Work Package 2: Performance of naturally ventilated buildings

Transcription

1 Work Package 2: Performance of naturally ventilated buildings Detailed Monitoring Report BRE Energy Efficient Office of the Future (GB1) M K White, M Kolokotroni, R Shaw, J Pike, C Ni Riain and MDAES Perera Building Research Establishment Indoor Environment Division Table of contents 1. INTRODUCTION THE BRE ENERGY EFFICIENT OFFICE OF THE FUTURE ENVIRONMENTAL MONITORING Summer Winter RESULTS OF THE ENVIRONMENTAL MONITORING Room Room NIGHT VENTILATION CONCLUSIONS...11

2 1. Introduction Natvent TM is a Pan-European research project aimed at providing solutions to technical barriers which prevent the uptake of natural ventilation and low energy cooling for office-type buildings in countries with moderate and cold climates. It will also encourage and accelerate the use of natural ventilation and smart controls as the main design option in new designs and major refurbishment s. As part of the project and to gain a better understanding of the applicability and limitations of natural ventilation strategies, nineteen buildings, purposely built to incorporate a low energy ventilation strategy, are being studied in seven European countries. Of these the BRE Energy Efficient Office of the Future is one of three buildings being studied in the UK. This is a naturally ventilated building combining stack ventilation with automatic control to draw air through the building via ducts built into the sinusoidal ceiling slabs on the first and ground floor. Within Natvent TM a monitoring protocol has been developed so that a basic assessment of the ventilation strategy can be carried out with the minimum of monitoring; typically one week in summer and winter. During winter, the main focus is to examine whether acceptable indoor air quality (IAQ) is provided and whether the airflow rates are kept within a reasonable range to (a) avoid discomfort due to draughts and (b) minimise excess energy required to heat incoming air. In the summer the assessment focuses on whether comfort temperatures are established and whether maximum exchange of heat between the building structure and the outside air is achieved, during the day or especially at night when the outside is relatively cold. In summer, the control of air flows on its own is not so important so long as it does not result in excessively draughty conditions. The following parameters were measured: Internal and external CO 2 concentrations (to be used as the main general indicator for IAQ assessment), Internal and external water vapour levels (to be used as a secondary indicator for IAQ assessment), Fresh air flow rates, local wind speed and direction (to evaluate the fresh air provided), Internal and external air temperature and internal globe temperature (to assess thermal comfort). Fresh air flow rates are difficult to measure continuously in naturally ventilated spaces. This has been addressed in the NatVent tm project by the use of the constant concentration technique. This technique involves the use of automated equipment to inject tracer gas into the spaces being monitored to a specified concentration and to maintain this concentration throughout the period of interest. The level of fresh air entering the space can be calculated by measuring the amount of gas required to be injected to maintain the required concentration level. As the concentration of tracer gas is kept the same in all the spaces, the air flow rate consists only of that coming from outside. BRE Energy Efficient Office of the Future (GB1) 2/11

3 2. The BRE energy efficient office of the future The BRE Energy Efficient Office of the Future (Figure 1) was designed by Fielden Clegg Design. It is a three-storey building with the long axis running east-west, the west wall connects to an atrium forming the entrance hall. The ground and first floors comprise open plan and cellular offices and the second floor is large open plan office. On the ground floor there is a large lecture theatre to the north. This is connected to the main building by a circulation zone containing toilets and a display area. The western end of the main building contains, on the ground floor, a kitchen and buffet area and on the first and second floor toilets and seminar rooms. The building is naturally ventilated. The ceiling slabs contain ducts that open into the building over a nominal corridor zone bounded on one side by the walls of the north facing cellular offices and on the other by the open plan area. The windows on the external facades open either into a duct or, on the north facing wall into a cellular office, or, on the south facing wall into the open plan office. On the south side of the building are ventilation stacks which act to drive ventilation especially when there is insufficient wind, Figure 2. The openable windows are automatically controlled by the building management system, or can be operated by the occupants, and are used to ventilate the building during the day and at night operate as part of the night cooling strategy. In the north facing cellular offices there are openable windows and on the third floor there are openable windows on both north and south faces. The ventilation stacks have fans fitted to assist in purging the building for night cooling or to enhance daytime ventilation. Solar shielding is provided by automatically controlled louvres on the south-facing facade. Extra cooling can be provided if necessary by using ground water. Figure 1: External view of the BRE Energy Efficient Office of the Future The internal design conditions are: For winter, 18 o C minimum internal temperature, For summer the design criteria is, 25 o C is not to be exceeded for more than 5% and 28 o C is not to be exceeded for more than 1% of the year. BRE Energy Efficient Office of the Future (GB1) 3/11

4 Figure 2 Ventilation strategy All other criteria, % RH, CO 2 etc should be within acceptable ranges, ie good practice. The maximum design ventilation rate is 1 h Environmental monitoring 3.1 Summer Summer monitoring of the BRE Energy Efficient Office of the Future was carried out in August 1997 in two offices located on the first floor, see Figure 3. The offices are on the north side of the building, one central and the other at the eastern end of the floor. The offices were single occupancy, the central office (Room 1) had space for meetings and had a floor area of about 31 m 2, the other (Room 2) was of more conventional size at about 17 m 2 floor area. Room 1 Room 2 corridor zone Atrium Open plan N Ventilation stacks Figure 3: First floor, floor plan showing monitored offices BRE Energy Efficient Office of the Future (GB1) 4/11

