Services Flashcards
What do you know about Legionnaires Disease?
- Legionella is an aquatic organism
- Survives best at 40-65% relative humidity
- Cold water needs to be kept at a temperature of 20 degrees or less
- Hot water should be at 50 degrees within one minute
- No dead legs in systems
What is single phase electricity supply compared to a three phase supply?
Single phase supply has one single current, and one neutral
Three phase supply has three conductors all carrying alternating current of the same frequency and voltage. It can transport 3x more power with 1.5 cables. Good for heavy vehicles
What is the voltage provided at mains power sources in the UK?
240V
Why are there generally converters required between mains supply and power tools on construction sites?
Voltage: most tools operate at is 110V, as it is safer
What are Dry and Wet risers, and where would they be required?
Dry and Wet risers are provided within high buildings to allow a supply of water to be available in a fire fighting situation.
Buildings over 18m required to have either a dry or wet riser installed. Buildings over 50m require to have a wet riser. Wet risers are permanently charged with water, whereas dry risers are available but need pumping from a fire engine to provide water. They should be accessible within protected zones/fire fighting lobbies.
What are the two main types of sprinkler system?
Wet systems and air charged systems.
- Wet systems are permanently charged, so water is always available to the sprinkler head. They are only suitable in locations where there is no chance of freezing
- Air charged systems are filled with pressurised air, and when there is a drop in pressure, the valves release and water flows
What is the spacing required for sprinkler systems generally?
12m2 per head
4lm between heads
2m from wall to head
Who dictates the light levels required for different buildings and operations?
- The Society for Light and Lighting (Lighting Guide)
- CIBSE (lux levels for different properties)
Also, the building regulations impose lighting requirements in terms of sustainability
What is a Combination Boiler, and how does it compare to conventional domestic boiler?
A “combi-boiler” supplies water directly from the mains, heated by the boiler. It is more space efficient that a conventional boiler, and there is minimal delay in receiving hot water, and there is an endless supply of hot water. The disadvantage of combi boilers is that there is a flow rate reduction in high usage, it is dependent on the main supply pressure, and it tends to have a shorted life expectancy than conventional boilers.
What is a Conventional Domestic boiler, and how does it compare to a combination boiler?
A conventional domestic boiler takes water from a cold water storage tank and feeds it to a cylinder than is heated by a condensing boiler. Compared to a combi boiler, it has a faster flow rate, and has the option of multi-tap operation, the heating and hot water operate together, and they generally have longer life expectancy. However, the take up more space, there is time required for the water to heat, and they have higher installations costs.
What is R22 gas refrigerant?
R22 is an ozone depleting gas, which is used in some types of heating/cooling fan coil systems as the refrigerant. It’s use has been phased out due to it’s negative effects on the environment, from 2009 new R22 gas was banned, and as of 2015 R22 has been banned in general. It is still acceptable to use it in older systems, but if major repairs are required they may be banned. It can cause issues under a dilaps claim. In some situations it is possible to retrofit a different refrigerant, but it often effects warranties and the efficiency of the system.
What are chilled beams?
Chilled beams are rectangular units mounted in the ceiling void with chilled water pipework. Rising air is cooled on proximity to the chilled pipework, and forced to fall back down, therefore cooling the space. They are commonly used for large open plan office areas. They do not provide sufficient cooling capacity for buildings with high heat gains
Name 3 types of common commercial air conditioning system type
- Variable Refrigerant Flow (VRF)
- Four Pip fan Coil
- Variable Air Volume (VAV)
What is the difference between comfort cooling and air conditioning?
Comfort cooling is a system that provides ventilation or fresh air which can be heated or cooled. Air conditioning is also a system that provides ventilation or fresh air which can be heated or cooled, but it also controls humidity. Air conditioning systems will add water if low humidity or remove water in high humidity
What is a Variable Air Volume (VAV) air conditioning system?
VAV systems use air only as their heating and cooling mechanism. AHU supply air in zones providing heating and cooling. They take up a lot of space, and are quite inefficient. Not installed as new generally
