Category Archives: EuroSun2008-4

System efficiency, primary energy and CO2 emission

A major impact on the energy consumption and CO2 emissions is related to the efficiency of the heating and/or cooling system, its efficiency on production, emission, control and distribution. Conventional systems used in Passivhaus buildings must have a high performance level, should have low levels of emissions and primary energy consumption.

The energy consumption of a building can be expressed in terms of equivalent consumption in primary energy — Tons of Oil Equivalent — or in terms of CO2 emissions. However, the conversion factors are country dependent on the energy mix and the way the energy is generated. Renewable energy is favourably a good choice.

3.7 Appliances and lighting

The adoption of high-efficiency appliances can significantly reduce the total energy consumption. Whenever possible the design should rely on daylight and minimize the use of artificial light. Although inefficient appliances can help reduce heating loads in winter, this is a very inefficient way to heat a house. Also, internal gains from inefficient appliances increase summer cooling loads and the overall net energy balance is usually negative.

There are simple and effective passive strategies that minimize or reduce the energy consumed. Adopting them depends mainly on the occupants’ behaviour. Using the washing machines during night when the energy demand is reduced and cheaper, drying the linen in the sun instead of in a tumble dryer, switching off appliances instead of relying on standby mode are just a few examples.

Study of Different Curtainwall Facade Options

1.4. South-Facing Curtainwall Facade Scenarios

The impact of the five different south-facing curtainwall facade scenarios described in Table 2 on a building heating and cooling load was studied for the three cities identified in Table 1. For each scenario, the curtainwall was assumed to consist of 50% of a multi-layer glazing system as a vision section, and 50% of either spandrel panels or multi-glazing BIPV assemblies as the non-vision section. All the multi-layer glazing systems (with and without PV) were assumed to have low-e coating, 6mm glass panes, 20mm air cavities and aluminium framing with 19mm thermal break and insulating edge spacers. The vision sections characteristics were obtained with FRAMETMplus [13] using the curtainwall framing system. The U-value and SHGC were evaluated at 2.03W/m2oC and 0.39 for the double-glazed system, and 1.2 W/m2oC and 0.28 for the triple-glazed system.

Table 2. South-facing curtainwall facade scenarios.

#

Vision Section (50%)

Non-Vision Section (50%)

1

Double-glazed

Spandrel (U-value=0.55 W/m2oC)

2

Double-glazed

BIPV configuration A

3

Triple-glazed

BIPV configuration B

4

Triple-glazed

BIPV configuration C

5

Triple-glazed

Spandrel (U-value=0.55 W/m2oC)

Monitoring results

1.2 PV facade system results

The systems have been monitored since their installation at June 2005, for the facade, and December 2005, for the park.

Fig. 4 presents the values of the monthly averages of the daily energy produced in the facade, per installed peak power. In general, this system produces more energy in winter periods with a maximum average daily production of 47.3 kWh at November 2007. The production minimum occurred at June 2005 with a daily average production of 20.2 kWh.

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Month

Fig. 4. PV facade — Monthly average of the daily energy produced, per installed peak power.

At Table 3 we present the yearly irradiation and yearly energy produced by PV Facade system. The average yearly irradiation measured in the vertical facade, is about 1 155 kW/m2 and the energy production is about 977 kWh per kW of peak power installed.

Year

Power

Irradiation

Production

(kW)

(kWh/m2)

(kWh/kW)

2006

12.16

1 118

950

2007

12.16

1 193

1 004

Table 3. Yearly energy produced by PV Facade system, per installed peak power.

Solar Mobile Companion

In this project a design concept for PV powered PDA (Personal Digital Assistant) was designed. The design was made with the aim to use the matching model. The main challenge of the project
was to integrate a PV surface larger than the functional product in such a way that it can optimally convert energy and users can conveniently use the product. The final product design is a mobile device that is highly energy efficient. The target group consists of users that have a modest demand for functionality and thus energy consumption. The PV panel is foldable and detachable. Folded, the panel is small enough to fit in the cover of the device. When detached the panel can be left to charge its own battery on a location with high light intensity. The main device can be used on a different, darker, location. As soon as the panel is connected to the device again, the energy stored in the panel’s battery is transferred to the device’s battery.

