THE GRONG SCHOOL...2

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1 1 Content 1 THE GRONG SCHOOL DESCRIPTION OF THE PROJECT School and Community House Plan principle...3 THE ENERGY SAVING CONCEPT AND THE TECHNOLOGIES Solar heating Daylighting Ventilation ENERGY SAVINGS AND REDUCED EMISSIONS Recorded energy supply CO 2 emissions...9 EVALUATION OF INDOOR ENVIRONMENT Air quality and thermal comfort Daylight conditions COSTS CONCLUSIONS AND LESSONS LEARNED Ventilation Daylighting...12 KEY PROJECT DATA REFERENCES...13

2 2 1 The Grong School Author: Karin Buvik. SINTEF Dep. of Architecture and Building Technology. N-7465 Trondheim, Norway. NORWAY Fig. 4.1 Photo from September Description of the project The energy conservation and solar strategies in the Norwegian MEDUCA project was: Use of solar energy for space heating and pre-heating of ventilation air. Use of daylight to reduce the consumption of electric energy for artificial lighting. Separately operating zones for artificial lighting, and control by daylight sensors contribute to energy efficiency. Use of natural driving forces for ventilation, buoyancy and wind, result in a minimum of fan power. Further, airflow controlled by CO 2 sensors, heat recovery, and low-emitting building materials contribute to energy efficiency. The new wing is a one-story school building. Classrooms are situated on the northern side of a central circulation spine. Common rooms, rooms for group activities, storage rooms, and locker rooms are located on the south side. On the top of the building, in the attic, there is a solar collector (sunspace), which gives light to the classrooms, heat to the exhaust air and thereby extra driving forces for the ventilation air, plus heat to the intake air via the heat recovery system. North facing classrooms have no need for glare reduction devices or shading systems, but have low heat gains and thus increased need for heating during winter. To increase solar gains the exhaust air chamber (top of the building) is designed as a solar collector (sun space), which gives heat to the fresh air via the heat recovery in the exhaust tower, and also gives some sunlight into the classrooms. The internal walls of the sunspace are glazed in order to allow daylight to reach the back of the classrooms. The roof monitor (sunspace) design optimises passive solar heating and even distribution of daylight on the workplaces. The new building was completed in August 1998.

3 School and Community House The building complex is going to be renewed and extended. A task was to find suitable solutions for co-ordinated use between the school and the community house. Many rooms are planned for social and cultural activities, as well as for teaching and learning. 1 main entrance 2 vestibule 3 exhibition 4 wardrobe 5 café 6 homemaking 7 amphitheatre 8 library 9 administration years old years old years old 13 swimming pool 14 gym/assembly hall 15 hall Fig After renovation. Project Plan principle Homebases for the primary and lower secondary school contains classrooms, activity rooms, rooms for small groups and entrances. An objective was to create a flexible area, which may be divided into landscapes. Rooms for gatherings are obtained by the possibility of opening up between classrooms and activity rooms. North 1 entrances 2 wardrobes 3 activity rooms 4 groups 5 training (ADL) 6 classes. Fig Plan of the new wing

4 4 1.2 The energy saving concept and the technologies Fig South fasade. Primary and lower secondary school to the right Fig North fasade. Primary and lower secondary school to the left Solar heating A sunspace runs along the entire ridge of the building. The tilted south facing glazing was designed to optimise the use of incident solar energy over the year. The sunspace also functions as a roof monitor that transmits daylight into the classrooms; and it serves as a ventilation air exhaust chamber as well. The sunspace (solar air collector) is expected to allow for a high fraction of usable solar heat contribution. Heat loss to ventilation air represents a large portion of the heating energy requirement in cold climates. A system of indirect ventilation air pre-heating is employed. Solar radiation incident on the south facing glass of the sunspace will cause the temperature of the exhaust air to rise. The heat is recovered at the exhaust tower and exchanged to the fresh air at the underground air intake tunnel Daylighting The internal walls of the sunspace are glazed in order to allow daylight to reach the back of the classrooms. Three different methods were used to simulate the daylight levels in the classrooms. The selected roof monitor (sunspace) design optimises passive solar heating and even distribution of daylight on the workplaces. Model studies A model of a typical section of the building is analysed, using an artificial sky. The classrooms are located on the northern side of a central circulation spine. Rooms for group activities, storage rooms, restrooms, and locker rooms are located on the south side. North facing classrooms have no need for glare reduction devices or shading systems, but have low heat gains and increased heat losses during winter.

