Why Do You Have To Ventilate Your Subfloor?

Subfloor are easily prone to moisture problems. They have several cold spots, especially on the walls on the ground. In addition, they usually have very few windows or subfloor ventilation points. There is no possibility of optimal air circulation, hence the need for an efficient ventilation system.

Moisture problems lead to much more serious things if left untreated, even in a cellar. For example: the appearance of bad smells, a deteriorated quality of life, the birth of moulds and fungi (especially merules), which will impact on masonry and woodwork. The consequences of not treating cellar humidity are not limited to the cellars themselves. Over time, they are likely to spread to other rooms in the house, the upper floors, or even the entire building. You should therefore expect physical damage: wall coverings, ferrous objects (rust), etc.

But why invest in a Subfloor Ventilation? Isn't ventilation enough to ventilate a Subfloor? In fact, ventilation is equivalent to opening the windows in order to promote air circulation. Ventilation, on the other hand, is a mechanical and efficient process. They are indeed two very different things. In fact, ventilating the cellar is already very good, but it is not enough to clean the air and avoid the presence of humidity, mould... for a whole year. It is true that the air circulates, but not in an optimal way. Its flow rate is not controlled, especially since the polluted air cannot be discharged. The installation of new windows or doors leading to the outside is often difficult in the case of a cellar.

Ventilation Systems

Particular attention must be paid to the method of air distribution to eliminate excessive air flows and sensitive areas.

Regardless of the type of system, it should use mostly recirculated air with a minimum amount of fresh air for personnel. This helps to reduce the introduction of dust and latent heat and allows the system to cool the room under stable conditions. The different possible methods for managing air distribution and air conditioning in the computer room (CRAC) are illustrated in the following figures.

As a general rule, you should verify that the air inlet and outlet air temperatures of the air conditioning system meet the manufacturer's specifications.

Air Distribution Under False Floor

In the case of underfloor air distribution, the space between the floor of the building and the false floor is used as a means of conveying air for cooling equipment (see the following figure). Concrete floors may require special treatment to avoid dust emission. Air is released into the room via perforated tiles on the floor. The air is then returned directly to the air conditioning system or via a return collection means installed in the ceiling. You must remove all obsolete wiring (United States National Electrical Code standard) and plug all openings in the false floor that are not specifically used to supply air conditioning to the equipment air intakes.

The underfloor air distribution method tolerates a higher temperature of the air returned to the system without affecting the overall room conditions. This design takes into account a heat transfer factor via the metal false floor and also provides a certain amount of heated air to control the relative humidity before the air enters the room.

The temperature control system includes the same controls as the single duct system. In addition, the system must be able to control the air temperature at the underfloor air supply system so that the underfloor temperatures do not fall below the dew point of the room. The air entering the server via the connection ports must be within the allowable limits. (See Temperature and Humidity Criteria).

Combined Overhead and Underfloor System

For an air-conditioning system combining airflow above and below the floor, the primary air-conditioning unit is located in the room while the secondary unit is outside. Refer to the following figure.

An air management system, with separate controls, provides filtered and conditioned air at the false floor level. The air is then delivered to the room via floor vents. This air absorbs the heat generated by the server and is then released into the room from the top or rear of the server. The relative humidity of the air supplied to the computer equipment must be less than 80% and its temperature must be controlled to prevent condensation on or in the servers. It may be necessary to couple a heating system with the cooling unit to control the relative humidity.

The second air management system supplies air directly to the room via a separate supply system and must be capable of absorbing the remaining heat load in the computer room. It shall maintain the room temperature and relative humidity within the specified limits and provide continuous air conditioning and ventilation.

Air Circulation

In an air-conditioning system with air circulation, the entire heat load of the room or zone, including the heat generated by the computer equipment, is absorbed by the air supplied to the computer room and zone or by a pressurized ceiling-mounted system.

The air returned to the air conditioning system comes from ceiling vents above the heat-generating servers or from both ceiling and wall vents. The following figure shows an air conditioning system with air circulation.

To optimize the cooling capacity of this system, it is imperative to place the supply nozzles in the cold air corridors and to place the intake grilles in the warm air corridors. The supply nozzles must force the air supply directly into the bottom of the cold air corridors without using a side distribution air diffuser. This type of air distribution can have the effect of directing the cold air to the return air path before it has absorbed the heat emitted by the machines.

Any temperature control system should include temperature and humidity measurement instruments. These control instruments should be placed in the computer room in a location representative of the overall environment. The temperature and humidity recorder (see description in Temperature and Humidity Criteria)) should be placed next to the weather monitoring controls.

Air Filtering

An efficient filtering system must be installed to filter all air supplied to the computer room. Since electrostatic and mechanical air purifiers operate on different principles, there is a specific evaluation method for each type. Ratings are determined using the test methods described in the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) Standard No. 52-76 (or your national equivalent). Special air filtration is required when installations are exposed to corrosive gases, sea air, or unusual dirt or dust conditions.

Mechanical air filters should be rated at a minimum initial atmospheric dust level of 40%.

Electrostatic air filters are designed to provide 85-90% efficiency at a given face velocity. The filter shall be used in accordance with the manufacturer's recommendations to prevent the accumulation or leakage of ozone which may be detrimental to certain servers.

Single Flow Ventilation

This technique helps you to renew the air inside the subfloor. It works in particular with the help of an electric extractor. This extractor is placed on a higher level in order to suck out the stale air from the inside. Then, fresh air is blown in (also known as fresh air).

Double-flow Ventilation

Here, an exchanger is required (hence the name "double flow"). In this way, the heat of the extracted air is recovered. The same heat is then sent to the supply air. There is no risk of a mixture between these two air streams: extract and supply air. On the other hand, it's all about the heat.

Whatever the solution that suits your subfloor, avoid doing it the home made way. The best thing to do is to call in professionals! You will then benefit from an initial diagnosis, and then an estimate. The treatment your subfloor will receive will also be appropriate.