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Aquilar - Leak Detection Design Guide

Refrigerant Leak - Leak Detection Design Guide - Sensor Selection

Design Guide –
AquiTron Refrigerant Gas Detection

Whether you are designing a refrigerant gas (air conditioning gas) leak detection system for a hotel, an apartment building, office space, concert hall or public building, gas leaks and emissions are a concern.

You should ensure that your systems are safe, that adequate monitoring is in place and that you are complying with regulations whilst still keeping costs under control.

There are many different worldwide standards, however, the main reason for detection of gas is to protect personnel, protect the environment and save costs.

For reference, the standards in the UK and parts of Europe are:

F-Gas Regulations, BS EN 378 and BREEAM Pol 01.

Exposure Limits

Refrigerant gas manufacturers supply MSDS and COSHH data sheets that typically state 1000ppm for an 8-hour period which is a time weighted average (TWA).

When Do I Need Refrigerant Detection?

There are guidelines on the maximum volume of refrigerant that could be discharged into a space without the need for a fixed refrigerant sensor, also known as “practical limits”. These two examples have been taken from BS EN 378 Part 1 and have been widely used for air conditioning applications for hotel bedrooms and small office spaces.

For example the value 0.42kg/m³ is for R410A, (QLMV) contact us for other gases. Above this value a sensor is required. Other international standards use similar values as a guide.

How Many Sensors Do I Need?

In many applications, such as small offices and hotel rooms, one sensor mounted at low level will provide the desired level of protection. This does depend on the size of the room and the quantity of air conditioning units. There are no published regulations or standards to help with this.

There have been various “good practices” and “good rules of thumb” which engineers have used in the past:

  • One sensor for every 36m² of floor area
  • One sensor for each air conditioning unit within the space

These guides typically do not apply to chiller and plant rooms.

Where Should Sensors be Placed?

The ability of a system to detect / measure the refrigerant leak is dependent on the location of the sensor. The sensor may be remotely located up to 100 metres from the controller. The controller and sensor should be firmly mounted indoors. The controller should be in an area where the display is easily seen.

The sensor location should be approximately 200 to 300mm above the floor in an area where refrigerant vapours are most likely to accumulate. Sensors should be in low-lying areas for occupant safety, or near each potential leak source if refrigerant conservation is a high priority, such as ceiling voids.

Systems used to protect personnel should have their sensors located in such positions that they monitor the concentration at heights of the occupants, considering the characteristics of the refrigerant used e.g. at less than bed height with heavier than air gases in a hotel room.

BS EN 378 states that a ceiling void is regarded as part of the human occupied space, unless it is airtight. Therefore monitoring in ceiling voids would not be acceptable.

Systems shall operate a supervised and/or audible and visual alarm so that appropriate action may be taken by the occupants or initiated by trained personnel and/or shall close the fractured refrigerant line by suitable valves to limit the rise in concentration within the human occupied space. In chiller rooms and plant rooms, these sensing points should be considered:

  • Low level close to the chiller
  • Pressure vent line (monitoring leaks from the safety valve)
  • Extract duct

Design Guide –
AquiTron & TraceTek Leak Detection

AquiTron and TraceTek leak detection systems can be utilised in a variety of installations to detect water, chemical or fuel leaks. TraceTek sensor cables detect and locate leaks along their entire length. AquiTron water sensing probes detect leaks at a specific point. Virtually any number of point sensors can be combined with sensor cables on a leak detection single circuit. The following information is provided for initial guidance only. Complete product information, including selection guides, data sheets, installation instructions and operating manuals can be downloaded from our website.

Sensor Selection

The first design task is to select the most appropriate sensor type based on the liquid to be detected and the area to be monitored.

Water Detection

AT-PROBE should be selected for areas requiring only a single point of detection, such as lift pits, drip trays under HVAC units and plant rooms.

TT1000 sensor cable should be selected for areas in commercial building applications where larger area coverage is required, such as under raised floors in computer or telecomms rooms, in building service / utility areas etc.

TT1100-OHP sensing cable has been specially designed for suspended piping applications where the cable is attached to the bottom of the pipe.

Fuel Oil Detection

TT5000 sensor cable should be selected for fuel and oil detection, such as diesel used in generators.

AT-OPSEN optical sensor probe should be selected for areas requiring only a single point of detection, such as lift pits, below diesel tanks and generators.

Sensor Layout

The next design task is to determine the optimum sensor layout. The sensing cable or point probe should be positioned so that leakage from the potential leak sources will contact the sensor quickly, before reaching any critical equipment, cables or other items to be protected.

Alarm Module Selection

Depending on the size of the leak detection system and accessibility of the sensors, an appropriate alarm (or alarm and locating) module must be selected.

Small Area Circuits for small leak detection circuits (normally those less than 30 metres of sensor cable in a single area), a simple alarm module may be selected. The EcoLeak ECO-1 and AT-SZA modules provide local indication of the system operating status via LEDs, plus voltage-free contacts for remote connection to external alarm signals, remote alarm panels, water shut-off valves or building management systems. Multi Zone panels (AT-MZA and Eco-6) allowing up to 8 different rooms to be monitored on one panel.

Large Circuits, Concealed Sensors or Separated Areas for large circuits (normally more than 30 metres or where sensors are distributed between several separate areas) or installations where the sensor is concealed and normally inaccessible, an alarm and location module is most appropriate. The digital TTDM-128 or TS-12 panel provides voltage-free alarm contacts and digital communication via simple RS-485 wiring and the ModBus RTU protocol. Alternatively, TTSIM modules can be connected either to the TTDM-128/TS-12 or directly to a building management system via RS-485 wiring. The TTSIM supports ModBus directly, providing complete sensor status and leak location information digitally to the host system. The TTDM-128 can be connected to as many as 128 TTSIMs via a single RS-485 network, allowing extremely large leak detection systems to be easily configured and integrated.

Click the PDF image to view the technical information in full

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