In addition to the fixed measuring poles located at each desk location, a range of hand held monitoring devices were utilised to provide a spot value assessment of the general research area during the 5-day 24x7 period. The following environmental equipment was deployed at both research locations:
3.9.1 Heat Stress Meter
The Extech HT30 Heat Stress meter was selected to measure 4 specific readings during five different periods throughout the day. Chapter 4 provides a review of the data captured. This device was used to compare readings against the environmental monitoring poles and the general area temperature and humidity devices. The device is normalised for external use (full sun) or internally (no sun) and possess four measuring parameters.
This particular temperature & humidity meter, provides an overall validation of the area being monitored, but it also provides black globe measurements to assess the overall temperature inclusive of contributory surrounding radiant factors.
Black Globe Temperature & Humidity Meter Specification Wet Bulb Globe Temperature (WBGT) range 0- 50 deg.C
WBGT accuracy Calculated from other factors (see eq…)
Black Globe Temperature (Tg) range 0 – 80 deg.C
Tg accuracy (Indoor) +/- 2 deg.C
Air Temperature range (Ta) 0 – 50 deg,C
Ta accuracy +/- 1 deg.C
Relative Humidity (RH) 0 – 100%
RH accuracy +/- 3% at 25 deg.C (10 - 95%)
Resolution 0.1 deg.C / 0.1% RH
Operating Temperature 0 – 50 deg.C
Operating Humidity 80% RH
Manufacturers Data
http://www.extech.com/instruments/product.a sp?catid=37&prodid=158
Table 32 - Black Globe Temperature Meter Characteristics
The Wet Bulb Globe Temperature (WGBT) or heat stress index indicates how hot the environment feels when humidity is combined with temperature, air movement, and sunlight.
𝑊𝐵𝐺𝑇 = 0.7𝑇𝑤 + 0.2𝑇𝑔 + 0.1𝑇𝑎
Tw = wet bulb temperature (Humidity and (Ta) air temperature combined) Tg = black globe temperature (Mean Radiant Temperature MRT)
Ta = Normal air temperature (The kinetic or motion energy within air)
Air temperature (Ta) is a measure of how warm a volume of air has reached, and indicates the kinetic or motion energy within a given volume of air.
Relative Humidity (RH%) is the amount of water vapour present in air expressed as a percentage of the amount needed for saturation at the same temperature. If the air is at 100-percent relative humidity then sweat will not evaporate into the air. As a result, we feel much hotter than the actual temperature when the relative humidity is high.
Relative humidity is an important characteristic for thermodynamic heat transfer.
Black Globe Air Temperature (TG) or Mean Radiant Temperature measures the contributory effect of radiant heat from the immediate surroundings, but remains a factor of air temperature. The MRT is a contributory measure and calculated value using the following expression;
𝑀𝑅𝑇 = [(𝐺𝑇 + 273)4+ 1.1 𝑥 108𝑥 𝑉𝑎0.6
∈ 𝑥 𝐷0.4 (𝐺𝑇 − 𝑇𝑎)]
1/4
− 273
MRT = mean radiant temperature (°C) GT = globe temperature (°C) - measured Va = air velocity at the level of the globe (m/s) ε = emissivity of the globe (no dimension) D = diameter of the globe (m)
Ta = air temperature (°C)
The use of the heat stress meter facilitates a more accurate understanding of how MRT relates to the way we need to consider how the human body dissipates heat.
The human body dissipates heat through 4-primary means:
1) Varying the rate and depth of circulation;
2) The sweat glands
3) Through the skin as sweat or perspiration 4) The respiratory system through exhalation.
Heat loss via the skin accounts for <90% of the bodies heat loss, therefore it is important to provide a thermal exchange mechanism between the occupants body and that of the surroundings. Sweating on its own is not an efficient mechanism as it relies upon evaporation, and during periods of high relative humidity evaporation is constrained by the humidity within the surrounding air. Heat is also exchanged trough breathing, as the lungs act as an internal liquid to air heat exchanger. The sensors utilised on the EMP’s however, only measured air temperature (Ta) and consequently the use of the Heat Stress meter was considered an appropriate means to verify any correlations.