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A tangible model was made of the product. The final design is a concept, a showcase. It is estimated that the design is technically feasible in terms of technology by the year 2010.

Planning Phase

The first and often most difficult stage of planning a solar cooling plant is to calculate the actual cooling demand. Norm calculations usually give the sum of multiple single peak loads resulting in a very high overall peak load. This demand however will only be required for a very small number of running hours. This explains why electrical cooling machines are mostly over-sized and therefore have to continuously modulate. This unstable operation leads to lower efficiency levels and unnecessarily high power connections.

If a solar thermal cooling plant was to be designed based on these peak loads, the plant would not only be very expensive, the over-sizing also leads to operational problems.

Table 1: Overview of the thermal cooling plants already operational from S. O.L. I.D.

Location/Project

Cooling Machine

Constr.

Cooling

Power

Collector

Area

Pristina — EAR Tower

2 Pcs. LiBr-Chiller

2002/3

70 kW

226 m2

Leutschach — Wine Cooling

Ammonia, Custom — made (Podesser)

2003

15 kW

100 m2

Graz — Buro, Test Plant

Ammonia, Custom — made (Kunze)

2003

2 kW

8 m2

Stadtwerke, Crailsheim

1 Pcs.. LiBr-Chiller

2004

15 kW

Energy from boiler

Brussel — Renewable Energy House

1 Pcs.. LiBr-Chiller

2005/7

35 kW

60 m2

Phonix — Desert Outdoor Center

1 Pcs.. LiBr-Chiller

2006

70 kW

168 m2

Qingdao — Olympic Village

2 Pcs.. LiBr-Chiller

2006

512 kW

631 m2

Tampa — Estellas Restaurant

1 Pcs. LiBr-Chiller

2007

70 kW

210 m2

Lisbon — CGD

1 Pcs. LiBr-Chiller

2008

585 kW

1592 m2

Phoenix-Lanta

1 Pcs. LiBr-Chiller

2008

130 kW

504 m2

Gleisdorf- Service Center Municipality

1 Pcs. LiBr Chiller, and DEC

2008

35 kW 6000 m3/h

260 m2

Graz, office

1 Pcs. Li Br Chiller

2008

17.5 kW

58 m2

All of the cooling projects for air-conditioning purposes were over-dimensioned by a factor of 2-3 during the initial design phase. According to the DIN, the EAR Tower in Pristina had a cooling demand of 210 KW. The actual cooling system installed by S. O.L. I.D. uses two cooling machines with a total nominal capacity of 70 KW (peak 90 KW) and a back-up 30 KW compression cooler. The maximum measured cooling demand over six summers (including the particularly hot summer of 2003) was 80 KW. Same has been monitored on all other projects.

The influence factors on the cooling demand are as well as people, IT equipment, lighting and ventilation, most notably passive solar gains.

A realistic estimate of the cooling demand requires further experience or a simulation programme.

The cooling demand also varies considerably depending on ventilation, in particular rates of air change and heat recovery installations play a big role.

For air conditioning in office buildings, a ratio of 12m2 collector area per 100m2 of office area to be cooled has proven to be relatively accurate. Larger collector areas are necessary only in extreme climates with high cooling demands at night.

Diagram 1: shows measurements from a typical conventional cooling machine in the USA. Notable is that during over 90% of the running hours, the cooling demand was lower than 20% of the installed capacity,

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and 99% of the time lower than 30%.

Diagram 2: This building has a nominal load of 1200 tons, however, even in peak seaseon operation is

image505

mostly between 250 and 500 tons.

Diagram 3 Cooling demand in different Austrian buildings (Source: Fink et al, AEE Intec)

Detailed thermal simulation of classified facade systems

The classification of fa? ade systems by “morphological” aspects, i. e. form, dimension, construction, material, function etc. led to a great variety, (23 parameters and up to six variations per parameter in the morphological box). The number of classified solutions could dramatically be reduced, if only the physical properties were considered, which had an influence on the energy demand. It was possible to reduce the 23 parameters to six energy relevant parameters: window/fa? ade (Awindow), mean heat transmittance of fa? ade (Um), heat gain coefficient of glass (gG), heat gain coefficient of shading devices (FC), light transmittance of glass (TL), equivalent air change rate (neq). For each parameter there are defined five equidistant values, the bandwidth between lowest and highest value given by minimal building standards and best practice solutions (Table 1).

