pilot study report: school building waterland

IEA ECBCS Annex 35: HybVent

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INTERNATIONAL ENERGY AGENCY ENERGY CONSERVATION IN BUILDINGS AND COMMUNITY SYSTEMS

Pilot study report:

School building Waterland The Hague (Leidschenveen) the Netherlands

ing A. van der Aa, Cauberg-Huygen Consulting Engineers Rotterdam

[email protected]

This technical paper is not an official IEA-ECB&CS Annex 35 publication. The views and judgements expressed are those of the authors and do not necessarily reflect those of Annex 35 or IEA-ECB&CS.

I EA

Pilot study report: School building Waterland

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1 GENERAL INFORMATION 1.1.1 Report date: 01-02-02 1.1.2 Principal researchers

Cauberg-Huygen Consulting Engineers

1.1.3 Project title School building Waterland at The Hague (Leidschenveen) The Netherlands

1.1.4 Principal objectives Natural ventilation with support of mechanical ventilation, good IAQ, good thermal comfort, low energy consumption

1.1.5 Start date / End date: Design phase 1998-2000, Construction phase 2000-2001, Monitoring Phase 2001-2002

1.1.6 Number of man-hours The number of man-hours for the consulting of the building physics are about 200 hours. The number of hours for the consulting of the building services are about 500 hours

1.1.7 Project approach The project was started with a sensitivity analysis on ventilation, thermal comfort, daylighting and energy performance. Based on the results of the sensitivity analysis, hybrid ventilation gives several promising benefits on indoor air quality, thermal comfort and energy savings. The consultants designed the system on a level of performance specifications. Climate chamber measurements have been conducted on the performance of the system (capacity of components, thermal comfort, control system). After a tender, the contractors carried out the detailed engineering. The construction phase ended at the end of 2001. From then the monitoring phase has been started.

2 TEST SITE DESCRIPTION 2.1 Geographic information

2.1.1 Location: Longitude: 4.25°E, Latitude: 52.08 ° N

2.1.2 Elevation: 0 m above sea level

2.1.3 Terrain: Site plan, urban area, surrounded by mainly low rise buildings

2.1.4 Orientation: North-east and south-west

2.2 Climate information (Summary) Weather data on hourly basis are available from the Dutch Test reference year (TRY)

2.2.1 Location of meteorological station Meteorological station De Bilt. The meteorological data of De Bilt are rather similar to The Hague.


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2.2.2 % frequency wind speed versus wind direction Mean windspeed 3,5 m/s, main direction S/W

Mean wind speed per orientation

02468

1012

022,5

45

67,5

90

113

135

158180

203

225

248

270

293

315

338

2.2.3 Air temperature

Design temperature winter –7 °C

Monthly outdoor temperatures

02468

1012141618

Jan

Feb

Mrt

Apr

Mai

Jun

Jul

Aug

Sep Okt

Nov

Dec

Month

T ou

tdoo

r °C

2.2.4 Degree day information 3129 heating degree days (18°C baseline)

2.2.5 Daylight / solar radiation

Direct solar radiation on hor. surf.

0100200300400500600700800

2 4 6 8 10 12 14 16 18 20 22time [h]

Q d

ir [W

/m2] 21-jun

21-mrt21-dec


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2.2.6 Cloud factor

60 % clouded, 40% clear sky

2.2.7 Relative humidity & precipitation

Monthly humidity outdoors

0

20

40

60

80

100

Jan

Feb

Mrt

Apr

Mai

Jun

Jul

Aug

Sep

Okt

Nov

Dec

Month

Rel

ativ

e hu

mid

ity [%

]

