The change in climate and the rise in energy rates have become a necessary consideration in the construction industry which has made architects and engineers to arise with improved building design concepts. A focus on creating a comfortable indoor climate in administrative buildings ensures productive working conditions for the users. Specific climatic design principles are often disregarded when designing to create a comfortable indoor climate. Western architecture is transferred to different climatic zones to replaced native/vernacular architecture without adjustments which results to buildings that do not provide adequate comfort. Building core activation is a System used in temperate climatic regions to provide a comfortable indoor climate for administrative buildings by making an interesting use of geothermal energy. This paper explains the effect of climate on the use of building core activation in administrative buildings (climatic condition of Cyprus as case study).
Keywords:
Building core activation, Thermal comfort, Condensation, Thermal activation, Relative humidity
1.1 INTRODUCTION
The need for a better thermal performance is progressively taken into consideration in the programming and design of Administrative buildings. With several interest about change in climate , stern guidelines to meet sustainability targets, the inclination to design energy-efficient buildings continues to arise. An energy-efficient way to design is to use building core activation System. The system uses the thermal mass of the building to create an efficient cooling system. The concrete extracts the heat during the day, maintaining a cool interior. It is a system that is progressively being used for administrative buildings in temperate regions.
The system comprises of water carrying tube transporting either cold or hot water that makes an remarkable use of environmental energies such as ground soil, ground water and air to activate thermally, the building for summer or winter periods. This cooling concept of water carrying tube systems which are installed in the core of the building is called the building core activation.
Plate 1: water carrying tubes embedded in concretes core
The concrete slabs are activated with heating or cooling energy by means of hot or cold water distributing through the heat exchangers incorporated in the building element. The circulation of water flows through the tube system transferring heating capacity or cooling capacity to the concrete slab, therefore cooling or heating it, depending on the water temperature. The stored energy in the concrete core is then transferred to the room during several hours through 60 % radiation and 40 % convection.
However, Installations in cold climatic zones are constrained principally by heating capacity of the system while using the system in the hot and humid climate is restricted by need to avoid condensation. Operation of the thermally activated elements effectively reduces the size of the ventilation system. It is not designed to take out cooling loads or heat the building but only deliver fresh air for the occupants. This indicates that lower air change rates can be used. If cooling is done slightly, supply air can also offer some extra cooling, when it is. This leads to the research question, “is the principle of building core activation efficient and sustainable in the warmer climate of Cyprus”
1.2 Aim
This paper aims to analyze the use of building core activation in administrative buildings and its compatibility for the climatic conditions of Cyprus.
1.3 Scope
The scope of the research is limited to the use of building core activation in Cyprus during its long summer period (Famagusta climate to be taken as a case study).
1.4 Methodology
Published literature reviews containing successful experiments in the use of building core activation served as a basis for this paper research.
2.0 MATERIALS AND METHODS
In Studies done by Meierhans (1993), system with pipes integrated in the slab constructions of office buildings for heating and cooling was established. Simulated results were presented for an office building in Horgen, Switzerland. The result shows that the indoor temperature was maintained at a satisfactory range even at hot outdoor conditions. Computer simulations of heating or cooling system with pipes integrated in the concrete slabs between the floors in a multi-storey building were carried out by Hauser et al. (2000). The simulated system supplied or removed the heat from the space by heated/cooled water flowing in the pipes. The results showed an improvement of thermal comfort by reducing the annual maximum working temperature by 10 K (39°C – 29°C) compared to no cooling. In addition, in the dynamic simulation done by Olesen and Dossi (2004) the working temperature was within the range 22–25°C during most of the operational hours. The ranges of operational temperatures were adequate to meet the requirements of the current standards.
Nonetheless, the barriers were found out in the following context:
It was found that the effect of passive utilization of the thermal mass is dependent on the climate context. The thermal properties of the passively used thermal mass elements and surrounding environment should be considered to exert its storage ability. The surface area of the element needs to be adequately large to guarantee enough heat transfer rate.
The system is suitable for buildings with low heat or cooling loads (40 – 50 W/m2). High thermal insulation of the building envelope and proper solar shading devices are necessary.
For effective operation of the system, there should be a balance between heating losses and cooling loads. (The same heat exchange surface is used for both cooling and heating)
2.1Case study
Centre for Sustainable Building, Kassel, Germany
The office building belongs to the Centre of Sustainable Building (ZUB), University of Kassel, Germany. The building shows an example of an innovative low temperature heating or cooling systems implementation. The office building consists mainly of three different zones: A zone for exhibitions and events, one zone for offices and an experimental zone for different kinds of research in innovative building technologies and building services concepts. Building core activation system is used for heating and cooling of the offices. In the case of heating operation mode, the system works with water inlet temperatures controlled according to the outdoor temperatures (approximately 24°C). In case of cooling need, pipes integrated in the floor slab of the basement are used as a ground heat exchanger. The use of Mechanical cooling is not necessary.