Table 1. Equidistant steps and bandwiths of relevant parameters (U-values of opaque and transparent elements

were combined to a mean faqade value)

north

East

south

west

0,300

0,475

0,650

0,825

1,000

0,150

0,290

0,440

0,580

0,720

0,500

1,080

1,650

2,230

2,800

0,370

0,460

0,560

0,650

0,740

1,0000

0,8125

0,6250

0,4375

0,2500

0,510

0,585

0,660

0,735

0,810

0,180

1,010

1,840

2,670

3,500

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In total there were 15,625 facade combinations to be simulated by TRNSYS for each of the (four) major fa? ade orientations. All simulations were carried out under the same boundary conditions, such as office floor plan and weather data.

Building description and climate

Villa Zagala is located at 34.6° South, 58.5° West, and 26 m over sea level, in “Great Buenos Aires”. There are neighbouring buildings, such as a hospital and a geriatric house and a church that conditionates the orientation of the new building. The climate variables in winter and summer are shown in Table 1. The outdoor air temperatures and wind velocities were obtained from the National Meteorological Service and the mean solar irradiance on horizontal surface was estimated from correlations (Righini et al., 2004).

Table 1. Meteorological data of Villa Zagala, for a winter (July) a summer (January) month.

Month

Min Temp (°C)

Mean Temp (°C)

Max Temp (°C)

Solar Irradiance (MJ/m2)

Wind velocity (km/h)

July

6,2

10,7

16,2

7,93

7

January

17

22,9

28,6

23,62

9

The floor view and two facades are shown in Figures 1 and 2. The original project was a conventional design commonly used by the Ministry of Social Development (MDS) team in these buildings with slight adaptations depending on the site. Due to functional reasons, the CIC building is divided in two independent sectors, named Health and Development, with a covered area around 325 m2 each one. The Health Sector has a large vertical surface oriented to North in order to maximize the solar collection. Originally the vertical envelope was a plastered hollow ceramic wall (0.18m thick), with indoor partitions of 0.15m thick hollow ceramic bricks. The roof was a metal sheet with a gypsum ceiling. This project was modified in order to minimize the thermal losses through the building envelope by improving the thermal insulation of walls and roofs with a polystyrene sheet (0.05m thick), the subfloor with insulating aggregates and double glazing in windows. Reduction of the air leakages through the opening frames, avoiding overheating in summer through solar control devices as overhangs, shading devices, etc., forced and natural ventilation, and daylighting, were also included. Solar and low-energy devices as solar water heating, photovoltaic panels, and low-energy consumption lights, will be installed in the building.

Function as a solar collector

Подпись:
First of all, the collector can be regarded as a fa? ade collector with its typical advantages, disadvantages and special aspects to be considered in order to be designed properly. One of these important aspects is the minimum backside insulation [3, 4] to prevent the room from overheating. In the case of the semi-transparent collector these minimum insulation requirements have to be fulfilled by the inner glass pane(s). Depending on the efficiency of the collector and thus its temperature level, it will be necessary to use a double glazing with Low-E coating as “backside insulation” or multi­layers of transparent foils [7]. Another important topic will be the effect of the openings and the position of the absorber on the natural convection within the collector and thus on its efficiency. In order to have a high flexibility concerning the absorber channel design as well as an aesthetic appearance, roll-bond absorbers (Fig. 4) seem to be a good choice for this type of collector. In conventional absorbers, the heat transfer direction from the absorber surface to the next channel is basically perpendicular to the channel direction. In the case of an absorber with a three-dimensional structure it has to be considered that the heat transfer distance to the fluid is increased and the cross section is reduced: The sides of the lamellae (bent to outside) are not in contact with the channel; therefore the heat transfer is only possible via the remaining flat areas of the absorber which are connected to the channels. The advantage of roll-bond absorbers is the fact that their channel distance can be reduced without additional costs. It can be expected that smaller channel distances will compensate for the lower heat transfer of the three-dimensional structure mentioned above and thus lead to high collector efficiency factors F’ anyway. Moreover, for large sun elevation angles the incidence angle modifier (IAM) of the lamellae should be higher than for a flat vertical absorber. This could be beneficial for solar gains in summer in order to drive a solar cooling system. Roll-bond technology also offers the possibility to realize optimized channel arrangements such as fractal-like, multiply branched FracTherm® structures which lead to a low pressure drop as well as a uniform flow distribution [5, 6]. Even non-rectangular shapes can be used, which might be interesting for architectural reasons.