2.2.8 Soil temperature Soil temperature 10 °C at 3 m below the surface. Soil structure clay and moor.

3 BUILDING DESCRIPTION 3.1 General description

3.1.1 Building name Scholencomplex Waterland

3.1.2 Building type School building

3.1.3 History New build building completed in autumn 2001

3.1.4 Design philosophy for IAQ and thermal comfort, energy efficiency and other issues of concern The design task was to develop a low energy concept (reduction of 15% compared to the Dutch building regulations) and to realise a good thermal comfort. The requirement of the property developer (municipality of Leidschendam, The Hague) was to apply natural ventilation, with support of mechanical ventilation. This made the application of hybrid ventilation in combination with openable windows a quite logical choice. To avoid cross ventilation, each classroom has been equipped with a local ventilation system, that consists of 2 electronically controlled inlet grills in the facade and a fan supported natural exhaust chimney. CO2 sensors and temperature sensors automatically control the ventilation system. To meet the energy performance requirements the building has a high level of thermal insulation (U-values of opaque parts 0,31 W/m2/K, U-value of windows 1.8 W/m2/K), good air tightness and energy efficient building services (high efficiency natural gas-boiler for heating and domestic hot water and high frequency lighting). An extra 30% energy savings above the mandatory level of the building regulations are provided by the hybrid ventilation system (15%) and daylight sensors and a central sweep switch on the lighting system (15%).


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3.2 Building geometry & materials 3.2.1 Plan view

3.2.2 Elevation

Elevation: 1-2 floors, 3-6 m building height.


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3.2.3 Building shape

A typical feature of the building is the twisted roof


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3.2.4 Volume Total volume for building (i.e. including structure) Approx. 17.000 m3

3.2.5 Floor area & materials 5,700 m2 floor area U-values of opaque parts 0.31 W/m2/K

3.2.6 Ceiling height 2.90 m U-values of opaque parts 0.31 W/m2/K

3.2.7 Façades (external walls) U-values of opaque parts 0.31 W/m2/K


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3.2.8 Windows U-value windows 1.8 W/m2/K, g-value = 0.60 No external shading

3.2.9 Number, volume and layout of rooms 52 classrooms of about 50 m2 each

3.2.10 Attic, basement, crawlspace No attic, no basement. Crawlspace present, not used.

3.2.11 Interior walls, including moveable partitions Internal separations of masonry and gypsum board

3.2.12 Interior doors and devices

3.3 Air leakage data Within the Energy performance calculation a maximum air leakage of qv;10= 0,193 dm3/sm2 floor area at a pressure difference of ∆P = 10 Pa is assumed. In accordance to the Dutch Building Regulations (Bouwbesluit) the maximum acceptable air leakage is qv;10 = 200 dm3/s per 3000 m3 building volume. Per classroom of 55 m2 floor area this equals qv;10 = 10 dm3/s (n50≈0.67) . Pressure test measurements have been carried out in two classrooms. The measurements result in a qv10 ≈ 32 dm3/s due to a major leakage at the construction of the air inlet grills in the facade. This defect has been repaired by the building contractor.


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3.4 Space heating The heating system consists of a T = 90-70 °C watersystem. The heating source is a high-efficiency gas boiler. Each classroom is heated by two convectors, located underneath the air inlet grills. Convector and inlet grill are located behind a covering panel

The convector is visible when the covering panel is removed. The inlet grill (not visible) is just above the convector.

3.5 Ventilation 3.5.1 Ventilation principle

The ventilation principle is stack- and wind-driven natural ventilation with fan assistance per classroom. The hybrid ventilation system consists of electronically controlled inlet grilles in the facade and an exhaust chimney at the roof. The exhaust is supported by a low-resistance fan, which is switched on when natural driving forces are insufficient. CO2 sensors measure the IAQ. Temperature sensors measure the internal temperature. A central control system (Lon-bus) controls the air inlets and fans, based on CO2 concentration and temperature measurements.


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3.5.2 Components

The following components are used to solve the main issues: • Air inlets electronically controlled inlet grills, equipped with a servo-motor; • Air exhaust (fan supported, natural exhaust chimney); • Control system; • Sensors (CO2 and temperature).

3.5.2.1 Fresh air inlets The air inlets consist of electronically controlled inlet grilles equipped with a servomotor. They are located below the windows and behind a convector in order to avoid draught problems.

3.5.2.2 Air exhaust

The exhaust consists of a chimney, containing a fan, which is designed for natural ventilation. Special attention has also been paid to the cowl pressure loss and the sound pressure level of the fan. Underneath the exhaust a tray is mounted for acoustical absorption and to prevent draught problems.


