Abstract
New and refurbished buildings have to relate to ever increasing standards regarding energy efficiency and energy consumption. This results in well insulated building envelopes with low air leakages offering reduced heating demands. One of the downsides of this is that these buildings are easily warmed up to such a degree that in order to sustain an acceptable indoor climate, removal of excess heat becomes a necessity. The removal of surplus heat is often done through means of mechanical cooling. However, energy consumption related to mechanical cooling is considered incompatible with achieving zero energy buildings (ZEB). As a response, the use of Ventilative cooling (VC) solutions is settling, and it is by many considered crucial in realizing ZEB. Ventilative cooling refers to the use of ventilation air in order to reduce or eliminate the need for mechanical cooling. VC can be applied through both mechanical and natural ventilation strategies, as well as a combination. To achieve efficient VC while ensuring an acceptable thermal climate, the first step is to include measures that provide minimization of heat gains.
This paper examines the application of ventilative cooling solutions in cold climates through simulations of an already existing kindergarten in Norway. This kindergarten has a mixed-mode ventilation system integrating mechanically balanced ventilation with natural ventilation from motor controlled windows. In this paper this kindergarten has been analyzed by means of energy use and thermal comfort with IDA ICE program. The validated simulation of the kindergarten has been compared to simulations of the same kindergarten using DCV and VAV (both without cooling) and hybrid window ventilation and exhaust fan and only window controlled natural ventilation(these two last with night set back allowed). Results show important energy savings when using ventilative cooling as outcome of the low outdoor temperatures and the same applies for night cooling. Simulation results indicate that solutions like hybrid could cut the annual energy consumption by as much as 13 % compared to conventional mechanical ventilation. When looking at the thermal environment and indoor temperatures, it is found that for really warm days, it is hard to sustain acceptable temperatures without the use of night set back or mechanical cooling otherwise. Ventilative cooling is proven to be relevant to highly occupied buildings and will be crucial to achieving energy targets for renovated or new zero energy buildings while the indoor climate is maintained.
Abstract
The substantial reduction of required heating load in passive house buildings has led to an integration of heating in the ventilation system by post-heating the supply-air, called air-heating. The incorporation of heating in the ventilation system constitutes a departure from a well-established customary practice of strictly separating heating and ventilation in the indoor climate design. It is therefore imperative to thoroughly investigate and evaluate air-heating with regard to effects on the indoor air quality (IAQ) and thermal comfort. Simulations and laboratory measurements suggest that air-heating has no adverse effects on IAQ and thermal comfort. The purpose of this paper is to investigate the acceptability and suitability of air-heating from the occupants' point of view. A comprehensive literature study is performed in order to assess the perception of IAQ, thermal comfort and general experiences with the operation of air-heating in comparison to other heating strategies. The evaluation is based on studies on multifamily passive house buildings in temperate and continental climates. No proof for the general unsuitability of air-heating in residential passive house buildings with regard to perceived IAQ and thermal comfort was found, but clear limitations were determined in buildings where the heating is based on air-heating only. Based on the findings it is suggested that air-heating always should be supplemented with an extra heat source in bathrooms and it should be possible to adjust the supply-air temperature in the bedroom independently from other rooms.
Abstract
In highly-insulated buildings such as passive houses, the space-heating distribution subsystem can be simplified by reducing the number of heat emitters. In this context, the bi-directional flow through open doorways is known to be an efficient process to support the heat distribution between rooms. This process is therefore investigated using field measurements within a Norwegian passive house. The so-called large opening approximation proves to model fairly the mass flow rate, but also the convective heat transfer if the thermal stratification is accounted for. Furthermore, the discharge coefficient appears to be independent of the heater type and location in the room.
Abstract
Realisation of Zero Energy Buildings (ZEB) for residential use cannot succeed without: minimising leakages, increasing thermal insulation and using reliable and energy efficient system solutions. However, very airtight houses may have a negative impact on thermal comfort and indoor air quality. Focussing on ventilation systems then becomes a requirement.
In cold climates, temperature differences between indoor and outdoor air often exceed 40 °C during winter. State-of-the-art heat recovery systems may not be able to handle these differences while providing proper air quality and preventing excessively dry indoor air.
The present study of energy recovery systems focuses on apartment buildings located in cold climates countries using central air handling units. Heat exchangers recovering sensible heat are compared with energy exchangers with recovery of both sensible and latent heat. For the latter, both adjacent and non-adjacent solutions are considered.
A specific net energy savings factor is developed taking into account the energy recovered, but also the pressure drops and the variation on the effectiveness of the fan given the installation of the heat/energy recovery.
Heat exchangers are efficient and reliable. Recuperative heat exchangers normally imply no air quality problems, but have severe freezing problems. Regenerative heat exchangers encounter small freezing problems, but do not prevent transfer of odours from extract air to supply air. Regenerative energy exchangers provide an efficient heat and moisture exchange between exhaust and supply air flows, diminishing ice formation and the humidification requirement for indoor air.
Experience with low-energy and passive house buildings forms the basis for the further development of zero-emission buildings. A post-occupancy evaluation of the Løvåshagen cooperative is therefore conducted by means of user surveys and measurement of indoor climate parameters, energy use and window opening time.
The goal of the post-occupancy evaluation is to obtain information about how occupants use and experience low-energy and passive house dwellings, especially with regard to heating and ventilation. In addition, the impact of user behavior on the indoor climate and energy use will be assessed.
In this paper, the results of the user survey regarding user habits and occupant satisfaction are presented.
The results show that low-energy and passive house apartments are used in ways that have a substantial impact on the indoor climate and energy use. The assessed extent of window ventilation and use of floor heating throughout the year around definitely increase energy use substantially and therefore partially explain the difference between the calculated and measured energy use. This difference will be quantified by measurements and parametric simulation in the continuation of the study.
Most respondents are satisfied or very satisfied with living in a low-energy or passive house dwelling. Nevertheless, a clear need for improvement with respect to heating and ventilation systems is detected.
It can be concluded that increased attention to the interaction between the occupant, the building design and the technical installation is needed in the development of zero-emission buildings.
The German definition of the passive house standard is strongly related to the air-heating (AH) concept, while this concept is not explicitly connected with the Norwegian definition (NS 3700 standard). As AH presents an opportunity for space-heating (SH) simplification, the AH potential is here investigated in the Norwegian context. The questions of the required AH temperatures, of the temperature distribution between rooms and the influence of losses from ventilation ducts are investigated using detailed dynamic simulations (here using TRNSYS). This is done using a typical detached house typology, both considering different building construction materials as well as different climate zones (Oslo, Bergen and Karasjok). Simulation results present the potential and limitation of the AH for this common building typology but also enable to derive guidelines for the proper design of AH systems in Nordic conditions. For example, the standard SH design conditions (STD) appear to be the most severe conditions in term of AH temperatures and uneven temperature distribution between rooms.