Entropic provide unique solutions for the various ventilation needs of the modern healthcare sector.
Ventilation is used extensively in all types of healthcare premises to provide a safe and comfortable environment for patients and working staff. More specialized ventilation is provided in areas with more specific requirements, such as patient treatment areas which include operating departments, critical care areas and isolation units.
It is also installed to ensure observance with quality certainty of processed items in pharmacy and sterile services departments, and to protect staff from harmful organisms and toxic substances (for example in laboratories).
The sophistication of ventilation in healthcare premises is increasing. Patients and staff have a right to expect that it will be designed, installed, operated and maintained to standards that will enable it to fulfill its desired functions reliably and safely.
Zoning of the building
The efficiency and effectiveness of any ventilation or air-conditioning installation depends largely on the zoning and control of the installation. The factors to consider when determining the zoning of a ventilation system for a building or department are:
- Periods of occupancy
- Fresh-air/ventilation requirements
- Smoke control
Where the ventilation system is not only tempering the air, but also providing the heating and/or cooling requirements, the following additional factors will need to be considered:
- Internal or peripheral location
- Orientation of windows
- Variation in internal loads
- Level of control required
Entropic’s patient room solutions are designed using chilled beams. This is an extremely energy efficient system that reaches the desired air temperature and velocity and has a low operating sound level. Chilled beams are suitable for healthcare projects as they are easy to maintain and clean, keeping the environment as hygienic as possible. An example of a chilled beam system is St. Anne’s Day Care Ward in St. Vincent’s Hospital. Our solution was to replace the existing radiant panels with active chilled beams to provide heating, cooling and ventilation.
Selection of design criteria
Minimum fresh-air requirements
The dilution of body odours is the critical factor while determining ventilation requirements. Where natural ventilation or full fresh-air systems are used, all ventilation air will be fresh.
Where odour dilution is the overriding factor, it is recommended that 10 liters/ second/ person should be taken as the minimum ventilation rate.
In non-standard applications such as laboratories, aseptic suites, operating departments etc, the particular requirements for each area should be considered independently in order to determine the overriding minimum requirement for ventilation.
Limiting supply air conditions
For most applications in healthcare buildings the critical factor is the temperature differential between the supply and room air rather than the actual temperature of the supply air. The maximum recommended supply-to-room-air temperature differential is:
- Summer cooling: –7 K
- Winter heating: +10 K.
In areas that have high heat gains from equipment (for example critical care areas), the summer cooling temperature differential limit given above may result in excessive air-change rates.
A differential of up to –10 K is acceptable in these circumstances, providing the supply-air diffusers are of a type that provide good mixing.
If a humidifier is fitted, it is necessary to keep supply-air humidity below 70% during winter in order to minimize the risk of condensation on cold surfaces.
In healthcare premises, the standard of filtration will depend on the activities within the occupied spaces. With the exception of specialist areas (for example manufacturing pharmacies), aerobiological requirements are not stringent, and filtration is only required to:
- maintain hygienic conditions for the health and welfare of occupants, or for processes such as food preparation
- protect finishes, fabrics and furnishings in order to reduce redecoration costs
- protect equipment either within the supply air system (that is, to prevent blocking of coils), or in the space itself to prevent dust build-up
Given that almost all viable particles originate from the occupants of a space and not from the incoming air, dilution is the more important factor aerobiologically. Therefore, for general areas a G4 filter is suitable. More critical areas will require an F7 filter. High-efficiency particulate air (HEPA) filters are required only in ultra-clean systems.
Noise is typically generated by fans, ductwork fittings, dampers and grilles. The specified maximum noise level will depend on the activities within the occupied spaces.
The reduction of tonal components needs to be given attention. High tonal components from air diffusers can weaken concentration over longer periods even when the overall noise level is low.
Attenuation should be incorporated into the ductwork system or plant arrangement as necessary to reduce noise from fans and plant items in order to achieve acceptable limits within rooms at the design air flows.
The designer must also consider noise escaping to the external environment, and this must not be unacceptable to occupants of adjacent areas or buildings.
The overall noise levels should not exceed the values given in Health Technical Memorandum
Plant noise is subject to the Control of Noise at Work Regulations 2005 and should not exceed 80 dB(A) within a plant room. It should be reduced to lower levels where the plant is near to departments sensitive to noise.
Air distribution system
Diffuser and grille selection
The effectiveness of all ventilation and airconditioning systems relies on the methods than bring air to the space and how vitiated air is removed. The usual results of poor air-terminal selection and/or positioning are:
- Poor air quality
- Large temperature gradients
- Excessive noise
Air supplying devices can be grouped into two different categories:
- Produce a diffused supply
- Produce a perpendicular jet
Diffusers may be radial or linear, and normally utilize the Coanda effect (adhesion of the air stream to an adjacent surface) to reduce the risk of excessive room-air movement. A perpendicular jet is formed by fullfilling air through grilles, louvres or nozzles, which are generally adjustable.
Supply air terminals can be incorporated into any room surface (for example floors, walls (high or low level) and desktop).
As they operate on the jet principle, the use of sidewall and linear grilles is restricted to areas where air-change rates are fewer than ten per hour. Perforated rectangular diffusers can provide acceptable conditions within the occupied zone at up to 15 air changes per hour. In areas where a higher air-change rate is required, square or circular ceiling-mounted diffusers should be used.
The performance of supply air-terminal devices is based on three criteria:
- throw – defined as perpendicular or parallel distance from the terminal to the point at which the air velocity is 0.5 m/s isovel
- spread – defined as the width of the 0.5 m/s isovel
- drop – defined as the vertical distance from the centre line of the terminal to the bottom edge of the 0.25 m/s isovel.
Transfer grille – size and location
Air-transfer grilles in walls, partitions or doors form an integral part of the building’s air distribution system. Modern door sets have very low leakage rates, so cannot be relied upon to permit even quite small air flows. Failure to make adequate provision for air to move from room to room will result in pressure differentials and “door whistle”.
Transfer grilles are required in locations where there is a considerable imbalance between the supply and extract rates in a room. They will relieve any pressure differential that may affect the operation of the spaces and/or the ventilation system, and permit air flow in a known direction.
Pressure stabilizers – size and location
Pressure stabilizers are required in areas where it is necessary to maintain pressure differentials between adjacent rooms to prevent reversal of air flows (for example in operating suites, isolation facilities and clean rooms.
Fire precautions for pressure stabilizers are the same as for transfer grilles.
Pressure stabilizers should be of the balanced-blade type, with the facility to make fine adjustments to the pressure setting. They should be silent in operation and give a seal as tight as practicable when closed. The materials of construction and method of assembly should allow for cleaning and disinfection.
Pressure stabilisers should be installed in a visible location so that their operation can be readily observed.
Pressure stabilizers may need to be fitted with a stand-off baffle on their discharge side to prevent a sight line in situations where a laser will be used. Baffles may also be required to preserve privacy or to prevent discharge air causing droughts or disturbing the air-distribution pattern in an adjoining room. They are also useful in low-level locations to prevent the air-flow path being obstructed by portable equipment.
It is necessary to consider each of these parameters in both summer and winter conditions to ensure satisfactory operation of the air-terminal device, as warm jets behave very differently from cold jets.
A warm jet tends to rise until it attaches itself to a horizontal surface, while a cold jet falls. It must be taken care of so it does not lead to unacceptable temperature gradients in winter, or excessive air velocities in the occupied zone in summer.
In order to ensure satisfactory air movement within a space, it is necessary to consider interaction between air movement from adjacent terminals and ceiling-mounted fixtures (light fittings etc), as well as interaction between air movement and room surfaces.