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3.5.2.3 Exhaust fan A low-pressure fan is used to avoid fan-induced pressure losses in the chimney.

3.5.2.4 Heat recovery No heat recovery is applied

3.5.2.5 Filtration No filtration, The air inlet grills have a grid to prevent insects to enter the classrooms.

3.5.2.6 Ducts No ducting has been applied

3.5.3 Frequency of operation, duration of operating cycle Based on the measured CO2-concentration in the classroom, the ventilation system is operated. Besides that during summer night time the ventilation system is switched on to cool down the building.

3.6 Internal loads 3.6.1 Pattern of occupancy

The classrooms are occupied during weekdays approximately from 8.30 till 16.00 hour with about 25 children and one teacher. In the weekends there is no occupancy.

3.6.2 Lighting A high-frequency lighting system of 8W/m2 is installed based on a level of 400 lux on the desks. The lighting system is manually switched on per classroom. The light-tubes at the facade zone are equipped with a daylight sensor, which adjusts the power of the light in dependence of the daylight level. A central sweep-switch system switches of the lighting system after occupied hours and during noon break.


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3.7 Control system and control strategy for ventilation and space conditioning

3.7.1 Type of system A central BEMS-system, based on Lon-bus technology, controls the ventilation devices.

3.7.2 Parameters monitored The control of the IAQ is based on measurement of CO2 per classroom The indoor and outdoor temperature per zone are measured to control the summer night cooling. A local temperature sensor connected to a thermostatic valve on the convector controls the indoor temperature per classroom. The artificial lighting system is also controlled and connected on the central control system. Based on the daylight levels the lighting devices in the window zone are controlled. Next to it all artificial lighting is centrally switched off during non-occupied hours.

3.7.3 Sensors In each classroom a CO2 sensor measures the IAQ and a local temperature sensor measures the indoor air temperature. On a central level, per zone, a temperature sensor measures the indoor and outdoor temperature. Per classroom a temperature sensor, connected to a thermostatic valves measures the indoor temperature.

3.7.4 Control strategy & internal design conditions The control strategy for the ventilation system is given in the table below. Control strategy during winter and summer

Winter: During day control on IAQ, local control per classroom: − If CO2 > 700 ppm: Inlet grill 1 is opened − If CO2 > 1000 ppm: Inlet grill 2 is opened − If CO2 > 1300 ppm: Fan is switched on During night inlet grills are closed (CO2 concentration < 650 ppm) Fully automatic User control of windows Frost protection by thermostat at inlet grill 1 Summer: During day control on IAQ, local control per classroom: − If CO2 > 700 ppm: Inlet grill 1 and 2 are opened − If CO2 > 1300 ppm: Fan is switched on During night central controlled night cooling as long as: − Tinternal ≥ Texternal + 2°C − Texternal > 15 °C − Tinternal > 20°C Fully automatic User control of windows


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3.8 Pollutant sources 3.8.1 Interior sources

No interior pollutant sources of importance

3.8.2 Exterior sources No external pollutant sources of importance

3.9 Costs Additional costs for the hybrid ventilation system are about € 100.000, compared to the standard budget for school buildings in the Netherlands. These additional cost are mainly caused due to: • Advanced Control system with Lon-bus and CO2 sensors • Daylight control of the artificial lighting system

3.10 Monitoring programme At the end of 2001 the monitoring programme has been started. The monitoring phase will last about 12 months. The monitoring programme consists of three parts: 1. Monitoring control strategy, fan operation hours, position of the inlet grills, CO2 concentration and air

temperature in two classrooms; 2. Monitoring of the energy consumption of the building (natural gas and electricity); 3. Momentary measurement of comfort parameters: temperature, RH, sound pressure level (fan), air

velocity. In two classrooms every 10 minutes the following data are monitored by the control system: • CO2 concentration; • Position of inlet grills; • Room temperature; • Outside air temperature; • Fan operation; • Lighting operation. Per day the data are collected in a file that is send to Cauberg-Huygen by e-mail.

3.11 Results from monitoring programme In the beginning of the monitoring phase in one classroom (reference case) only natural ventilation has been applied. The second classroom was equipped with a hybrid ventilation system. From February 2002 hybrid ventilation is applied in both classrooms.