5 5 base case SP1 SP2 SP3 SP4 SP1 SP2 SP3 SP4 alternative 1 Alternative Daylighting Designs Daylighting analysis was integrated with passive solar heating analysis, using an analysis model based on monthly average temperature and global radiation data. Three alternative designs were compared. First the impact on the annual combined lighting and auxiliary heating energy demand of alternative daylighting designs was investigated. In order to do a cost-benefit analysis, it was necessary to analyse the utilisation of daylight for the illumination of interior spaces. An analysis of passive solar heating to reduce the auxiliary heating energy demand was also required. Finally, an analysis of clear-day room temperatures was performed in order to produce indicators of the thermal comfort levels of the alternative designs as compared to the base case. Based on the findings from the analysis, alternative 2 was incorporated into the final design. SP1 SP2 SP3 SP4 alternative 2 Different design alternatives showing view of the sky from four station points. North is to the right. Artificial Lighting Controls Separately operating zones of artificial lighting is implemented in order to reduce uneven lighting levels and contribute to energy savings. Timers and daylight sensors are used to control the artificial lighting Ventilation An air inlet tower is located outside the building. The air is brought into the building through an underground tunnel that connects the air intake tower to a distribution chamber below the central circulation spine. Exhaust air is extracted through the exhaust chamber (sunspace) above the circulation spine. A centrally located exhaust tower at the top of the building provides the necessary stack effect. Fig Section of the new wing The underground supply air duct provides for pre-heating of ventilation air in the winter season through ground coupling; and precooling of the air during the summer. Increased nighttime ventilation

6 6 during overheated periods provides a significant amount of cooling energy to the building with an estimated 12-hour time lag. The supply air, which is distributed in the classrooms by displacement ventilation, is introduced at floor level through low-velocity diffusers. Warm and contaminated air rises and leaves the room at ceiling level, through controllable dampers, into the exhaust chamber. Sunspaces in the attic The following modes have been identified: Winter day - regular school day: Air preheated in underground duct, by heat recovery and by hydronic coil. Perimeter heaters on when needed. Room exhaust dampers controlled by CO2-level Winter night - school closed: Perimeter heaters on when temperature gets below 15 C Mid-season day: Same as winter day Mid-season night: Same as winter night Summer day: Exhaust fan starts and exhaust dampers open in situations of unsatisfactory indoor air quality or temperature level above set point. Exhaust air is led around exhaust air heat exchanger. Summer night: Night ventilation through underground supply air duct in order to chill it s thermal mass, which will provide precooling for the supply air on the following day; high airflow rate when high temperatures are expected. Wardrobes and toilets are provided with overflow air, and the exhaust air is being mechanically extracted from the toilets. In order to reduce air contamination by source, low-emitting materials has been used predominantly. Lower emissions from materials allows for a substantial reduction of the air change rate, which in turn promises a decrease in the heat loss to ventilation air during the heating season. The sunspace/exhaust air chamber was designed to assist the movement of air. The driving force represented by the hot air in the exhaust chamber reduces the need for fan assistance. This is particularly important in summer season when increased ventilation air volume is used to cool the building. Fan Assisted Supply and Extract Fans are installed both at the supply side and the exhaust side. The supply fan is supposed to ensure a steady air flow into the building, while the exhaust fan is used to achieve forced ventilation for cooling during summer when buoyancy forces are insufficient. A preliminary study indicated that wind-driven natural ventilation could not provide satisfactory ventilation at all times. Calm periods of 5-7 days have been reported at the site. Buoyancy-driven ventilation is considered reliable for the coldest part of the heating season, but it may not work sufficiently for summer conditions and for some periods during spring and fall. Additionally, the installed filters and heat exchangers cause an airflow pressure drop. Hence, fan-assisted buoyancy driven ventilation strategy was employed in the final design. Heating and Cooling To day the school has an electric and oil fuelled hot water heating. Connection to a planned biomass fuelled district heating system is intended. Pre-heating of supply air during the winter occurs in three steps: First by the thermal mass in the underground supply air duct, then by a heat exchanger providing heat from the heat recovery system, and finally by a hydronic coil heat exchanger.

