GB2190184A

GB2190184A - Measuring air change rate in a room

Info

Publication number: GB2190184A
Application number: GB08611123A
Authority: GB
Inventors: John Peter Lilly; Rodney Gale
Original assignee: British Gas PLC
Current assignee: British Gas PLC
Priority date: 1986-05-07
Filing date: 1986-05-07
Publication date: 1987-11-11
Also published as: GB8611123D0

Abstract

An apparatus for measuring the air change rate in a room which is completely portable and self- contained, includes a source 3 of SF6 tracer gas, infrared means 6 for measuring the concentration of the tracer gas after release into the room, and a microcomputer 7 adapted automatically to control the measuring means to measure the tracer gas concentration at predetermined time intervals, to record those concentrations and then to calculate the rate of air change using the concentration. The apparatus can measure the air change rate in several rooms simultaneously using remote sampling lines. <IMAGE>

Description

SPECIFICATION Method of and apparatus for measuring air change rate in a room The invention relates to a method of and apparatus for measuring air change rate in a room.

Previous methods and aopparatus have required labour intensive installation of extensive equipment by skilled staff. Such equipment is not compact, is cumbersome, and is expensive to install and operate.

It is accordingly among the objects of the invention to seek to mitigate these disadvantages.

According to one aspect of the invention there is provided a method of measuring the air change rate in a room, comprising the steps of releasing a tracer gas into ambient atmosphere in the room, providing means for measuring the rate of decay of the tracer gas in the ambient atmosphere, and providing a computer device which automatically controls the measuring means to measure and record the tracer gas concentration at a predetermined time to record the concentration and then to calculate the rate of air change using the recorded concentration.

The step of calculating the rate of air change may be carried out when the tracer gas value has fallen to a predetermined percentage of its initial concentration.

The concentration may be less than 20% of the initial concentration.

The step of calculating the rate of air change may be carried out after a predetermined time period if the concentration has not fallen to below a predetermined percentage of its initial value.

The time period may be one hour and the predetermined percentage may be 20%.

The method may include the step of providing a visual record of the rate of air change.

The air change rate for each of a pluraility of separate rooms may be simultaneously monitored and calculated by the computer device.

According to a second aspect of the invention there is provided apparatus for measuring the air change rate in a room, comprising a source of tracer gas, means for measuring the rate of decay of the tracer gas when released in the ambient atmosphere in the room from the source, and a computer device adapted automatically to control the measuring means to measure the tracer gas concentration at a predetermined time interval to record the concentration and then to calculate the rate of air change using the recording concentration.

There may be a single device including the source, measuring means and computer device.

The device may comprise means for visual display of the rate of air change.

The visual display means may comprise a liquid crystal display. This provides a direct reading.

The visual display means may comprise a chart or printer. This arrangement may provide a hard copy.

The apparatus may include means for simultaneously measuring and recording tracer gas decay from each one of a plurality of remote rooms. This system enables the air change rate for a whole building to be monitored, for example.

The said means may comprise a sample valve connectible with a plurality of sample lines each to a respective one of the remote rooms.

The source of tracer gas may comprise a bottle of SF6 gas.

The measuring means may comprise an infra-red detector.

The apparatus may include one or more carrying handles. This construction renders the apparatus self-contained and portable.

It will be understood that the invention extends to a room or rooms in which the air change rate is measured using a method or apparatus as hereinbefore defined.

A method of, and apparatus for, measuring the air change rate in a room are hereinafter described by way of example, with reference to the accompanying drawings.

Figure 1 is a schematic view of one apparatus according to the invention for measuring the air change rate in a single room; Figure 2 is a perspective view of a second apparatus, according to the invention, for simultaneously measuring the air change rate in each one of a plurality of remote rooms; Figure 3 is a schematic view of the apparatus of Fig. 2; Figure 4 is a schematic signal conditioning circuit for the apparatus for Figs. 1 and 2; Figure 5 is a schematic representation of typical signal shapes for the conditioning stages shown in Fig. 4; Figure 6a, 6b and 6c show a flow chart of operating sequences for the apparatus of Fig. 1 and of Figs. 2 and 3; and Figure 7 is a schematic microcomputer system for controlling the apparatus of Figs. 2 and 3.

In the drawings like parts are indicated by like numerals.

