Summary
Energy Considerations in Buildings
The objective of energy conservation is to use less energy and to recycle energy where useful. In the design of new facilities it is very important that the whole design team, including the client, have energy conservation as an objective. There is considerable synergy to be gained from a group effort. The client has the ability to set up a design contract that encourages energy conservation to the mutual financial benefit of the team and the client.
There are three ways of achieving energy conservation: Turn It Off, turning equipment off, Turn It Down, reducing equipment output and Turn It In, by replacing equipment with something more efficient. Of these three ways, ‘turning equipment off’ is usually the most cost effective, with ‘turning down’ second. Replacement is often not economic.
ASHRAE/IESNA Standard 90.1-2001
To assist in energy conservation ASHRAE/IESNA Standard 90.1-2001 Energy Standard for Buildings Except Low-Rise Residential Buildings was produced, and it is now being adopted in parts of the USA. This standard sets minimum
requirements for the building envelope, electrical systems including lighting, and the HVAC, under a prescriptive approach. The HVAC section covers the efficiency of individual equipment, as well as how they are to be interconnected and controlled. In addition, the design team may choose to meet the Standard using the performance route, the Energy Cost Budget Method, in which the design team demonstrate that their design will have no higher energy cost than the prescriptive design would have cost.
The requirements are designed to be easily cost effective and many programs, such as the LEED program, require substantially lower energy consumption than the Standard requires, to be recognized as energy conserving designs.
Heat Recovery
Heat recovery is the reuse of surplus heat from a building, often the exhaust air. Methods of recovering heat from the exhaust were described. These included:
Run-around coils, which are a system where a fluid, water or glycol mixture, is pumped through coils in the exhaust and outside air intake. This transfers heat from the intake air in summer and adds heat to the incoming air in winter. The system has advantages of no cross contamination and the intake and exhaust can be remote from each other just interconnected by the pair of run-around coil pipes.
The heat pipe and desiccant wheels were also described. They both require the intake and exhaust air to pass by each other and have a cross contamination challenge. On the other hand they are often less costly and more effective than the run-around coil.
Air-Side and Water-Side Economizers
The airside economizer is the use of outside air to provide cooling when the outside ambient temperature and humidity can provide ‘free cooling’. The system is not economic in very hot humid climates and it creates a low humid- ity indoors in cold weather.
The waterside economizer uses water, cooled in a cooling tower, to lower the incoming air temperature by means of a pre-cooling coil. The system takes up little space and does not require the large intake duct that the air–side economizer requires. It also has the advantage of not lowering the indoor humidity in cold weather.
Evaporative Cooling
Evaporative cooling can be direct or indirect. Direct evaporative cooling reduces the temperature and raises the humidity by direct evaporation of water in the air. For human comfort, this is a very acceptable situation in a hot dry climate but not useful in a hot and humid climate. For some industrial processes and greenhouses in particular, it can be very effective in all but the most humid climates.
Indirect evaporative cooling uses water that has been cooled by a cooling tower, or by direct evaporation on the outside of a coil, in the incoming air stream. Indirect evaporative cooling lowers both the temperature and the enthalpy. In many climates this can significantly reduce the required size of the mechanical cooling and drastically cut the electrical consumption by lowering the load on the mechanical cooling system.
Control of Building Pressure
If the building pressure is much higher than outside pressure, there will be leakage outwards. Similarly a low inside pressure draws air in through all the building cracks and leaks. Neither over nor under pressure is desirable, as they cause discomfort, energy waste and deterioration of the building fabric.
Bibliography
1. ASHRAE/IESNA Standard 90.1 2004 Energy Standard for Buildings Except Low-Rise Residential Buildings
2. ASHRAE User’s Manual ANSI/ASHRAE/IESNA Standard 90.1 2004
3. ASHRAE 2000 HVAC Systems and Equipment