7 7 The building itself is considered as light, but brick walls between the classrooms and the circulation space, and the concrete floors, provide some thermal mass. The solar gains from the sunspace will also add heat to the heat recovery system during spring and fall. On cold days, a net heat loss from the exhaust airflow through the glazed areas will contribute to an expected decrease in the stack effect by less than 10 %. Since the temperature of the basement distribution chamber is set at 19 C, it can be claimed that the central corridor of the building has a kind of passive radiant floor heating system. The underground supply air duct will also provide a considerable precooling of the air during the summer. However, with a design summer temperature of 23 C, the cooling demand is relatively low. Pre-cooled ventilation air may still be called for, particularly in early fall when low sun angles and predominantly clear skies could occasionally Placing the exhaust tower The exhaust tower was constructed in a workshop and tested to secure a low pressure-drop in the airflow through heat recovery and damps. The tower was transported to Grong and placed on the school building. Patented dampers A wind resistant exhaust damper has been designed by ROOMVENT DESIGN dr.ing. Per O. Tjelflaat. The exhaust damper uses a windshield combined with self-adjusting vanes and a Venturi geometry. The design has been patented. The wind resistant exhaust damper is available through: Auranor AS, P.O. Box 100, N 2712 Brandbu, Norway d/auranor.html Heat Recovery Heat is recovered from the exhaust air in the exhaust tower by the use of a heat exchanger. The recovered energy is then used to heat the supply air via another heat exchanger placed between the underground supply air duct and the distribution chamber. A water-glycol loop conveys the heat between the heat exchangers. The expected heat recovery rate is some %. Expected pressure losses are 25 Pa for the inlet air exchanger and 28 Pa for the exhaust air exchanger. A considerable pre-heating of the air will also occur in the underground supply air duct, before the heat recovered from the exhaust air is added. During periods when heat recovery is not needed, the exhaust air bypasses the heat exchanger in order to avoid creating a pressure drop. Filters and Fans A mosquito net is installed in the air intake tower. Fine filter is installed at the end of the underground air inlet duct, just before the inlet heat exchanger unit. The pressure loss through it is substantial, about 20 Pa for a new filter. It is assumed that large particles will be deposited in the underground supply air duct, before reaching the fine filter. Fans are of the propeller type, having a diameter close to the inner diameter of the duct. The supply fan, which is placed in the air inlet tower, has the ability to enhance the pressure by some 70 Pa. The exhaust fan, which is placed at the lower end of the exhaust tower, will add a pressure of about 35 Pa to the system.

