Cold Water System
For the cold water system in this property, the tank must be well insulated and well supported together with a dustproof cover in order to avoid contamination. This is vitally important in a dwelling as there will be limited cold water usage in a house this size, the normal of 90 litres/person/day will apply but it is likely that there will be only 3/4 people living in this house. For the storage, only a small tank would be required as the mains water pressure would be enough to pump the water to any point of the house. The cold water storage tank would link to the hot water cylinder as the way of getting water into that tank. The system must conform to the Water Supply (Water Fittings) Regulations 1999 as seen below.
Air Conditioning
It is common for houses to have packaged systems. However, these are less effective than specific air conditioning systems. The packaged system is normally used for houses that are unable to accommodate built in air conditioning systems. There are two types of packaged system. Firstly there is the self-contained package which is suitable for small rooms (like those in a house) and is free standing. There is also a split package which can span over a number of rooms as there are two units in this package. For more modern and high-spec houses, a built in system can be incorporated. A more common system would be the perimeter induction unit system. This is where the system is located normally under windows and they blend primary air from the APU with the secondary air from within the room. The air is induced into the unit through certain restrictive nozzles. This air intake thus produces negative pressure therefore drawing secondary air into the unit. The air will then mix and then release which is controlled by a damper which is thermostatically controlled.
Multi-Storey Commercial Office Building
Hot Water System
Where as small buildings only have one circuit, larger buildings require a secondary circuit to reduce ‘dead-legs’ and to keep an effective supply of hot water at all outlets. In buildings such as this which will only be occupied for part of the day, a time control/programmer can be used to regulate the use of the pump. The valves near the pump should be motorised and automatically shut off with the pump when hot water is not required. The secondary circuits should be well insulated to ensure that there is minimal heat loss from the pipe work. To reduce wear and tear on the fittings, the maximum head of water above taps and other outlets is 30m. This is possible by using break pressure cisterns for each of the sub-circuits. Head tanks are provided to ensure that a sufficient volume of stored hot water is readily available to be delivered to the upper floors. With this system, a lot of pipe work and fitting time can be saved compared to conventional installations. The boiler and calorifiers must of a high specification to withstand the pressure of the water. Also, all the pipe work must be well insulated.
Cold Water System
For buildings of this size, the pressure from the mains system is not high enough to supply water directly to the upper floors. Boosting by pump from a break tank is usually necessary & several of these tanks may be required depending on the height on the structure. On the down services, there should be just as many break tanks due to the head of pressure on the lower floor fittings. The maximum height, like that of a hot water supply, should not exceed 30m. The drinking water header pipe or storage vessel will supply the drinking water to the upper floors. When the tank empties to a pre-determined level, a float switch will be activated and will engage the duty pump. The reason for having the float switch is to stop the tank from being fully emptied of water (known as ‘dry running’). All pipe sections in the building should be fitted with isolating valves in order to make general maintenance & repairs more easily done.
Alternatively to the drinking water header pipe, an auto-pneumatic cylinder may be used. Compressed is in the cylinder will force air up through the float valves & to the drinking water on the upper floors. As the cylinder empties, a low pressure switch engages the duty pump. When the pump has filled up the cylinder, a high pressure, switch disengages the pump. As this happens, the float switch detects the high water level in the cylinder & activates an air compressor in order to maintain the air pressure.
Air Conditioning System
The most common system of air conditioning in an office block would be the Variable Air Volume system. This system has a central APU to produce the air at a specified temperature and relative humidity. The air that has bee processed travels from the main unit through ductwork to the ceiling diffusers which incorporate thermostatically controlled actuators. These change the air volume to suit each separate room. In larger rooms (e.g. open plan offices) several ceiling unites may be controlled by a single thermostat. Many rooms will have separate thermostats to control the air flow. The inlet fan can have variable pitched impellers operated by the compressed air. The angle of the pitch is controlled by a pressure switch. The air temperature for each room can be varied. However, in office buildings, it is likely that everybody will want around the same temperature which is what this system provides best. The air usually comes out of the ceiling units at a rather fast speed.
Bibliography
All Pictures are from Building Services Handbook – Greeno
Books used in the writing
Building Services Handbook – Greeno
Building Construction Handbook – Chudley
Classroom notes.
