Fans in Healthcare
Maintaining a Healthy Environment in Health Care
Behind the scenes of one of the essential services in the UK, fans are used to provide the delivery of air for several reasons.
Fresh Air Supply
There is no substitute for fresh air to provide a healthy environment in a healthcare building. On the wards, in the corridors, in treatment rooms, where staff, patients and the visiting public have access, fans in air handling units ensure a constant supply of fresh air and extraction of stale air. The supply of fresh air elevates the oxygen concentration whilst the removal of stale air reduces CO2 / NO2 levels, extracts odours and other contaminants created during daily operation. To condition the air before it enters the hospital, air handling units (AHUs) clean, condition and manipulate the temperature of the air according to comfort and the design criteria for the building. The AHUs use fans to force air through particulate filters, heat recovery cells, heat exchangers and building ductwork; overcoming the resistance of these components to deliver volume of air required.
Over time, elements of the AHU will require maintenance. As air from the outside world passes through the intake, contaminants such as dust and debris are drawn in to the AHU. As a result, components such as particulate filters become clogged and their resistance to flow increases. An increase in resistance carries the consequence of a reduction in flow rate which will affect the indoor air quality inside. To overcome a drop in fresh air supply due to dirty filters, a fan with a self-balancing control system can be chosen. Measuring and adjusting the volume flow passing through the fan can provide a constant volume of air through the air handing unit as the filters become progressively clogged.
Constant volume control can be achieved using backward curved fans fitted with pressure tappings on the fan inlet ring. Taking a reading of the pressure before the fan and at the inlet ring shows a static pressure drop. This pressure drop is in proportion to the amount of air passing through the inlet ring and can be used as a target set point for a control system to modulate the fan speed against.
Constant volume control can be used on a single backward curved fan or an array of backward curved fans as used in larger air handling units.
Typically, AHU’s make use of large frame mounted backward curved centrifugal fans supplied complete with inlet ring pressure tappings for volume flow measurement. Of all the fan types, a backward curved motorised impeller is the most efficient fan in terms of converting electrical input power to air power output. When the volume flow required is high, several fans can be mounted in an array to provide the required flow rate as well as redundancy should there be an operational issue with one of the fans.
Contamination Control – Hospital Operating Theatre
A sterile environment is an ideal condition when an operation is being performed. Equipment and implements are maintained and cleaned before each operation, minimising the risk of contamination. Personnel involved in the operation follow a process which limits the risk of bringing vaporous or particulate contaminants into the operating theatre. However meticulous the preparation, there is still a residual risk of particulates being introduced and carried on air currents around the operating theatre.
Picture Courtesy of http://www.samirhanigroup.com/v2.0/?page_id=1980
To limit the risk of a contaminant being introduced, a laminar flow hood placed in the ceiling above the operating area can be used to ensure that there is a flow of constant velocity from the ceiling to the floor.
A laminar flow hood has 2 features of interest:
- Anyone entering the operating area within the operating theatre will first encounter a wall of air blowing any particulates on their person down to the floor and away from the operating table and the patient
- A constant velocity of, clean finely filtered air over the patient and personnel means that exacting control can be exercised over the conditions under which the operation is taking place. Like an AHU, this system uses particulate filtration. The difference with this system is the high level of filtration which is usually achieved in stages, (Coarse filter followed by medium grade filter followed by fine grade filter).
Control for this type of application can be achieved by constant volume or constant velocity:
Constant volume control maintains the velocity in the operating area using the relationship between flow, velocity and cross-sectional area
Volume Flow (m3/s) = Velocity (m/s) x Area (m2)
If the cross-sectional area of the laminar flow hood and the velocity required is known the volume flow required can be calculated. This value can then be used as the set point for a constant volume system to maintain a volume flow rate whilst the particulate filters become blocked with time.
Constant velocity can also be achieved using a hot wire anemometer placed a short distance under the laminar flow hood. A hot wire anemometer uses two temperature sensors; one in the path of the air and one sheltered from the air path. Air flowing over the anemometer creates a cooling effect on the thermistor placed in the path of the air leading to a temperature differential. The temperature difference between the two thermistors is in proportion to the velocity of air passing over the anemometer. If the temperature differential at the desired flow rate is known, this can be used as a set point that provides the basis of fan speed modulation.