5 3.2 Winter Winter monitoring in the building took place in January The same two offices were monitored during this period. 4. Results of the environmental monitoring 4.1 Room 1 Air change rate Winter: Figure 4 shows air change rates in both rooms during the winter monitoring period. The values for Room 1 peak at about 6.5 h -1, with an average of.78 h -1. The periods of high ventilation rate tend to coincide with periods of occupancy. An analysis of wind speed and direction data and the background air flow rates does show some correlation between higher ventilation rates and wind directions between 1 o and 25 o. Summer: Figure 5 shows air change rates for both rooms. The values for Room 1 peak at about 3 h -1, with an average of 3.3 h -1. The high values of air change rate are probably due to poor mixing occurring at times when the windows were open, there were many occasions when the measured ventilation rate exceeded 1 h -1. Most of the periods of high ventilation rate coincide with occupancy. An analysis of the wind speed and direction data showed come correlation of increasing ventilation with increasing wind speed. There was also a weak correlation between ventilation rate and wind direction, winds from the directions 2 o to 33 o tended to coincide with higher ventilation rates Air change rate (1/h) : 1/8/ : 1/1/ : 1/12/ : 23: 1: 3: 5: 7: 9: 11: 14/1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/1998 Room 2 ach Room 1 ach Figure 4: Winter, air change rate in the monitored rooms BRE Energy Efficient Office of the Future (GB1) 5/11

6 Air Change Rate (1/h) /7/ :24 2/8/ :19 6/8/ :53 8/8/ :57 1/8/ :52 13/8/1997 1:22 15/8/ Room 1 Room 2 Figure 5: Summer, air change rates in the monitored rooms Carbon dioxide and relative humidity Winter: Figure 6 shows CO 2 levels for both rooms. The concentrations for Room 1 peaked at 125 ppm on one occasion when the room was occupied. At other times concentrations were generally below 1 ppm Carbon dioxide (ppm) : 1/8/ : 1/1/ : 1/12/ : 23: 1: 3: 5: 7: 9: 11: 14/1/199816/1/ /1/ /1/ /1/199825/1/ /1/ /1/1998 External CO2 Room 2 CO2 Room 1 CO2 Figure 6: Winter, carbon dioxide concentration in the monitored rooms Figure 7 shows relative humidity for both rooms. In Room 1 %RH was generally between 45 to 3 %, which is acceptable, however, there were a small number of occasions where %RH fell below 3 %. BRE Energy Efficient Office of the Future (GB1) 6/11

7 1 9 8 Relative humidty (%RH) : 1/8/ : 1/1/ : 1/12/ : 23: 1: 3: 5: 7: 9: 11: 14/1/ /1/ /1/ /1/ /1/ /1/ /1/ /1/1998 Room 2 %RH Room 1 %RH External %RH Figure 7: Winter, relative humidity in the monitored rooms Summer: Figure 8 shows CO 2 levels for both rooms. Concentrations for Room 1 peaked at just under 8 ppm on two occasions during occupancy, generally concentrations were well below 6 ppm. On several occasions the concentrations for internal and external locations were similar, this is probably due to an open door adjacent to the external sample location being left open allowing internal air to spill out over the sample line and be sampled. 9 Carbon dioxide concentration (ppm) /7/ :21 2/8/ :16 6/8/ :5 8/8/ :54 1/8/ :49 13/8/1997 1:19 15/8/ :23 External Room 1 Room 2 Figure 8: Summer, carbon dioxide concentrations in the monitored rooms Figure 9 shows relative humidity for both rooms. In Room 1 %RH levels were generally between 55 and 65 % and peaked at just under 7 %. BRE Energy Efficient Office of the Future (GB1) 7/11

8 Relative humidity (%RH) /7/97 16:24 2/8/97 8:17 4/8/97 :18 7/8/97 1:49 9/8/97 2:5 1/8/97 18:52 12/8/97 1:53 14/8/97 17:47 External %RH Room 1 %RH Room 2 %RH Figure 9 Summer, relative humidity levels in the monitored rooms Temperatures Winter: Figure 1 shows air and globe temperatures for both rooms and external temperature. In Room 1 temperatures were above the design minimum value generally by between 2 to 5 o C. There is some evidence of heat gains giving rise to higher temperatures on some days Temperature (degc) :38:26 14/1/98 7:38:26 16/1/98 23:38:26 17/1/98 15:38:26 19/1/98 7:38:26 21/1/98 :29:28 23/1/98 16:29:28 24/1/98 8:29:28 26/1/98 :29:28 28/1/98 16:29:28 29/1/98-5 Room 1 air temp Room 1 globe temp Room 2 air temp Room 2 globe temp External temp Figure 1: Winter, air and globe temperatures in the monitored rooms BRE Energy Efficient Office of the Future (GB1) 8/11