8 8 Controls CO 2 sensors control the airflow through the exhaust valves mounted in the glass wall between the classrooms and the sunspace. Temperature sensors for control of the heating system are installed. Perimeter radiant heaters are engaged during cold periods to prevent the temperature to drop below 15 C. 1.3 Energy savings and reduced emissions Energy Building performance - Calculated values Electrical Energy Savings Compared to a Conventional Building Avoided use of high grade electrical energy due to daylight responsive controls of artificial lighting: 10.2 kwh/m 2 -year. Avoided use of electricity for ventilation fans due to natural ventilation: 9.2 kwh/m 2 -year. SUM: Reduced use of electricity: app. 20 kwh/ m 2 -year. Thermal Energy Savings Compared to a Conventional Building Reduced auxiliary heating energy demand due to the incorporation of a sunspace roof monitor: 6.9 kwh/ m 2 -year. Reduced demand for heating energy due to low energy windows, low emitting materials, and demand controlled, hybrid ventilation: 8.7 kwh/ m 2 -year. SUM: Reduced demand for heating energy: app. 16 kwh/ m 2 -year Recorded energy supply Recording Period: 1 st August th November 2000 (close to 27 months) Electric energy consumption: 46,458 kwh Delivered energy as hot water from neighbour building: 175,302 kwh The average annual energy use Electric: 46,458. (12/27) = 20,648 kwh Oil: 175,302. (12/27)/0.9 = 86,669 kwh An oil-fired boiler produces the hot water, and the efficiency is taken as 0.9. The specific energy use The gross useful area in the school building is 1001 m 2. The heated culvert area and the exhaust duct (sunspace) area are 160 m 2 each, but are not considered useful for occupants. Electric: 20,648/1001 = 20.6 kwh/(m 2. year) Oil: 86,669/1001 = 86.5 kwh/(m 2. year) Comments to the energy consumption Electrical energy consumption is 20,648 kwh over a year. The predicted value is 12,400 kwh. Lighting is assumed to make the major part (80%). More hours of occupancy than assumed in the prediction may be a cause for the higher consumption. The BEMS make the fans run without any need for ventilation as explained below. The yearly consumption of hot water for heating is 86, = 78,002 kwh. The predicted value is 55,800 kwh. The reason for the higher consumption can probably be found in: The faulty CO 2 -sensor in room 125 makes the BEMS believe that there is a high level of CO 2 in the room, and the system run the fans at full speed to supply more fresh air to the room. This process goes on even at night, and demands more energy to heat the supply air. The prediction has been carried out for a simplified scenario. Not accounted for are: infiltration (rather exfiltration) above 0.01 ach., thermal bridges in the envelope, heat loss from air exhausted from

9 9 the restrooms and directly to outside, and heat loss from the heated part of the ventilation culvert. Actual hours and intensity for use of the building may be different to what is assumed. The heat gain and the heat loss from the glazed areas on the roof (sunspace) have been accounted for in a way that is not expected to give very accurate results. Several minor faults with the building itself and with the ventilation system, leading to discomfort for occupants and excessive energy consumption, were corrected in 1998/99. * Progress report The long-term measurement logging of data from outdoor and indoor climate and from HVAC system parameters was delayed due to problems with BEMS. New software for the BEMS has been funded by NVE, and was installed in December Long-term monitoring started in January A recent review of data, collected for the period 7 March till 10 April, shows that the demand-controlled ventilation has worked very well. The energy consumption for the first 3 months of 2002 has been reduced, compared to Total consumption for the period in 2001 was 84,600 kwh while it is 65,600 in The reduction is found in the consumption of hydronic heating; a reduction from 74,400 kwh to 54,000 kwh, i.e. 27 % reduction. There seems to be a reduction in degree-days (Trondheim) of about 14 % this year compared to last year (degree-days for January and February only available at this time) that counts for a good share of the reduction in consumption. The rest of the reduction is probably due to the good functioning of the demand-controlled ventilation since December CO2 emissions The electrical energy is provided by hydro power, which has no CO2 emissions. The thermal energy is today provided by oil, but the oil will in the future be replaced by biomass, which is CO2 neutral. The yearly consumption of oil corresponds to a volume of: 86, /41.8/920 = 8.1 m Evaluation of indoor environment The leakage of the building envelope has been measured by using the supply fan of the building. The building is considered fairly airtight compared to requirements for similar buildings. Air leakage data: 0.83 ACH@50 Pa. Estimated after test at 10 Pa overpressure in building at T=20 C inside and outside, and no wind.

