable sources provides an additional approach to addressing energy and environmental problems of the U. S. – the dependence on fossil fuel and the emissions of CO2. A bioDiesel fueled engine generator with exchangers for heat recovery from the engine exhaust and from the engine coolant can provide, using a renewable fuel at an overall efficiency approaching 80 %, electric power and thermal energy at temperatures up to 200°C for the operation of buildings – residential, commercial, and institutional. This bioDiesel component of IWESS explores the design, installation, and performance of such a systems and develops techniques for their control and operation.
Steam absorption chiller
Absorption chillers are key components in building cooling heating and power, BCHP, systems. They generate chilled water to be used in convective or radiant space cooling/heating units. Conventional vapor compression chiller units use electricity to provide chilled water. Absorption chillers are instead driven by thermal energy. The source of the thermal energy may be heat recovered from various sources, including power generation equipment and solar receiving devices. The combination of heat recovery equipment and heat driven absorption chillers provides significantly increased overall energy efficiency. Most of today’s building cooling and heating systems are not designed to make use of rejected heat.
Fan coils, mullions and radiant panels
Thermal energy embodied in chilled and heated water streams from the solar and bioDiesel components of the IWESS is piped to office, meeting, and work spaces in the IW for cooling and heating. This means of energy delivery is more effective and economic than circulating large streams of cooled or heated air. Cooling/heating units must then be provided in the IW spaces to deliver cooling/heating and thus to provide thermal comfort for the occupants. Mullion pipe, radiant panel, and ceiling mounted convective units are currently installed in the IW. Fan coil cooling/heating units are being installed to explore their effectiveness and to develop advanced control techniques for cooling/heating in the IW.
An outdoor air supply system has been installed to provide the required ventilation air to the occupants of the IW. This system incorporates a wheel based enthalpy exchanger between the incoming ventilation air and the exhaust air, an air based heat pump for cooling/heating the incoming air, a second wheel based dehumidification and heating unit regenerated by heat from natural gas. The performance of this ventilation unit is being measured and correlated to the details of its design and of its controls. The possibility of adapting this ventilation equipment to the use of recovered heat in chilled and heated water is also being explored.
An essential part of the work in IWESS is the programming and exercise of mathematical models of various IWESS configurations. These models integrate individual models of the IW and of its occupancy, of the various IWESS components, of the annual weather data, and of the operating rules for the overall system. These models calculate hour by hour throughout a year: the conditions in the IW, air temperature, humidity, etc; the quantity of energy in various forms consumed in operating IW; the cost of operation. They have proved essential in evaluating the performance of IWESS, in assessing the effects of modifications in system configuration and component design, andin formulating operating rules for the IW and the IWESS.