In the figures below the results of a typical day in December 2001 are shown for a room with only (controlled) natural ventilation and for a room with hybrid ventilation.

Measurements 12-11- 01 reference

0,00

500,00

1000,00

1500,00

2000,00

2500,00

0:00 2:30 5:00 7:30 10:00 12:30 15:00 17:30 20:00 22:3010,0011,0012,0013,0014,0015,0016,0017,0018,0019,0020,0021,0022,0023,0024,0025,00

CO2_04TEMP_04KLEP1_04KLEP2_04VENT_04

Reference classroom


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Cumulative freq. curve for CO2 levels, Feb. 2002.

0

500

1000

1500

2000

0 20 40 60 80 100Cumulative frequency distribution (%)

CO

2 con

cent

ratio

n (p

pm)

Running hours of fan

0

10

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30

40

50

60

70

80

0 5 10 15

Windspeed (m/s)

Run

ning

tim

e du

ring

occu

pied

ho

urs

(%)

Room 4

Hybrid ventilated classroom The maximum CO2 concentration in the reference room with natural ventilation inlets accounts nearly 2000 ppm. The automatic control of the inlet grilles takes care of a fresh air supply at raising CO2-levels, but is not sufficient to keep the concentration below 1500 ppm. The hybrid-ventilated room does not exceed a CO2-level of 1500 ppm, due to the operation of the fan. The fan is switched on at a CO2-level of 1300 ppm and a significantly better indoor air quality is reached. Due to some starting-up problems of the BEMS-system and problems with the CO2-sensors no suitable data are available from the first weeks of 2002. The occurring CO2-levels in February 2002 during the occupied hours are worked out in the figure given alongside. The classrooms are occupied during 9 hours per day. The figure shows that 95% of the time the CO2-level is below 1500 ppm. The average level is approx. 1200 ppm. Based on the switching points of the grills (700 and 1000 ppm) and the fan (1300 ppm) it can be deduced that 86% of the time one inlet grill is opened, 65% of the time both grills are opened and 25% of the time the fan is switched on. These values are quite in range with the design values. The outdoor climate data windspeed, wind direction temperature have been derived from the TNO weather station in Delft, that is located within 10 km from the Waterland school building. The figure alongside shows the relationship between the relative number of fan operation hours per day and the 4-hour average wind speed for February 2002. As expected the operation hours of the fan decrease when the average wind speed increases.

Measurements 12-11-01 hybrid ventilation

0.00

500.00

1000.00

1500.00

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2500.00

0:00 2:30 5:00 7:30 10:00 12:30 15:00 17:30 20:00 22:3010.0011.0012.0013.0014.0015.0016.0017.0018.0019.0020.0021.0022.0023.0024.0025.00

CO2_03TEMP_03KLEP1_03KLEP2_03VENT_03


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1.0

10.0

100.0

1000.0

1.0 10.0 100.0drukverschil [Pa] --->

Qv

[dm

3/s]

--->

meetpunten regressie-analyse

3.11.1 Air tightness and capacity of inlets In October 2001 pressurisation tests have been carried out to control the air tightness of the building and the capacity of the inlets. The measurements were conducted in the two monitoring rooms. The air tightness of buildings in The Netherlands is expressed as an qv;10-value, which is defined as the airflow at a pressure difference of 10 Pa. The energy performance calculations assume a qv;10 of 200 dm3/s per 3000 m3 building volume, which results in a qv;10 of 12 dm3/s per classroom. The measured qv;10-value for room 1 is 31,1 dm3/s and for room 2 is 33,9 dm3/s. Further inspections showed that a joint around the inlet grills was not sealed. The building contractor has mended these defectives. The capacity of the inlet grills has also been measured by pressurisation tests. The design is based on a capacity of 530 m3/h at a pressure difference of 3 Pa. This in contradiction with the Dutch building regulations where a capacity is defined and required at a pressure difference of 1 Pa. The figure gives the measurement results. The measured capacity is 368 m3/h and is 30 % lower than the design value. This is caused by the deviating construction of the air inlet compared to the design details. This means that the design flow rate will be reached at a pressure difference of 6 Pa. If the pressure differences of the natural driving forces are below this threshold the fan will be switched on more frequently.