10 10 The ventilation system is very easy to inspect and to clean, and a long life can be expected for the system. No shoes that are used outside the building are allowed in the classrooms Air quality and thermal comfort The building, including the ventilation system, is capable of giving users acceptable air quality and thermal comfort in the heating season. For the summer season (cooling season), measurements have not been taken yet. However, no complaints were registered for the years 1999 and Test temperature measurement show that the intake air culvert has a cooling effect. The reading of some of the CO 2 meters in the building has been compared to the reading of a very accurate analyser. The meters in the building show generally higher values than the analyser does. Some values are more than 150 PPM higher. A difference within 50 PPM was expected. The southern wall with the clerestory windows. The picture shows ventilation supply and extract devices. It has been observed that use of asthma medicine among the pupils has diminished when the new school was taken into service Daylight conditions The building has secondary windows on the opposite wall to the window wall. The secondary windows are designed as a horizontal strip, situated just beneath the roof. They have lower transmission factor than the main windows, such that they do not dominate the room during overcast sky conditions. On sunny days they enable sunshine to enter the classroom, a very nice effect during wintertime. If sunlight penetrates the room too much, it can be diffused using the vertical louvers. The lager part of the solar radiation is then utilised for preheating the ventilation air. The distribution of daylight in the classrooms under the conditions of overcast sky is very even. A large southern part of the room has a high daylight factor of about 3 %. In the areas near the north-facing windows the daylight factor is between 8 and 9 %. The users are very happy with the daylighting conditions in the classrooms. The teachers who work in those classrooms evaluated daylighting in the classrooms as very bright and very even. They did not notice any veiling reflexes or shadows that could disturb the visual environment in the classrooms. Solar glare was experienced only in one classroom, where the mechanism for adjusting the louvers did not function properly. The colours were evaluated as rather natural and the colour temperature as neutral.

11 11 In spite of the fact that the sunshading used in the Grong school is very easy to use, it happens that it covers the south-facing windows unnecessarily in periods when the sun disappears but nobody changes the position of louvers or moves them to the side. Therefore, the daylight factor measurements were made a second time with vertical louvers covering the windows and adjusted to reflect sunlight back to the duct at the middle of the day. The results show that the daylight level is lower than for clear windows, but the mean daylight level is still higher than the level recommended by the Norwegians building code. As can be expected, the louvers shade mostly the southern part of the classroom. 1.5 Costs The total building costs are close to the average, normal costs. Building: NOK in 1998, i.e. ~ EURO. Floor area: m 2 Computer simulation Simulated daylight levels for the classrooms were calculated using the SUPERLIGHT computer program developed by the Lawrence Berkeley National Laboratory. The calculated values came close to the measurements of daylight factors derived from actual measurements of illuminance levels in a model, which was placed under an artificial sky. HVAC system including BEMS, concrete culverts and intake- and exhaust tower: NOK, i.e. ~ EURO. Conventional ventilation ductwork has been avoided. That may not only reduce the pollution level in supply air to rooms, but it may also reduce cleaning costs. The low velocities in airflow paths and in components such as air filter and heat exchangers, results in high component costs compared to conventional ventilation systems. On the other side, fan costs are lower due to less power demand for assisted natural ventilation. A very low consumption of electrical energy for the fans is achieved. Low fan power does result in low noise production that is another important benefit compared to conventional systems. Long underground ducts may be an extra cost, but used in an area with no infiltration of moisture and radon, it will be a great advantage on hot summer days. In addition, it seems like such ducts will reduce the power installation needed for supply air heating. The duct is also used for distribution of water end electricity. 1.6 Conclusions and lessons learned Ventilation A ventilation system design has been developed that works at times when stack-effect is insufficient. The largest problem for naturally ventilated buildings seems to be heat recovery from exhaust air along with low pressure-drop in the airflow. The heat-recovery units chosen for this building is a compromise between installation cost and pressure-drop. The units could have been reconsidered to allow for smaller pressure-drop, for example by

