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Safe operation of laboratories

Requirements for the Technical Equipment

Safety and energy efficiency are today principal requirements for the ­technical equipment of labs. The safety of people in the workplace is of ­paramount importance and must be ensured at all times. This is particularly true for workplaces which are exposed to increased risks. This article ­describes the role of the ventilation and air conditioning technology in such an environment.

The new FSE automatic sash device for fume cupboards ensures that sashes that have been left open unintentionally will be automatically closed after a certain time. Users can comfortably open or close the sash by just pushing it lightly or else by pressing a button or actuating a pedal switch. The volume flow will be adapted to the sash opening, which results in less energy being consumed and at the same time perfect safety of the surroundings. The device can be retrofitted.

A chemical accident in a laboratory can quickly lead to a harmful or even life-threatening concentration of hazardous substances in the room air. This is why the ventilation and air conditioning system plays a key role in maintaining safe working conditions for the staff in a lab. In case of an incident it does not suffice to just open a window in order to let fresh air in. The air change rate is just one factor; other factors that need to be considered include turbulences, heat sources, face velocities, noise levels, and most of all the ever changing volume flows of fume cupboards and safety cabinets.

A bus connects the individual controllers. All fume cupboards in a room can be controlled using just one room control panel, and just one interface is required to integrate the system with the central BMS and to transmit the consolidated room data. Additional controllers and measuring points can be included in the room balance via a 0 V to 10 V signal. (All figures by TROX GmbH)

Air management system

The highest levels of safety can be achieved with an air management system. Such an air management system includes VAV terminal units with volume flow controllers that increase or reduce the extract air for each fume cupboard individually and depending on the overall situation. Based on the room pressure, volume flow controllers balance the supply air and extract air ratio without restricting the function of each fume cupboard. This results not only in a safe working environment but also in a reduction of the operating costs for the air conditioning system.

Removing hazardous substances from the air is the most important goal. At the same time, neighbouring compartments must also be protected from those hazardous substances.

Fume cupboards

Fume cupboards have a special function when it comes to protecting the staff in a lab. Three prime objectives are obvious:

1. Retention: Fume cupboards must prevent dangerous concentrations of gases, fumes or dusts from escaping the fume cupboard and being released into the lab.

2. Increased air change: Fume cupboards must prevent the development of an atmosphere that can ignite or even explode.

3. Splash and shatter protection: Fume cupboards must prevent spray or flying fragments from injuring people.

While splash and shatter protection is obviously ensured by the construction of a fume cupboard, the first two points require volume flow control. Even though there is a multitude of different applications and requirements for laboratories, today's control systems cover all common control strategies.

Control strategies

Air management systems can support various strategies regarding the control of supply air and extract air in rooms, of fume cupboards, and of room and duct pressure. An air management system combines control functions with energy management and monitoring functions and individual room operating modes.

//Room control

An air management system controls and balances the volume flows for various room scenarios and fume cupboards. Stable control requires that the actual volume flow rates are precisely measured and the setpoint values quickly be achieved or maintained.

// Differential pressure control

Differential pressure control for rooms or ducts can be included in individual control strategies. Cascade control rather than differential pressure control with a damper blade – without considering any special volume flow limits – allows for much more stable room situations even with quick-response volume flow control loops.

// Control for areas with potentially explosive atmospheres (ATEX)

For areas with potentially explosive atmospheres special components are available that fulfil the requirements of rapid response volume flow controllers, room pressure controllers, and fume cupboard controllers, including monitoring.

// Interface with the central BMS

Safety systems must be connected to higher-level building management systems. Such connections require flexible interfaces. In addition to analog inputs and outputs and switch contacts as a means of changing the operating mode and transmitting information, digital network communication can provide transparency yet requires very little wiring effort.

The central BMS can request the following information:

// Volume flow rate and room pressure setpoint and actual values

// Local faults

// Consolidated fault messages with configurable content

// Damper blade positions (optimised air management)

// Operating modes

// Sash position (for fume cupboard ­control)

// Face velocity (for fume cupboard control)

// Set fume extract level (for fume ­cupboard control)

The central BMS can preset the following parameters as defaults for the room or a fume cupboard controller:

// Operating mode

// Change of priority for operating mode default setting between the control ­panel and the central BMS

// Switching between two room ­pressure setpoint values

// Volume flow rate setpoint change ­signals (external temperature and ­pressure control)

Reducing costs by saving energy

Supply air and extract air volume flows must comply with national and international standards regarding safety in the workplace and protection of the environment. As a consequence, air management is of central importance when energy consumption and operating costs shall be reduced. An air management system ensures a high level of energy efficiency due to the demand-based volume flow control.

Fume cupboard control – quick-response control

While the common variable air volume controllers react within approximately 120 s, controllers developed for the ventilation of laboratories react within only 3 s. These rapid response times ensure that no outbreak of hazardous substances can occur, e.g. in fume cupboards with variable, demand-based extract air. For slave control loops, these rapid response times enable stable room situations that ensure room pressure conditions according to DIN 1946, part 7. Dedicated actuators move the damper blades such that the setpoint value is reached quickly and precisely.

L&M orient 1 / 2014

The articles are publishes in issue L&M orient 1 / 2014.
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