Regarded as a window-like building component, the three-dimensional structure of the absorber leads to an angular-selective behaviour. Depending on the geometry of the openings and their coating the properties concerning absorption, transparency, daylighting, solar control and glare protection can be adjusted according to the specifications of the particular application. Fig. 5 shows some principal variations of geometry and coating. Variant a) mainly focuses on absorption, transparency, solar control and glare protection, but it will have a poor performance with respect to daylighting since there are no reflecting surfaces leading the sunlight to the inside. In contrast to a), the diffuse reflector of

image441

Variant b) features better daylighting behaviour, but poor absorption, solar control and glare protection. Variants c) and d) can be regarded as compromises of a) and b) with different focuses.

image442

image443

In Fig. 6 different views of a detail of a possible semi-transparent absorber with lamellae and fluid channel are shown. The size of this small part is only about 128 mm x 150 mm. The exterior view in a) gives an impression of the absorber seen from outside, whereas the internal view in b) shows the appearance from inside. It can be seen that for the assumed sun elevation angle a homogeneous shadow is formed (without light stripes from the openings). View c) and d) show how the effective transparency changes with the angle: only small slits appear if one looks through the absorber horizontally, but they seem to become bigger if one looks downwards. This effect is especially interesting for multi-storey buildings.

Fig. 7 shows the absorber detail at different incidence angles of the sun. In the raytracing simulations the absorber was oriented towards south and the solar azimuth angle was always 0. It can be seen that even for small incidence angles the shadow is homogeneous.

Fig. 8 gives an impression of the appearance of an absorber with an area of 1 m x 2 m and its shadow. In this case parallel, vertically oriented channels were assumed. However, other channel designs are also possible.

The typical room

The typical room used for the studies is a standard cross ventilated classroom, 7 x 7 x 2.7 m. The external concrete wall are 16cm thick with three windows for each facades (see Figure 3). Different values of porosity (percentage of openings with regard to the facade) to quantify the

impact on the autonomy in natural lighting. Two azimuths have been considered for the main facades : North and South then East and West

Only a overhang solar shading type has been considered. The TMY weather file used is the one from Saint Pierre, a town located in the south of La Reunion.

The classroom has been divided into three equal strips. The daylight factor and the illuminance level have been calculated for each strip.

image469

Heating and Cooling Degree-Day’s distribution on Mendoza’s Metropolitan Area

The differences between the values of HDD and CDD obtained from the different of measurement sites (urban and rural stations within MMA and the local weather station at the airport) were calculated. These differences were expressed as percentages in order to quantify the error’s magnitude incurred in the calculation of the studied variables when not considering the effect of the city on the local climate.

Table 3. Monthly values of HDD y CDD corresponding to the north transect. Stations 50 vs. 59 and the

Airport’s station are compared. (See figure 1)

Urban Area

Rural Area

Airport

Difference %

CDD

HDD

CDD

HDD

CDD

HDD

U-R

U-A

R-A

January

247

212

226

17%

9%

-6%

February

191

143

178

34%

7%

-20%

March

82

49

76

68%

9%

-35%

April

50

127

100

-61%

-50%

27%

May

142

235

183

-40%

-22%

28%

June

178

310

267

-43%

-33%

15%

July

225

331

282

-32%

-20%

17%

August

200

279

248

-28%

-19%

12%

September

80

178

162

-55%

-50%

10%

October

54

26

0

107%

November

185

146

174

26%

6%

-15%

December

315

228

220

38%

43%

4%

Table 4. Monthly values of HDD y CDD corresponding to the south transect. Stations 50 vs. 40 and the