3.11.2 Thermal comfort At the beginning of February u number of occupants complained about draught problems from the air inlets. Therefor measurements were carried out on inlet temperature and the air velocity near the inlets. The air inlets are located underneath the windows and behind a convector. The figures below give an impression of the air inlets.

Measurements were conducted on the temperatures and air velocity around the inlets. In the figures below the results of the temperature measurements are given. Figure a gives the temperature of the incoming air. Figure b shows the outdoor temperature and figure c shows the temperature difference between the water supply and water return of the convector.


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Fig.a. Temperature of inlet air Fig b. Outdoor temperature Fig c.Water temperature difference convector The indoor room temperatures during the measurements are between 20-25 °C. The measured air velocities from the air inlet are given in the table below.

Measured air velocities at air inlet 46 cm above floor.

Wind

speed(m/s)

Wind

direction

Air speed:

x=0 m

x=0,3 m

x=0,6 m

x=0,9 m

x=1,2 m

x=1,5 m

1-03-02 3,5 NW 0,44 m/s 0,33 m/s

0,17 m/s

<0,1 m/s

<0,1 m/s

<0,1 m/s

6-03-02 6,5 WZW >1

m/s

>1

m/s

>1

m/s

0,75 m/s

0,71 m/s

0,55 m/s

Based on the measurement results it is clear that the complaints of the occupants are correct. Further research on location with smoke tests showed that at low wind speeds no sufficient mixing of air appeared. At higher windspeeds the cold air is pushed through the convector in the wrong direction and leads to incoming cold air at floor level.

0.0

5.0

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15.0

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25.0

30.0

0 24 48 72 96 120Tijd (uur)

T (C

)

deltaT

T_OUT

-5.00.05.0

10.015.020.025.030.0

T(C

)

T_OUT

-5.0

0.0

5.0

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25.0

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0 24 48 72 96 120

Tijd (uur)

T (C

)

T_lucht


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To improve the situation some modifications at the convector have been applied. The figure below shows a cross section of the inlet before and after modification. A kind of labyrinth was created around the convector. This forces the incoming air to flow through the convector.

Alongside a photo of the modified air inlet is given. The results of the temperature measurements after modification are given in the figures below. The indoor room temperatures during the measurements are between 20-25 °C. The measurements after modification show a significant improvement of the inlet air temperature to at minimum 20 °C during occupation hours. The water temperature difference of the convector is 15-20 °C at heat demand, which shows that the heat exchange of the convector is significantly increased. The inlet air at occupied hours has increased to 23 °C.

Cross section of convector before and after modification


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The labyrinth construction increases the airflow resistance of the inlets. Therefore the air velocity reduced with about 30%. To avoid complaints about the velocity of the horizontal air flow from the inlets a modification has been proposed to create a vertical inlet. During the measurements the position of the sensor of the thermostatic valve has been replace above the convector. This has been done to switch on the convector in dependence of the inlet air temperature. In practice this means that the thermostat no longer controls the indoor air temperature, but only the inlet air temperature. Therefore a modification has been proposed to create an adjustable bypass over the thermostatic valve, which allows a small water flow over the convector to preheat the incoming air. The temperature of the supply water will be tuned in accordance to the required heating temperature of the inlet air, and the outdoor temperature

3.12 Lessons Learned The hybrid ventilation system at the pilot project Waterland is one of the projects which has been developed, engineered and constructed during the running phase of the IEA Annex 35 program. Since September 2001 the building is in use. Due to this fact information is available from the very first stage of the project until the operation phase. For lessons learned comments are given per stage. Preliminary Design stage The principal idea of the project was to get a natural ventilated building, supported with mechanical ventilation. Next to it an energy performance was required which was 15% lower than the minimum level according to the Dutch building regulations. However no clear description was given about the thoughts lying behind this idea. The occupants of the building (school director, teacher’s etc.) were not consulted in the design plan, which led to a number of discussions in latter phases of the design.