An alarm can be added into the system should the fan not be able to maintain the desired set point if the speed of the fan has reached a threshold level. The alarm can be used as a trigger point to maintain the system and change the dirty filters for clean.
Environmental Control – Pharmaceuticals
Medication, particularly those that take the form of tablets or powder, can create dust during handling and packaging. Other chemicals used to treat medical conditions in liquid form, can evaporate at room temperature.
To protect operators and personnel involved in the handling of medication and the effects of inhalation of dust or vapours, a variety of methods can be used.
Laminar Flow Booth
The operation of handling and processing medication in tablet or power form can take place in a down-flow laminar flow booth, which is similar in design to the operating theatre. Air is drawn into the air filtration system at low level, through particulate filters into the fan and into the ceiling of the booth which creates a constant, laminar flow with uniform velocity across the booth. This ensures that any pharmaceutical dust created is blown down and away from the operator within the booth.
Downflow systems can be installed in limited space or can be designed to encompass a whole room. Most typically controlled by ensuring a constant volume flow, control can also be achieved using a hotwire anemometer.
Like the AHU, Laminar Flow Booths use frame mounted backward curved motorised impellers for their efficiency and the capability to accurately control the air velocity output.
Laminar Flow Cabinet
Used where there is a risk of vapour as well as dust, a ‘Reach-in’ laminar flow cabinet. This equipment uses an adjustable window at the front of the cabinet through which the operator can reach in to handle and mix medications and chemicals. The fan circulates air in a controlled air path through the cabinet creating an air curtain that keeps the dust and vapours inside avoiding contact with the operator outside. This type of product uses fine particulate filtration in conjunction with an active carbon filter to neutralise any vapours that are circulating within the controlled area.
Dependant on the size of the cabinet and its space constraints, fans used in this type of application include backward curved motorised impellers as well as single and double inlet forward curved blowers. Control of the fan is based on the velocity of the air curtain where the operator reaches in.
Types of fans used in this application include backward curved motorised impellers as well as single and double inlet forward curved blowers…
RS Stock no (218-3208)
RS Stock no (876-5162)
RS Stock no (830-3023)
RS Stock no (841-4911)
Local Exhaust Ventilation
In smaller environments where space is at a premium and the requirement to handle pharmaceuticals is less common, a simpler option with minimum investment would be to use a local exhaust unit. Operating in a similar manner to that of a vacuum cleaner, an extract ventilation nozzle is placed close to the point at which the work is taking place. Air is drawn in through the nozzle by a fan in the base unit which passes the air through a particulate and active carbon filter before recirculating it back into the room.
Typical fans used for this type of application are single inlet centrifugal fans mounted in a scroll housing. Usually used in the boiler industry their slim impellers rotating at high rotational speeds produce a high suction pressure to overcome the resistance of the filtration. This type of blower is powered by an electronically commutated motor that can be controlled to increase the speed / performance as the filters become progressively clogged.
RS Stock no (514-2979)
Where hazardous contamination is present and personnel are required to enter the hazardous zone, a high level of respiratory protection may be required to avoid injury. If the contaminants present in the hazardous zone are particulate, vaporous or biological a very high degree of filtration will be required. If the personnel need to be mobile whilst carrying out operations the respirator will need to be portable and light. Providing enough air for breathing whilst overcoming high grade, high resistance filters requires a fast-acting flexible air delivery system.
This type of application uses technology first developed for hospital ventilators. The CPAP blower operating on low voltage DC, has the capability to deliver high volume flows from its compact size with a fast response time.
Another application of this type of fan is in the treatment of breathing conditions such as sleep apnoea. Using the CPAP blower to assist breathing whilst asleep reduces the risk of the ill effects sleep apnoea can cause.
For more details on the product ranges that are used in the health care industry please visit the ebm-papst web page as follows: https://www.ebmpapst.com/en/overview-industries/medical_laboratory-technology/medical_and_laboratory_technology.html?_ga=2.255489867.2137866670.1558524620-1479061727.1521445904