داده های ثبت شده دو ساله برای یک سیستم پمپ حرارتی با منابع چندگانه: تجزیه و تحلیل عملکرد

The concept of a low energy building in a temperate climate (according to the Koppen climate classification) is based upon the following principles: reduction of heat losses through enhanced insulation; the inclusion of heat recovery on mechanical ventilation; and the use of high efficiency heating/cooling systems integrated with renewable technologies. It is almost impossible to achieve optimum results in terms of global energy efficiency if one of these elements is omitted from the design. In 2009, a new school building, integrating these three key elements, was opened in Agordo town, located in northern Italy. The main design features of the building incorporate a well insulated envelope and a space heating and ventilation system driven by an innovative multisource heat pump system. Outdoor air is a common heat source, although it does have widely documented limitations. Heat pump systems can utilise more efficient sources than air, including those of ground heat, solar heat, and heat recovery. The installed system within the school building incorporates these three sources. A multisource system aims to enhance the performance of the heat pump, both in terms of heating capacity and overall efficiency. The present work includes evaluation and analysis of data obtained through real time monitoring of the working system in operation, for a period of approximately two heating seasons. During this time, the behaviour of the system was assessed and the incorrect settings of the plant were identified and subsequently adjusted as required. The energy balance indicates that the integration of different sources not only increases the thermal performance of the system as a whole, but also optimizes the use of each source. Further savings can be obtained through correct adjustment of the set point of the indoor temperature. During the final stage of the study, the total energy consumption of the new building is calculated and compared to that of the former building that housed the same school, which had similar dimensions.

There are many ways to reduce the energy needs and heating/cooling capacity of a building. In a temperate climate (as defined by the Koppen [1] climate classification), the following options are considered to be appropriate: - to design a low energy building envelope with good thermal insulation; - to choose energy effective technologies based on a high efficiency generation system, such as heat pumps; - to integrate design and systems with heat recovery devices and renewable energy sources wherever possible. These three features have been incorporated into the new High School Building of Agordo, situated in the province of Belluno, northern Italy. This building was designed in 2006–07, and was occupied in autumn 2009. It is operated by the Belluno Province Administration, an organisation appointed by the public education service. The town of Agordo lies in a valley at 611 m above sea level, in the geographical area of the Dolomiti Mountains, where the climate is severe during wintertime (3376 degree-days). In terms of dimensions, the building has a total floor area of 5680 m², an outward surface area of 13,608 m², and an enclosed gross heated volume of 19,644 m³. The envelope is well insulated, with the outer walls and the roof allowing for an average thermal transmittance of approximately 0.16 W/(m² K), the floor having a thermal transmittance to the ground [2] of 0.4 W/(m² K), and the glazing system having a thermal transmission of 1.38 W/(m² K). From an architectural and functional point of view, the building comprises of two main wings and a central belt, as it can be seen in Fig. 1. The south-east wing has three storeys and houses teaching rooms, used mainly (but not solely) in the morning. The west wing has two storeys and houses the laboratories, used mainly (but not only) in the afternoon. Finally, the three storeys of the central belt house the administrative offices which are occupied constantly throughout each day, and the auditorium, which is used occasionally. Full-size image (29 K) Fig. 1. Photo of the building (view from south). Figure options The school is closed from the middle of June to the beginning of September. The climate management system therefore provides ventilation and space heating, but there is no requirement for summer cooling. Through dynamic simulation using the TRNSYS environment, different solutions were evaluated with respect to the heating system [3] and [4]. A multisource gas-fired absorption heat pump system has been designed to fulfil the needs of the building, utilising ground and solar energy, with recovery on ventilation. The heat pumps selected are Robur GAHP-W-LB type. A full system evaluation was undertaken at the design stage, in order to select the most viable mixed solution, and to optimize the size of both the borehole ground exchanger field, and also the solar system [5]. The efficiency of the absorption heat pump is called GUE (Gas Utilization Efficiency), that is the ratio between the useful thermal output ECA and the thermal input Ein; usually this figure is around 1.2–1.5. The efficiency of a compression heat pump is called COP (Coefficient of Performance), that is the ratio between useful thermal output EC and the electricity input Eel; usually this figure is around 3–4. From the First Law of Thermodynamics, the heat amount coming from the heat source is the difference between the output and the input (whatever thermal or electric). So in heating mode, the ratio between the thermal input from the heat source and the thermal output to the heat sink is much lower for an absorption heat pump (around 0.2–0.3) than for a compression pump (around 0.6–0.8). The latter would therefore require a larger, and consequently more expensive, borehole field.

The paper described the operation of a multisource heat pumps system and explains a methodology for the performance analysis of the HVAC plant. Given the monitored data available it was possible, by means of the First Law balances, to perform a detailed analysis of the behaviour of the system. The integration of different heat sources remarkably increases the efficiency of the system in terms of primary energy consumption. The solar heat contributes with a meaningful fraction of the space heating need, and the use of the solar source to the evaporator of the heat pumps plays a key role in rising up the heat pump performances. The ventilation recovery downstream the cross flow heat exchangers supplies a large share of the evaporators' energy need for ventilation dedicated heat pumps.