12 12 using convectors located in the end of the underground intake duct that is closer to the building. Need for research and development There is clearly a need for design guidelines for natural ventilation design in Nordic countries. Case studies should be presented, and recommendations should be given along with such guidelines. All components in the airflow path should be dealt with; also the design of underground air intake ducts and exhaust towers. In addition, there is a need for air handling equipment. Some of the existing ventilation system components should be tested for low pressure drop in order to learn their characteristics for design. There is also a need for developing components especially for natural or hybrid ventilation. Typically, there is a need for fans for installation in intake ducts and in exhaust towers to assist natural ventilation. As there is no demand for very compact heat exchangers in natural ventilation systems, new heat exchangers with the focus on low pressure drop and low cost should be developed. Demand controlled ventilation is even more needed in natural ventilation systems than in conventional ventilation systems as heat recovery from exhaust air is less efficient. Especially, correct placement of sensors in rooms is crucial to achieve effective and efficient climatization Daylighting There is a balanced usage of daylighting apertures in the classrooms, which allow daylight to penetrate into the rooms from to sides. The northern windows, which give a cool, bluish skylight, are clearly the primary daylight sources. The daylight level in the window zone is also highest. The clerestory windows have a secondary function. Since they are placed very high in the southern wall, they distribute daylight evenly over a large part of the room, without compete with the main windows. In spite of the fact that the sunshading used in the Grong school is very easy to use, it happens that it covers the clerestory windows unnecessarily in the periods when the sun disappears but nobody changes the position of louvers or moves them to the side. A better solution for the sunshading problem could be horizontal blinds. During sun hours, the unwelcome sunlight could be reflected

13 13 to the ceiling. During overcast sky hours, the horizontal blinds covering the windows would enable the skylight to penetrate the room much more than the vertical louvers do. As a result, the daylight level in the southern part of the room could be higher. Contact persons Karin Buvik, Project leader R&D SINTEF, Dep. of Architecture and Building Technology Karin.J.Buvik@sintef.no Per Olaf Tjelflaat Professor HVAC, NTNU per.o.tjelflaat@kkt.ntnu.no Kåre Herstad Letnes Architects kaare@letnesark.no Torbjørn Landsem HVAC consultant Fax: Key project data Location: Mediå, the centre of Grong municipality, in the middle of Norway, about 65 degrees north Site and surroundings: Semi-urban with low-rise buildings. Flat Owner: Research project: Architect: HVAC engineer: Electrical engineer: Structural engineer: Contractor: Construction work: The municipality of Grong SINTEF and NTNU, Trondheim Letnes Arkitektkontor A/S, Verdal PlanConsult VVS, Namsos Ryjord AS Nord, Steinkjer Planstyring AS, Steinkjer Cost Total building: 14,0 million NOK Cost HVAC: 1,5 million NOK Tor Nykvist & Søn AS, Namsos Started in September Completed in August 1998 Gross floor area: 1001 m 2 Number of storeys: 1, plus distribution ducts in basement and attic Floor to ceiling height: m (sloped roof) Personnel load: Outdoor climate: Heating: Heat recovery: 200 pupils + teachers and staff Summer design temperature: 23 C. Winter design temperature -23 C Unsteady wind speed and directions, relatively long calm periods. Periods with dust and pollen from agriculture. Particles from oil and wood burning during winter. Hot water convectors. Hydronic coil ventilation air pre-heating Glycol run-around system that pre-heats ventilation air 1.8 References Lerum, Vidar, Matusiak, Barbara, and Thyholt, Marit.

14 14 Daylighting Design for Grong Primary School. The SINTEF Group, STF22 A98509 Tjelflaat, Per Olaf, and Rødahl, Eystein. Design of Fan-Assisted Natural Ventilation. General Guidelines and Suggested Design for Energy-Efficient Climatization-System for Grong Primary School. The SINTEF Group, STF22 A97557