Plate 2: The Centre for Sustainable Building (ZUB) in Kassel, Germany
3.0THEORY
3.1 Climate analysis of Cyprus
Cyprus has a warmer climate with the typical seasonal rhythm strongly noticeable in respect of temperature, weather, rainfall and generally. Hot dry summers starting from mid-May to mid-September and rainy, rather changeable, winters from November to mid-March are separated by spring and autumn seasons of rapid change in weather conditions
3.1.1 Air Temperatures
Cyprus is characterized with mild winter hot and summer but this generalization must be modified by consideration of altitude, which lowers temperatures by about 5 C per 1,000 metres and of marine influences which provide cooler summers and warmer winters near most of the coastline ,especially, on the west coast.
Between mid-summer and mid-winter temperatures is a seasonal difference quite large at 18 C inland and about 14 C on the coasts.
Maximum day temperature and minimum night temperature are also quite large especially inland in summer. These differences in temperature are in winter 8 to 10 C on the lowlands and 5 to 6 C on the mountains increasing in summer to 16 C on the central plain and 9 to 12 C in a different place.
The mean daily temperature in July and August ranges between 29 C on the central plain and 22 C on the Troodos mountains, while the average maximum temperature for these months ranges between 36 C and 27 C respectively. The mean daily temperature in January on the central plain is 10 C and 3 C on the higher parts of Troodos Mountains with an average minimum temperature of 5 C and 0 C respectively.
3.1.2 Relative Humidity
The altitude above mean sea level and distance from the coast also has significant effects on the relative humidity which is a reflection of temperature differences. Humidity during winter days may be described as average or slightly low at 65 to 95% and at night throughout the year. Humidity is very low with values on the central plain usually a little over 30% and occasionally as low as 15% near midday in summer
3.2 CASE STUDY: CLIMATIC CHART ANALYSIS FOR FAMAGUSTA
4.0 RESULTS
In the heating mode using the Building core activation systems, surface temperature of the concrete is no higher than 28°c while in cooling mode, surface temperature is no lower than18°c. During cooling mode using the building core activation, the emitting surface is set to a lower temperature than the indoor temperature thereby absorbing the heat in the room to its surface.
Plate 3: cooling mode of the system
From the climatic chart/analysis, Famagusta is seen to have hot humid climate. Its relative humidity ranges from 52% to 62% and air temperature ranges from 23°c to 34°c in summer period as the chart describes. There is a higher cooling demand from mid may to mid September with it lowest in temperature in May at 28°c with a corresponding relative humidity of 59% and its highest temperature in July at 34°c with corresponding relative humidity of 52%.
Deductions from the chart show relative humidity to be above 50% in the hot summer months where cooling demands are higher. It can be deduced that using building core activation in its cooling mode which is between 18°c to 23°c would result in a rapid increase of indoor air relative humidity when in contact with the cooled surface. Condensation has a high risk of occurring on the cooled surface when the indoor air reaches its dew point which is one of the pitfalls mentioned earlier on in this paper in hot humid climate.
Condensation on the cooling surface happens when the warm air being absorbed comes in contact with the cooled surface thereby dropping the temperature of the warm air suddenly. As a result of the sudden drop in temperature of the warm air, its relative humidity increases and the air reaches its saturation point quickly thereby resulting to condensation occurring on the cold surface.
5.0 DISCUSSIONS/CONCLUSION
It can be deduced from the result that condensation is a disadvantage in the use of building core activation for cooling during summer periods in Famagusta. To avoid condensation on a cooled surface, if this cooling system is to be adopted, there is a need to take account on the limitation on water temperature, based on the space dew temperature. The supply water temperature, average water temperature or flow rate may be controlled from zone to zone. So therefore a zone control is suitable to use. In particular cases regarding well designed systems with low cooling or heating loads, a concrete slab can be controlled to a constant core temperature year round. If for example the core is maintained at 20°c it will cool when the room temperature is above 20°c and supply heat when the room temperature is above 20°c if the system is used for heating. However if concrete slabs are maintained at constant temperature, the surface temperature and absolute humidity must be controlled by setting the lower limit for the supply water temperature to equal the dew point temperature (absolute humidity in space). When the dehumidification is performed by a ventilation system the cooling capacity can also be increased.
Intelligent use of building core activation in administrative buildings may lead to a reduction of high power demands at night by saving energy and releasing it in daytime. The heat gains during occupancy are piled up in the active structure component and are extracted at night by circulating cool water or by free night cooling. Therefore, a considerable peak shaving can be achieved by moving partial loads to nighttime. A dynamic computer simulation was used to study summer performance based on time of system operation, and supply water temperature by Olesen in an earlier study. It was found that the system operation at night was satisfactory and supply of water temperature can controlled over the season based on outside temperature. Therefore the use of this cooling system can be advantageous and recommended if the condensation risk precautions are being practiced. The application of the system in other region of Cyprus could be sufficient because the low relative humidity in summer which are as low as 15%