9 Air Temperature (degc) /7/97 16:2 2/8/97 8:19 4/8/97 :2 7/8/97 1:5 9/8/97 2:5 1/8/97 18:49 12/8/97 1:5 14/8/97 17:5 External air temps Room 1 air temps Room 2 air temps Figure 11: Summer, air temperatures in the monitored rooms Summer: Figure 11 shows the temperatures for both rooms during summer and external temperature. In general, in Room 1, the 25 o C design value was exceeded on only three occasions and the 28 o C design maximum value was not exceeded at all. 4.2 Room 2 Air change rate Winter: Figure 4 shows air change rates in both rooms during the winter monitoring period. The values for Room 2 generally peak at about 7 h -1, with an average of.74 h -1.The periods of high ventilation rate tend to coincide with periods of occupancy. An analysis of wind speed and direction data and the background air flow rates does show some correlation between higher ventilation rates and wind directions between 1 o and 25 o. Summer: Figure 5 shows air change rates for both rooms. The values for Room 2 peak at about 7 h -1, with an average of 2.1 h -1. Most of the periods of higher ventilation rate coincide with occupancy. An analysis of the wind speed and direction data showed come correlation of increasing ventilation with increasing wind speed. There was also a correlation between ventilation rate and wind direction, winds from the directions 2 o to 33 o tended to coincide with higher ventilation rates. Carbon dioxide and relative humidity Winter: Figure 6 shows CO 2 levels for both rooms. The concentrations for Room 2 peaked at 15 ppm on one occasion when the room was occupied. At other times concentrations were generally about or below 1 ppm. Figure 7 shows relative humidity for both rooms. In Room 2 %RH was generally between 45 to 3 %, which is acceptable. Summer: Figure 8 shows CO 2 levels for both rooms. Concentrations for Room 2 peaked at about 55 ppm during occupancy, generally concentrations were about 45 ppm. BRE Energy Efficient Office of the Future (GB1) 9/11

10 Figure 9 shows relative humidity for both rooms. In Room 2 %RH levels were generally between 55 and 65 % and peaked at just less than 7 %. Temperature Winter: Figure 1 shows air and globe temperatures for both rooms and external temperature. In Room 2 temperatures were above the design value in general by between 2 to 5 o C. On one occasion the temperature dropped to about 16 o C. There is some evidence of heat gains giving rise to higher temperatures on some days. There was little difference between air and globe temperatures throughout the whole monitoring period. Summer: Figure 11 shows the temperatures for both rooms during summer and external temperature. In general in Room 2 the 25 o C design value was exceeded on only four occasions and the 28 o C design maximum value was not exceeded at all. 5. Night ventilation The Energy Efficient Office of the Future was occupied in June The night ventilation strategy using the stacks and windows under automatic control was in operation during the whole summer period. Figure 12 presents external and internal air temperatures on the first floor of the building during a hot week in August when external temperature exceeded 3 o C. Internal air temperatures, however, were maintained at less than 27 o C. The expected time lag between internal and external temperatures was observed indicating the effect of the heavy weight construction of the building incorporated mainly in the form of the sinusoidal exposed concrete ceiling. During the week presented in Figure 12, the fans in the stacks were initiated for one hour on Monday (1.am) and six hours on Tuesday (6.-12.) to increase flow rates as the internal temperatures were exceeding set points. Windows were opened every night mainly during the evening just after occupation, to naturally night ventilate the building. Ground water was not utilised for cooling during this period. Therefore, the achieved internal air temperatures are due to a combination of exposed thermal mass, day and night natural (fan assisted) ventilation, solar shading and minimisation of internal heat gains through the use of efficient artificial lighting and maximising day-lighting Air Temperature degc Wed : 7 Thu : 8 Fri : 9 Sat : 1 Sun : 11 Mon : 12 Tue : 13 Wed : Office External Figure 12: Summer, one week s external and internal air temperatures during August 1997 BRE Energy Efficient Office of the Future (GB1) 1/11

11 6. Conclusions The results of the monitoring indicate that the building design provides a generally comfortable indoor environment. In winter CO 2 and humidity levels are within acceptable values and comfortable temperatures were recorded with appropriate fresh air ventilation rates. During the summer period the measured temperature data indicate that the high thermal mass coupled with the night ventilation strategy and solar shading minimised internal heat gains to reduce the effect of external temperatures. In conclusion, the winter measured data indicate: adequate ventilation is provided, internal air quality as defined by the CO 2 and %RH measurements is acceptable, comfortable internal temperatures are achieved. The summer measured data indicate: acceptable ventilation is provided, comfortable internal temperatures are generally maintained though the lower design value temperature of 25 o C was sometimes exceeded the upper design value temperature of 28 o C was not. night ventilation does effectively reduce the effect of high external temperatures and with the aid of ground water cooling could prevent temperatures exceeding the lower limit temperature as well. BRE Energy Efficient Office of the Future (GB1) 11/11