Space heating systems are designed to satisfy the thermal comfort requirements of building occupants. The interaction of the heating system with the fabric of the building is critical to the comfort achieved and the energy efficient operation of the system.
It is therefore necessary to appreciate the thermal comfort requirements of people (see Air Conditioning) and the thermal performance of the building fabric (see Building and Heat Transfer) before understanding space heating systems and their operation.
The design of the heating system is based on the steady state heat loss of the building, or the heat output required to maintain comfort conditions within the building with an accepted external design temperature. The procedures for calculating space heating loads are described in Chapter 25 ASHRAE Handbook of Fundamentals (1993), the CIBSE Guide Section A3 (1980), and Section A5 (1979) as well as in Mc Quiston and Parker (1994).
Estimation of the energy requirements and the predicted fuel consumption for space heating, however, must be based on a dynamic appraisal of the building throughout the heating season. It must take into account the hours of occupation of the building and the changes in external conditions throughout that time. The efficiency of the heating system and the thermal performance of the building fabric.
Buildings can be divided broadly into heavyweight and lightweight structures. A heavyweight building is slow to respond taking a long time to heat up, but similarly a long time to cool down. It is therefore particularly well suited to buildings that are occupied on a continuous basis and for heating systems that are slow to respond.
Lightweight buildings on the other hand respond quickly both to the external environment and to the space heating system, which must be flexible and controllable to take advantage of such a response. The intermittent use of many new buildings is often suited to a lightweight structure and a responsive space heating system.
Different space heating systems have characteristics that include speed of response, flexibility of control, space required for installation, initial cost of plant and installation, maintenance and energy costs, the fuels they use and their impact on the environment.
Space heating systems can be divided into direct and indirect acting heating. Direct systems convert fuel to heat within the space to be heated, for example, open coal fires, gas radiant or convective heaters and the majority of electric heating systems. Indirect systems, on the other hand, convert the fuel energy into heat in a central position from where it is distributed around the building and emitted to the space. An example is a radiator system served by a hot water boiler or a warm air heating burner.
Detailed descriptions and design consideration of the various system components are given in the ASHRAE Handbook of HVAC Systems and Equipment (1992). These include:
|Automatic fuel-burning equipment||Chapter 27|
|Residential in space heating equipment||Chapter 30|
|Chimney, gas vent and fire-place systems||Chapter 31|
|Making up air units||Chapter 32|
ASHRAE Handbook of HVAC Applications (1991) describes in detail the various design considerations associated with different applications.
Heat can be distributed from a central boilerhouse to the individual heated spaces by water, steam or air. For small scale buildings, water distribution is at atmospheric pressure, but by pressurizing the system a greater temperature drop across the circuit can be achieved and therefore greater heat output obtained from the same volume of water. High pressure water, like steam must be utilized by heat emitters out of reach of the building occupants or by means of heat exchangers and secondary circuits.
Detailed method of calculation is given in Chapter 6 of the ASHRAE Handbook of HVAC Systems and Equipment (1992).
American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., ASHRAE Handbook 1993, Fundamentals Volume, Atlanta, GA.
American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., ASHRAE Handbook 1991, HVAC Applications, Volume, Atlanta, GA.
American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., ASHRAE Handbook 1992, HVAC Systems and Equipment Volume, Atlanta, GA.
Chartered Institution of Building Services Engineers, (CIBSE) 1979. CIBSE Guide Book A
Chartered Institution of Building Services Engineers, (CIBSE) 1980. CIBSE Guide Book A, Section A3 Thermal Properties of Building Structures.
Mc Quiston, F. C. and Parker, J. D. (1994) Heating, Ventilating and Air Conditioning, Fourth edn., John Wiley and Sons, Inc., New York.