Sep 18, 2001 - study shows that hydronic radiant cooling systems in many buildings are ... In cooling conditions the comfort range, for an activity ... 1.0 clo 1.2 met ... There is therefore a need to evaluate the number of hours the comfort conditions are ... first probe is a temperature sensor shaped like an ellipsoid (50mm x ...
Field Measurements of Thermal Comfort Conditions in Buildings with Radiant Surface Cooling Systems MICHELE DE CARLI, PhD Student, Dip. di Fisica Tecnica, University of Padova, Italy BJARNE W. OLESEN, Head of Research and Development, Wirsbo-VELTA GmbH &Co. KG, Norderstedt, Germany
ABSTRACT The performance of radiant heating systems (floor heating, ceiling panels) is relatively well documented. Water based systems, where pipes are embedded in the building structure, are now being increasingly used for cooling purposes. Several theoretical studies based on the use of computer simulations have been published, but very little is reported on the actual performance in existing buildings. There are still uncertainties on how such systems operate and on how well the space temperatures under varying external and internal load is kept within the comfort range. To study this aspect, field measurements of thermal comfort conditions were made in several buildings with radiant surface cooling systems. The systems comprise floor cooling, wall cooling and cooling with pipes embedded in the concrete slabs between each floor in a multi storey building. Long term measurements of operative, air, surface, system and external temperatures have been carried out. The analysis of the data shows that, for the major part of the time of occupancy, the operative temperature is inside the comfort range. The analysis has been lead for different classes of comfort according to existing standards. The data show an increase in space temperature during the day, which is counterbalanced by a corresponding decrease during the night. This study shows that hydronic radiant cooling systems in many buildings are an interesting alternative to full air conditioning systems, for obtaining acceptable indoor thermal environments during summer.
1. INTRODUCTION In the eighties and nineties the market for radiant cooling panels increased significantly in middle Europe. From the middle of the nineties interest in radiant floor cooling started and from the end of the nineties the so called “active thermal slab” have been installed in several multi-storey buildings. Up to now papers presenting theoretical studies of this new technology have been published (Brunello et al. 2001, Hauser et al. 2000, Simmonds et al. 2000, Koschenz, Meierhans and Olesen 1999, Meierhans 1996). At the beginning of 2001 more than 60 buildings with the active thermal slab technique are in operation or being constructed in Germany. Most of them are office buildings with a floor area between 250 m2 and 40.000 m2 but also other type of buildings like museums, hospitals, schools are build with embedded cooling systems.
Clima 2000/Napoli 2001 World Congress - Napoli (I), 15-18 September 2001
Field measurements of thermal comfort conditions in buildings with radiant surface cooling systems
During the last three years temperature measurements on some buildings have been made in order to investigate the performance of different radiant cooling systems. In the present paper measurements from three buildings are presented.
2. METHOD In monitoring existing buildings the evaluation of energy consumption, operating conditions of the air conditioning system and thermal comfort satisfaction of the occupants should be investigated simultaneously. Measurement and evaluation of the thermal comfort conditions are therefore focussed. Evaluation criteria from different national and international standards are used. 2.1 Thermal comfort evaluation Comfort requirements can limit the capacity of the radiant heating and cooling systems. On the basis of the international standards and guidelines (ISO 7730 1994, CR 1752 1998, DIN 1946 Part 2) the comfort range for operative temperatures is between 20°C and 24°C, for people with sedentary activity level (1.2 met) in heating conditions (winter), with clothing thermal resistance equal to 1.0 clo. In cooling conditions the comfort range, for an activity level of 1.2 met and a clothing thermal resistance of 0.5 clo, is 23°C to 26°C. These ranges are based on a predicted percentage of dissatisfied (PPD) below 10% and a predicted mean vote (PMV) between –0.5 and +0.5. For radiant systems it is very important to refer to the operative temperature, both for evaluating the comfort conditions and the performance of the system itself.
Figure 1 - Requirements in the German Standard DIN 1946-Part2. Horizontal Dashed Zone: Cool Range. Crossed Dashed Zone: Comfort Range. Vertical Dashed Zone: Warm Range.
Thermal active slab systems are using the thermal storage of the concrete slabs to reduce peak loads and transfer some of the cooling to outside the time of occupancy. This has a dynamic effect on the thermal characteristics of the indoor environment, i.e. the operative temperature will often increase during daytime. In the German standard DIN1946 the space
Clima 2000/Napoli 2001 World Congress – Napoli (I) , 15-18 September 2001
Field measurements of thermal comfort conditions in buildings with radiant surface cooling systems
temperature may increase to 27°C with outside temperatures of 32°C (see figure 1) In order to maintain the comfort conditions in the range above mentioned there is a need to know the external and internal loads and the capacity control of the thermal active slab. In EN ISO 7730 and CR 1752 the comfort criteria for the temperature level inside is given as a range for PMV or PPD. Depending on economy and outside climate not all countries will design for the same comfort level. Also depending on the type of building there may be acceptance to design for different levels of comfort. Therefore CR 1752 and a proposed revision of ISO 7730 introduces three classes as shown in Table 1. The standards give values for the comfort conditions in steady state conditions, but according to Knudsen (1989) the PMV-PPD index can be used as long as the rate of temperature change is lower than 5 K per hour. Table 1: Classes of Thermal Comfort (CR 1752) Class Comfort requirements
Temperature range
PPD
PMV
Winter 1.0 clo 1.2 met
Summer 0.5 clo 1.2 met
[%]
[/]
[°C]
[°C]
A
