Mechanical Systems
Ventilation
Ventilation is the process by which ‘clean’ air is intentionally provided to a space and stale air is removed. This may be accomplished by either natural or mechanical means. On projects it may also be referred to as Ductwork or HVAC (heating, cooling, air conditioning).
Natural Ventilation
This is normally found in your own home depending on location and climate.
Mechanical Ventilation
This is more common in public buildings and offices.
Why is Ventilation needed?
- To ensure good air quality
- To prevent condensation
- To dilute odours and carbon dioxide
- To control temperature
How it works
Fresh air from outside is sucked into the air handling unit (AHU). The air handling unit cleans the air, then either heats up or cools it depending on what the building requires and sends this air throughout the building via the supply duct. When the air goes into the room via a supply grille, it heats up, rises and leaves the room through the ceiling return grilles.
This return air makes its way back to the AHU via the return duct. A portion of the return air is filtered, reconditioned and sent back to the room. The rest is left out of the building through the extract duct.
AHU Design
Other equipment associated with the Ventilation System
FCU (Fan Coil Unit)
As multiple rooms are supplied by the same AHU. You will need additional equipment such as a FCU to allow you to able to control the temperature in different rooms. For instance if you wanted one room to be at 18 degrees and the other at 20. You wouldn’t be able to do this with the one AHU. A FCU will typically have a heating and cooling supply. For the majority of rooms in countries like Ireland/ the UK, you will only need the air to be heated as we do not experience the high temperatures as in other parts of the world. For rooms with a high occupancy rate such as meeting rooms, you would need additional cooling.
Heating Coil
A heating coil has a similar function as the FCU as it allows you to have different temperatures in rooms fed from the same AHU. However there isn’t any cooling feature. How it operates is that if all of the rooms supplied by the AHU require temperatures between 16 and 20 degrees. The AHU will produce air at 16 degrees and the rooms that need anything above that will be boosted by the heating coil.
Cooling (Chillers, DX units, VRF System)
The majority of buildings will need some form of cooling. Be it offices, other work spaces, hospitals and especially Data Centres. Unlike the cooling required for an office to ensure the occupants are in a comfortable environment, a Data Centre needs cooling to ensure the sensitive equipment doesn’t overheat and shutdown.
Types of cooling -
- Chillers
- DX System
- VRF System
Chillers
Chillers are large Mechanical equipment which uses refrigeration to cool water flowing around in metal pipes. When air passes over this cool pipe it removes heat from the air and thus cools it.
Like your refrigerator at home there is a chemical inside it that when its put under pressure it will condense into a gas and extract the heat from its surroundings. In this case the water in the pipe. If you take the heat out you are left with cool water. The cool water is sent around the building to cool the air. As this cool water is cooling air it is actually heating up. When it comes back to the chiller it may have heated up by a few degrees. It then passes through the chiller again and is re-cooled. The cooling tower at the top of the chiller will also be used to dump some excess heat.
DX Units
Direct expansion is the most commonly used type of air conditioning. Dx units include room air conditioners, split systems, ducted systems and package type units. A Dx air conditioning system is often just a technical term for a standard home air conditioner or commercial HVAC system.
DX Outdoor Unit
A DX system cools the air by transferring condensed refrigerant to the heat exchanger located inside the building. It has a component called an evaporator where the refrigerant expands as heat is being generated and absorbed, before ultimately turning it into gas.
DX Indoor Unit
The simplest explanation of VRF is to describe it as a large-scale ductless HVAC system that can perform at a high capacity . The specific design of a VRF system varies based on application. In general, VRF technology provides the ability for multiple indoor units or zones to operate on the same system.
VRF System (Variable Refrigerant Flow)
The simplest explanation of VRF is to describe it as a large-scale ductless HVAC system that can perform at a high capacity . The specific design of a VRF system varies based on application. In general, VRF technology provides the ability for multiple indoor units or zones to operate on the same system.
Heating
For most commercial projects the DX/VRF or Heat recovery systems provides sufficient heating for occupied spaces. For other large scale projects a primary heating source may be required.
This is often provided by the installation of a boiler. A boiler is a large piece of mechanical equipment that can use Electrical, Gas or Oil to heat up a liquid that is then circulated around a building to heat up the rooms.
The hot water from the boiler is pumped around the building to the FCU’s and Heating Coils. When the fresh air passes over the hot pipe it heats up the air and thus the room.
The hot water from the boiler is pumped around the building to the FCU’s and Heating Coils. When the fresh air passes over the hot pipe it heats up the air and thus the room.
CHP units can be used to fully replace inefficient backup gensets if the data center load profiles (electric, heating, and cooling) allow for it.
In the heating system and most other systems there will be a flow and return. This is to make the most efficient use of the energy used to produce heat. When the boiler heats up Supply Return Gas Line
Supply in and return out the water to the required temperature it is sent around the building.
When it heats up the spaces it loses its heat by a few degrees. This lower temperature water then goes back to the boiler in the return pipework and passes back through the boiler where it is reheated up to the required temperature.
This is cheaper than using fresh water and heating it up from a much lower temperature.
DWS System - Domestic Water System
The domestic water services is all mechanical works (piping) associated with fresh potable (drinkable) water supply to a building. For your sinks, showers, baths you will need a cold and hot water supply. For your toilets and drinking fountains you will need a cold water supply.
The hot water will be generated from your boiler. You will see in the diagram below that the tank on the right is the Potable water. There is a pipe coming from the boiler that goes into and out of the this tank. The water doesn’t mix but the heat from the pipe will heat the potable water.
Plant and pipework systems can be manufactured off site and delivered on skids
For the DWS system there will be large storage tanks fed off the mains water supply (MWS). The water from this is pump when required to the DWS skids, filtered and then heated if required.
Foul Waste Drainage
The Foul Waste System will collect waste form WCs, Showers & Kitchens, and connect into the local area network.
There will be a connection off the sanitaryware to a main stack which allows the wastes to be removed.
There will also be a vent pipe which will trap the odours and release them outside the building.
Storm Water Drainage
Data Centers, provide unique circumstances and challenges for rain & stormwater attenuation & detention
The surface area of multiple campus buildings and road networks can create large catchment areas for rain & storm water.
Rain water from building surface can be stored in temporary attenuation tanks for discharge into the network at a later time.
Storm water from other surface areas can be stored in interceptor tanks, or open ponds
BMS (Building Management System)
A Building Management System is a computer-based system installed in buildings to manage and monitor equipment such as air-conditioning, heating, ventilation, lighting, power systems, among others.
The thermostat on the wall that controls the heating system is a part of the BMS system. When you want the room to heat up you will change the temperature on the thermostat.
This sends a signal to the boiler to turn on and this heats up the water to the required temperature.
Another example of the BMS system is when a fire is detected. When its detected it will send a signal to the ventilation system to stop pumping air around the building. It will also close the MFSD (motorised fire smoke dampers) to prevent air/smoke/flames from travelling through the ventilation systems.