3.9.2 Sound Power Meter
The Extech SDL 600 Sound Power level meter was selected to measure the overall sound level. Selecting frequency weighting “A” as defined within IEC 61672 was selected, we reflect more closely the ears interpretation of noise and therefore we can align our measurements with occupant survey responses. The use of an “A” weighting and “Fast”
response noise setting is commonly used when assessing environmental
noise levels, particularly when instantaneous peaks may occur within a workplace environment. The device was located within the centre of the room and configured with 120s recording interval and 24x7 operation. Table 34 indicates the meter specification.
Noise Meter Specification
Time Response Fast (125ms); Slow (1s) selectable
Sampling Rate Auto (120); 1, 2, 5, 10, 30, 60, 120, 300, 600, 3600s Applicable Standards IEC 61672-1: 2002 Class 2; ANSI S1.2: 1983 Type 2 Operating Temp Range 0 – 50 deg.C
Operating Humidity 85% RH (max)
Manufacturers Data http://www.extech.com/instruments/product.asp?catid=18&prodid=
680
Table 33 - Extech Noise Meter Specification Details
3.9.3 CO
2Humidity Temperature Data Logger
The Extech SD 800 CO2/Humidity/Temperature data-logger was selected to monitor the overall research area.
This selection provided a comparative measure against the data loggers located on the EMP’s. The unit is provided with a separate plug and play CO2 sensor but has an internal temperature & humidity sensor. The meter was configured with a 120s recording interval and continuous recording 24x7 for the duration of the site. Table 35 indicates the meter specification.sit.
Table 34 - Extech CO2/Humidity/Temperature Meter Specification Details
CO2 Humidity & Temperature Meter Specification Temperature sensor
Relative Humidity sensor Precision Capacitance Type
CO2 Sensor NDIR (Volume)
Temperature sensor range 0 – 50 deg.C (resolution 0.1 deg.C) Relative Humidity sensor range 10 – 70 – 90 % (resolution 0.1%)
CO2 Sensor range <1000 - <3000 - >3000ppm (resolution 1ppm) Selectable Data Sampling rate Auto, 5, 10, 30, 60, 120, 300, 600s
Temperature sensor accuracy +/- 0.8 deg.C Relative Humidity sensor accuracy +/- 4%
CO2 Sensor accuracy <1000 (+/- 40ppm); <3000ppm (+/-5%);
>3000ppm (+/- 250ppm) Operating Temperature 0 – 50 deg.C
Operating Humidity <90%
Manufacturers Data
http://www.extech.com/instruments/product.asp?catid=3 7&prodid=628
3.9.4 Illumination (Light Meter)
The SDL 400 light meter was selected to provide a general horizontal Illuminance, and was located within the centre of the research area with close proximity to the environmental poles. The horizontal Illuminance is assessed against the vertical Illuminance levels measured on each environmental monitoring pole and is compared to standard UK and global guidelines. The unit of measure selected is the “Lux” which reflects the current industry standards referenced within Chapter 2. The meter was configured for 120s recording
interval and 24x7 operation. Table 35 indicates the meter specification.
Table 35 - Extech SD 400 Light Meter Specification Details
3.9.5 TSI Particulate Meter
As part of an overall IEQ assessment approach, air quality is a fundamental aspect to consider and to investigate. To investigate further the air quality within each research site, the TSI 9306-02 was hired form BSRIA Hire Solutions Ltd. The unit sample size ranged form 0.3; 0.5; 1.0; 3.0; 5.0; 10 μm and the unit was configured to operate 24x7. The meter was set up with a ∞ infinite time sampling period, a sample period of 60s and a hold interval period of 120s. The
data was extracted using the OEM software to an xls format to allow correlation of the data across other independent IEQ variables. The device uses a light scattering laser diode light source to measure the particulates drawn into the unit using an internal vacuum pump and Isokinetic sampling probe.
Illumination (Light) Meter Specification
Sensor Types Colour corrected dome type CIE compliance Sampling Rate Auto, 1, 2, 5, 10, 30. 60, 120, 300, 600 1800, 3600s Range <2000; <20,000; <100,000lux
Resolution <2000lux 1 lux Resolution <20,000lux 10lux Resolution <100,000lux 100lux
Accuracy +/-4%
Operating Temperature 0 – 50 deg.C Operating Humidity 85% max
Manufacturers Data http://www.extech.com/instruments/product.asp?catid=10&pro did=677