Referring firstly to Fig. 1, the apparatus 1 shown therein is a single portable device or body 2 housing a source of tracer gas in the form of a bottle 3 of SF6 with two pressure gauges 4 and 5 a means 6 of measuring the rate of decay of the tracer gas when released from the bottle 3 and injected into the ambient atmosphere of a room in which the apparatus 1 is situated, and a computer device 7 in the form of a microcomputer which automatically controls the measuring means, in this case an infra-red detector 6, to measure the tracer gas concentration at a predetermined time interval, which automatically records the concentration and then calculates the rate of air change using the recorded concentration. The microcomputer 7 includes visual display 8 in the form of a liquid crystal display and allows for chart recorder and printer output.

There is a fan 9 which injects the SF6 tracer gas into the ambient air 10 of the room when released from the bottle 3. There is a self-contained power supply 11, fed from the mains 12 in use.

The detector 6 is an open infra-red detector within a perforated section 13 of the body 2 of the apparatus 1.

Referring now to Figs. 2 and 3, the apparatus 14 shown therein is similar to that of Fig. 1, except that there are sample valves 15 and means 16 for connection of those valves with remote sampling lines 17 which each extend to the apparatus 14 from a single respective one of a plurality of remote rooms (not shown) whereby the rate of air change in those rooms is automatically simultaneously monitored, recorded and displayed. There is a sample pump 18 and exhaust pipe 19, and carrying handles 20 whereby the apparatus 14 is rendered portable.

Figs. 4 and 5 show schematically respectively a signal conditioning circuit 20 and signal shapes 21 for the apparatus of Figs. 2 and 3.

In Fig. 4, there is shown series connections between the detector 6, first operational amplifier 22, rectifier 23, smoothing filter 24, second operational amplifier 25, analogue/digital converter 26 and microcomputer 27, the connections being designated as A,B,C,D and E and shown in Fig. 5, in a plot of voltage against time for each one. At connection A, the complex signal range input to the first operational amplifier 22 is shown, which operational amplifier 12 amplifies the signal as shown at connection B. This signal is then rectified in a bridge circuit of the rectifier 23 to provide a ramp D.C. signal as shown for connection C.

Connection D shows the signal smoothed by the filter circuit 24 to D.C., and connection E shows the D.C. signal further amplified by the second operational differential amplifier 25 to provide gas calibration and signal for reading by the microcomputer or microprocessor 27.

Figs. 6a, 6b and 6c show a flow chart 28 of operating sequences for both the apparatus 1 of Fig. 1 and for that 14 of Figs. 2 and 3. In Fig. 6, as shown by the key, the plain boxes are automatically controlled operations and those with heavy edging are manual operations. Going through the chart 28 in sequence, on start-up 29, the mains 30 is switched on manually after the apparatus 1 or 14 is plugged in and this provides power to the infra-red detector so that it warms up 31. The tracer gas is then turned on 32 at the bottle 3 and the pressure is set using the gauges 4 and 5.

The sample lines are run as required 33.

Henceforth, the sequence is completely automatic. There is a fifteen minute wait 34 for warming up the infra-red detector 6, then the microcomputer switches on power to the chart recorder 35 and the sample pump is switched on 36 by the microcomputer 7 which then takes and stores a reference reading 37 of the background tracer gas present in the ambient atmosphere of the room or rooms (Co). The mixing fan 9 is then switch on automatically 38 (after 20 mins) to mix the tracer gas in the room. Then the microcomputer automatically waits 5 minutes on injecting the tracer gas 39, so that after 25 minutes the tracer gas injection valve is turned off 40 and for one minute more the gas is mixed 41 before the fan is automatically stopped 42.

The sampling sequence is now commenced 43 with an initial concentration reading 43a, which is stored. A reading of tracer gas concentration is then taken every 30 seconds and stored 44 (with optional display on the chart recorder). If the concentration is less than 80% of the original concentration, 45, route 46 is followed so the microcomputer automatically performs an air change rate calculation 47 and displays the result 48. If the concentration is not less than 80% at 45, the microcomputer automatically waits 30 seconds 49 then works out if one hour has elapsed since intial reading 50. If one hour has not elapsed, route 51 is followed and functions 44, 45 are performed again.

If there is inadequate decay of the tracer gas, the air change rate, or in other words the ventilation rate of the room, calculation is thus carried out as shown by many repeats of route 51. Route 46 shows the sequence of operation where there is an adequate decay of tracer gas.

It will be understood that where the apparatus of Figs. 2 or 3 is used to calculate simultaneously the air change rate of a number of individual, remote rooms, the sequence starting at 43a applies. Thus say ten channels can be stored simultaneously, sampling of the decay rate being in a rotational sequence.

