1796 World Renewable Energy Congress VI (WREC2000)

© 2000 Elsevier Science Ltd. All rights reserved. Editor: A.A.M. Sayigh

A TRNSYS SIMULATION TO STUDY EFFECT OF EXTERNAL FIXED HORIZONTAL LOUVER SHADING DEVICES ON SIZING OF COOLING AND HEATING SYSTEMS FOR BUILDINGS

GOURI DATTA

Physics Department, Deshbandhu College, Kalkaji, University of Delhi New Delhi 110019, INDIA

ABSTRACT

In most parts of the world both cooling in summer and heating in winter are necessary to maintain thermal comfort conditions inside a building. This paper investigates the effect of fixed external horizontal shading devices on the sizing of heating and cooling devices of a building by TRNSYS simulation, in which a shading routine has been added. This is done for 4 cities of Italy viz Milano, Roma, Napoli and Palermo whose weather ranges from moderately warm to very warm summer, and cold to moderately cold winter conditions. It was found that percentage of size increase for heating in winter is very small as compared with air conditioner size reduction for cooling in summer. In fact about 15 to 19% of size reduction for cooling is achieved by using the appropriate shading devices. This is a very large value, particularly when one remembers that capitol costs for cooling systems are far higher than those of heating systems of same size. So in terms of price of installation, although putting a shading device might marginally increase the cost of heating, the more substantial reduction in cost of cooling would more than compensate it. Therefore installing proper shading devices has an overall positive effect so far as sizing goes.

KEYWORDS

Passive cooling; fixed external shading; louvers; TRNSYS; simulation.

INTRODUCTION

Buildings in most countries around the world require heating in winter and cooling in summer to maintain thermal comfort condition inside, which means the use of heaters and airconditioners. Before installation these heating and cooling systems are properly sized for effective performance. Sizing is important because it is related to the price of the systems for the end user, a small size means lower capitol costs.

To cut down the size of the cooling device proper shading of the windows could be adopted, which would reduce solar gains through windows. However reducing size of air conditioner by shading might adversely affect size of heating unit, so both factors should be investigated.

With this in mind, a study was done to determine the thermal performance of a building by TRNSYS simulation [TRNSYS, 1992 and IISiBat, 1997] using PREBID [PREBID, 1997] in IIsibat environment

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[HSibat, 1996] in which a shading model for windows was incorporated which would demonstrate the effect of various shading devices on building performance. This was done for four different locations in Italy viz. Milano, Roma, Napoli and Palermo in order to study the effect of the shading device for each location.

COMPONENTS USED IN THE TRNSYS SIMULATION

Shading Devices

Fixed shading devices are generally used on the external face of glazing since they lower direct radiation from reaching the internal ambient, dissipating the heat to outside. Therefore they are more efficient than internal fixed shading devices which dissipate the heat to the air gap between shading device and glazing.

The shading devices adopted in this study were external fixed horizontal louvers used on the south window as shown in fig 1.

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Fig. 1. Horizontal louver shading devices.

3 types of this shading device were used defined by, s/I ratios, They are: type sl where s/I = 1, type s2 where s/I = 2, type s92 where s/I = 0.92

Different tilts (ct) of these shading devices with respect to the horizontal were considered: ct = 30 °, 45 °, 60 ° and 90°-i.e. slats closed.

The Building

A simple 2 Zone building was considered as shown in Fig 2, with 3 windows in each zone. The shading is put on the south window in zone 2. The roofs are slanting N & S with a view factor of 0.8 to the sky.

Some other details of each Zone are: Heating set-point temperature: 20°C, Cooling set-point temperature: 26°C Gains : 2 persons doing light work, equivalent to 150 watts/person, Lighting and other appliances: 500 watts, Infiltrations: 0.6 volume/hr.

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NOrth

I I

Zone 1

Zone2

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Fig. 2. Plan of the simulated building.

New Routine for Characterization of Shading Devices

The routine developed by the WIS group, LOUVER. DLL (Coronei et al.0 1995) was used to study the effect of shading by louvers on the south window of the building. It generates 19 by 19 matrices for the primary and secondary transmittance of the shading device. This routine was linked to the TRNSYS program with a small subroutine to make it compatible with TRNSYS.

RESULTS

The TRNSYS simulation for an entire year was done on an hourly basis for 4 different locations already mentioned, the three specific shading devices set at different tilt angles. The annual outputs were studied for both cases of shaded and unshaded building and the peak cooling and heating power requirements were determined for each location. It is found that peak heating power does not change much with various shades. For Milano and Roma there is hardly any change, and even for Napoli and Palermo the change in peak heating power with different shading devices is not much. In the case of cooling peak power, the effect of shading is much more. Figure 3 illustrates this for Rome.

To illustrate the effect of shading on sizing more effectively, graphs were plotted with percentage cooling and heating system size variation due to different shading devices with no shading as the reference case. Figure 4 demonstrates the size variation for Roma. The results show that percentage of size increase for heating is very small compared to that of cooling. In fact about 15 to 19% of size reduction of cooling unit can be achieved by using appropriate shading devices in the different locations, a substantial value, particularly when one remembers that capitol costs of cooling systems are far higher than those of heating systems of same size. So in terms of price of installation although putting a shading might marginally increase the size of heating system to be installed and its cost, the more substantial reduction in size of air conditioner and also its cost would more than compensate it. Therefore installing proper shading devices have an overall positive effect so far as sizing goes.

REFERENCES

Coronel J.F., Molina J.L., Alvarez S.(1995) Routines for The Characterization of External and Inter- Plane Louver Shading Devices. Presented at the October 1995 meeting of the commission of European Communities.

IISibat Manual (July 1996) CSTB Sophia Antipolis, France.

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Introduction to TRNSYS for Windows with IISiBat (July 1996 updated to November 1997) Solar Energy Laboratory, University of Wisconsin, U.S.A.

PREBID Manual (April 1997) Transsolar Energietechnik GmbH, Germany. TRNSYS A Transient Simulation Program, Version 14.2 (1992) Solar Energy Laboratory, University of Wisconsin, U.S.A.

ACKNOWLEDGEMENT

The author would like to express her appreciation to ENEA - Cassaccia, Rome where this work was carried out, to Dr. Augusto Maccari of ENEA for all help rendered, and also to ICTP Trieste Raly for funding the Project.

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Fig 3. Variation of peak load power for Roma

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Fig 4. Cooling and heating systems size variation for Roma