T_OUT

-5.00.05.0

10.015.020.025.030.0

T(C

)

T_OUT

-5.0

0.05.0

10.015.0

20.025.0

30.0

0 24 48 72 96 120 144 168

Tijd (uur)

T (C)

T_lucht

deltaT(C) na

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25.0

30.0

0 24 48 72 96 120 144 168

Tijd (uur)

T (C)

deltaT

Fig a. Temperature of inlet air

Fig b. Outdoor temperature

Fig c.Water temperature difference convector


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No clear performance specifications were given about the targets to be reached. A 15% lower energy performance in combination with an advanced ventilation system is much more expensive than a standard school building. Only a minor extra budget was disposed. Design stage In the beginning of the design stage the rough ideas of the principals evolved to a fully hybrid ventilation system. This had the support of the architect, however the lack of good examples made the discussions more difficult. Particularly the discussions with the users took some time. The main point was to convince non-technical people about the benefits of a hybrid ventilation system. Barriers encountered were: • Fear of less IAQ and thermal comfort • Fear of less reliability of the system • Fear of “Big Brother” system – everything is controlled, without the possibility of individual control • No conviction about the extra quality of a hybrid ventilation system • No willingness to pay extra for hybrid ventilation The design team of the building consisted of an architect, a construction consultant, a building physics consultant and a consultant for the building services. The building physics consultant developed the concept of the hybrid ventilation system. The consultant of the building services did the engineering. A problem was that this participant only had a contract for delivering a performance design and not a complete design. This led to a tender document in which quite a number of components were not specified, but only described in terms of performance specifications. Barriers encountered at the design team were: • Fear of increase of the design fee for the designers • Fear of not succeeding • Fear of increasing overall investment costs • Uncertainties due to lack of information • Uncertainties due to lack of suitable design tools • Fear of the aesthetic impact of chimneys • Fear of complaints afterwards from the occupants and claims Tender stage After the design a tender was held among several contractors. The tender was separated in a building part and a building services part. The result of the tender was a substantial overrunning of the budget. After laborious negotiations with the potential contractors major changes were made in the design. The mainly wooden design was changed into a concrete construction in combination with masonry. The hybrid ventilation system was altered from a design with natural/mechanical supply and natural exhaust into a system with natural supply and natural/mechanical exhaust. These decisions were taken based on cost reduction, without a thorough redesign. Barriers found by the contractors were: • Fear of increase of construction costs • Fear of uncertainty of the performance of the systems and, due to that claims, afterwards • Unwillingness of innovation Construction stage Due to the performance based contracts with the contractors, a number of things of the hybrid ventilation system had to be designed by the contractors. These parties are not the right ones to develop a new sophisticated ventilation system. The design team which officially had a control function in this phase did however quite a lot of the design work. The construction of the building in this phase went rather fast, little time was left to design and engineer a new hybrid ventilation system. This led to several compromises.


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Labtests of the natural/mechanical exhaust showed that the combination of the natural exhaust chimney and a low-pressure axial fan was very sensitive. A combination had to be found which had the following performances: • Sufficient natural flow in the natural mode. The first selected fan had a too big air resistance in the

stand still mode • A low noise level in the mechanical mode • Sufficient flow in the mechanical mode • In a very late stage of the construction phase the decision was taken to change the cowls of the exhaust

chimneys in one with a lower resistance. Operation stage The performance of the hybrid ventilation system of the Waterland school building has been monitored since December 2001. The indoor air quality, the indoor temperature are measured by the central BEMS-system. Besides that the energy consumption is measured for the whole building per zone and specific for both classrooms. So far, no information is available about the energy consumption. The measurements show that the indoor air quality is good. During 95% of the time the CO2-concentration is below 1500 ppm. The ventilation devices are controlled, based on the CO2-concentration in the classrooms. The fan is switched on during 25% of the occupied hours, which is in line with the design expectations. The measurements also reveal thermal comfort complaints. The preheating of inlet air is not sufficient and the air velocity near the inlets is too high. Therefor some adjustments have been tested to improve the situation. A labyrinth construction has been made at the air inlets, a vertical air inlet will be created and a bypass over the thermostatic valve is proposed. During the year 2002 the monitoring will be continued.

pilot study report: school building waterland

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