Airport’s station are compared. (See figure 1)

Urban Area

Rural Area

Airport

Difference %

CDD

HDD

CDD

HDD

CDD

HDD

U-R

U-A

R-A

January

247

180

226

37%

9%

-20%

February

191

127

178

50%

7%

-28%

March

82

40

76

86%

9%

-41%

April

50

131

100

-62%

-50%

31%

May

142

243

183

-42%

-22%

32%

June

178

236

267

-25%

-31%

8%

July

225

337

282

-41%

-20%

17%

August

200

291

248

-39%

-19%

17%

September

80

122

162

-34%

-50%

25%

October

54

23

0

134%

November

185

146

174

27%

6%

-16%

December

315

217

220

45%

43%

-1.5%

Table 5. Monthly values of HDD y CDD corresponding to the west transect. Stations 50 vs. 3 and the

Airport’s station are compared. (See figure 1)

Urban Area

Rural Area

Airport

Difference %

CDD

HDD

CDD

HDD

CDD

HDD

U-R

U-A

R-A

January

247

176

226

40%

9%

-22%

February

191

132

178

44%

7%

-26%

March

82

52

76

60%

9%

-31%

April

50

94

100

-47%

-50%

6%

May

142

219

183

-35%

-22%

19%

June

178

287

267

-38%

-33%

7%

July

225

301

282

-25%

-20%

6%

August

200

290

248

-31%

-19%

17%

1st International Congress on Heating, Cooling, and Buildings, 7th to 10th October, Lisbon — Portugal /

September

80

120

162

-33%

-50%

-26%

October

54

23

0

134%

November

185

142

174

30%

6%

-18%

December

315

195

220

61%

43%

-11%

Table 6. Monthly values of HDD y CDD corresponding to the east transect. Stations 50 vs. 15 and the

Airport’s station are compared. (See figure 1)

Urban Area

Rural Area

Airport

Difference %

CDD

HDD

CDD

HDD

CDD

HDD

U-R

U-A

R-A

January

247

217

226

14%

9%

-4%

February

191

170

178

12%

7%

-4%

March

82

60

76

37%

9%

-20%

April

50

89

100

-44%

-50%

11%

May

142

201

183

-29%

-22%

9%

June

178

263

267

-32%

-33%

2%

July

225

279

282

-19%

-20%

-1%

August

200

259

248

-23%

-19%

4%

September

80

96

162

-17%

-50%

-40%

October

54

23

0

134%

November

185

147

174

26%

6%

-15%

December

315

164

220

92%

43%

-25%

The results show that during summer time there exists an underestimation in the cooling demand calculated from the data obtained by local weather stations that oscillates between 6% and 43%. For the winter time, it happens oppositely, an overestimation of the heating load that represents an error from about 19% to 50%.

In the case of the air temperature behavior in downtown respect to its surroundings, it is observed that the demand for cooling in the downtown area is higher than 12% and up to a 130% respect to the surroundings demands, depending on the month of a year and the zone of the city analyzed.

The demand of heating for downtown area respect to the environs is smaller in the order of 25 to 62%.The energy requirements of the suburban and rural zones of the city respect to the values calculated from the local weather station show an overestimation of 4% to 41% of the cooling necessities, and an underestimation of 2% to 32% in the case of the heating demand.

Figure 3 shows the yearly distribution of HDD and CDD within the AMM. The degree day’s distribution responds clearly to the thermal behavior and to the climatic conditions that prevail in the city. During the summer the radiation levels are high, for this reason the materials that compose the ground of the city’s out-skirts, which are mainly rocky, accumulate heat during the day, homogenizing the distribution of temperatures between downtown area and the city’s out-skirts of the. This does not happen in winter due to the lesser amount of radiation during the day, increasing the temperature differences between downtown and the rural areas.

The greater demand in refrigeration during the month of December can be explained by the increase of the anthropogenic contribution in the city, because this is a festive month, whereas January and February are months of vacations. The maps that show the distribution of heating and cooling degrees-day within the AMM always display a hot zone of greater demand of refrigeration and minor demand of heating coincident with the administrative-commercial zone in the city.