In either embodiment the apparatus computes the air change rate based on alternate calculations, viz either decay of tracer gas concentration over time intervals to a percentage which in the embodiments described is less than 20% of the original, or on a time basis from start of operational sequence namely one hour as described.

In either embodiment, the microcomputer calculates the tracer gas decay rate using the following formula: Q= 1 (1n (C1-Co)-1n (C2-Co)) t2-t1 where Q=Air change rate (air changes per hour) t1 time of reading C1 hours t2=time of reading C2 hours Co=ambient concentration (background reading) Cl =initial concentration measurement at t1 C2=final concentration measurement at t2 Fig. 7 shows a system for controlling the apparatus of Figs. 2 and 3 and includes the microcomputer or processor 7, read only memory (ROM)52, random access memory (RAM) 53 and real-time clock or time base 54 connected with a system bus 55 to which is also connected the analogue -to- digital converter 26 control relays 57, display 58 and printer 59 via the input/output parts 60.

In summary it will be understood that in the method and apparatus of Fig. 1, in the Microprocessor controlled SF6 decay measuring device there is Automatic sequence control injects ) -from gas bottle mixes ) -with fan samples ) -via open l.R. cell.

SF6 detection by means of an open infra-red cell within a perforated section of instrument case.

Microprocessor 1) Monitors decay as measured by the l.R. detector cell with respect to ambient readings.

2) Controls all necessary sequence functions.

3) Outputs to L.C.D. display and chart recorder (hard copy).

in the method and apparatus of Figs. 2 and 3, the method and apparatus is as above but includes: -Closed cell SF6 infra-red detector -additional computer interface controlling up to 10 sample inlets -printed output for all 10 channels -independent mixing terminals for each channel (optional) -may not include automatic injection of tracer gas.

Thus the invention above described utilises an on board microcomputer or microprocessor 7 to perform necessary logarithmic calculations on measured and recorded data to produce a single value read-out of air changes per hour (or other air change rate) at the end of decay of the tracer gas.

Claims

1. A method of measuring the air change rate in a room, comprising the steps of releasing a tracer gas into ambient atmosphere in the room, providing means for measuring the rate of decay of the tracer gas in the ambient atmosphere, and providing a computer device which automatically controls the measuring means to measure and record the tracer gas concentration at a predetermined time to record the concentration and then to calculate the rate of air change using the recorded concentration.

2. A method according to Claim 1, the step of calculating the rate of air change being carried out when the tracer gas value has fallen to a predetermined percentage of its initial concentration.

3. A method according to Claim 2, the concentration being less than 80% of the initial concentration.

4. A method according to Claim 1, in which the step of calculating the rate of air change is carried out after a predetermined time period if the concentration has not fallen to below a predetermined percentage of the initial value.

5. A method according to Claim 4, the time period being one hour and the predetermined percentage being 20%.

6. A method according to any preceding claim, including the step of providing a visual record of the rate of air change.

7. A method according to any preceding claim, in which the air change rate for a plurality of separate rooms is monitored and calculated by the computer device.

8. A method of measuring the air change rate in a room, substantially as hereinbefore described with reference to the accompanying drawings.

9. Apparatus for measuring the air change rate in a room, comprising a source of tracer gas, means for measuring the rate of decay of the tracer gas when released in the ambient atmosphere in the room from the source, and a computer device adapted automatically to control the measuring means to measure the tracer gas concentration and then to calculate the rate of air change using the recorded concentration.

10. Apparatus according to claim 9, comprising a single device including the source, measuring means and computer device.

11. Apparatus according to Claim 10, the computer device comprising a microprocessor.

12. Apparatus according to Claim 11, the device comprising means for visual display of the rate of air change.

13. Apparatus according to Claim 12, the visual display means comprising a liquid crystal display.

14. Apparatus according to claim 12, the visual display means comprising a chart or printer.

15. Apparatus according to any of Claims 9 to 14, including means for simultaneously measuring and recording tracer gas decay from each of a plurality of remote rooms.

16. Apparatus according to Claim 15, said means comprising a sample valve connectible with a plurality of sample lines each to a respective one of the remote rooms.

17. Apparatus according to any of Claims 9 to 16, the source of tracer gas comprising a bottle of SF6.

18. Apparatus according to any of Claims 9 to 17, the measuring means comprising an infrared detector.

19. Apparatus according to any of Claims 9 to 18, including one or more carrying handles.

20. Apparatus for measuring the air change rate of a room, substantially as hereinbefore described with reference to the accompanying drawings.

21. A room or rooms in which the air change rate is measured using a method according to any of Claims 1 to 8 or apparatus according to any of Claims 9 to 21.