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This paper investigates experimentally the cooling performance of a concept, where the radiant ceiling is suspended from the hollow-core concrete slab and by ventilation supply in the plenum and the perforations of the ceiling tiles, ventilation air is distributed without ducts and air terminals to the occupied zone. Literature has proven that this concept allows for more streamlined installation procedures and excellent performance in terms of thermal comfort and draught. The paper reports experimental results from a climate chamber, where the concept was tested under both steady-state and quasi-steady conditions. The steady-state conditions were chosen to map the cooling performance with different air change rates, and different ventilation and water supply temperatures. The results showed that for air change rates of 3 h−1 in the occupied zone and water supply temperature of 17 °C, the cooling output from the ceiling increased by 10 %. The concept was also tested under quasi-steady conditions in a 48 h cycle to quantify the thermal buffering effect of the exposed upper concrete slab when subjected to ventilation supply air. The effect amounted to 11–12 % increased cooling capacity at the end of the working day when the driving temperatures between air, water and thermal zones were at their maximum.

Storage tanks are commonly used for domestic hot water (DHW) preparation in large buildings supplied by district heating (DH), especially to cope with peak demand. The charging control of DHW tank systems is often suboptimal, increasing return temperatures and harming the overall DH operation efficiency. This paper presents two novel control concepts to optimise DHW tank charging, satisfying comfort and hygienic requirements without leading to excessive DH flows. The first, more complex control concept employs the smart energy meter sometimes used for DHW billing. It inspired the development of a second, broadly implementable control concept employing a staged proportional gain with an added temperature sensor. The authors tested and refined this staged-gain concept using a validated Modelica model of a real DHW system in a Danish multistory residential building. The authors subsequently implemented the staged-gain control concept in the field, successfully reducing the energy-weighted DH return temperature by 7 °C and the total DH flow by 23.6% compared to the conventional thermostatic control. This analysis accounted for the variation in DHW tapping, DHW temperature, DH supply temperature, and cold water temperature. Furthermore, the performance was robust to relaxed settings of the valve constraints, demonstrating minimal configuration requirements for new implementations.

Roof windows are efficient and flexible daylight sources that are essential in certain types of houses if they are to achieve sufficient daylighting throughout. Previous studies have indicated that, for such buildings to meet nearly zero-energy targets in an easy and robust way without compromising on daylighting and thermal comfort, the thermal properties of roof window glazing, frames and junctions need to be considerably improved. However, the barriers to improving roof windows to levels above the current best standard practice remain great so long as we do not know the economic benefits of such improvements. The aim of this study was to quantify the scope for investing in improved roof window solutions in buildings insulated to consume nearly zero-energy. Based on two single-family houses in Copenhagen with typical roof windows and adequate daylighting, the study identified the prices at which various types of roof window improvements would have to be made available to achieve the same cost efficiency as improved insulation. If the improvements can be made available for less than these prices, the installation of improved roof windows would make it cheaper to construct well-lit and comfortable nearly zero-energy homes.

Dynamic solar shading is commonly suggested as a means of reducing the problem of overheating in well-insulated residential buildings, while at the same time letting daylight and solar irradiation in when needed. To critically investigate what dynamic shading can and cannot do compared to permanent alternatives in buildings with very low space-heating demand, this study mapped and compared energy, daylighting and thermal comfort for various combinations of window size and glazing properties, with and without dynamic shading. The study considered a loft room with sloped roof windows and moderate venting options in nearly zero-energy homes in Rome and Copenhagen. The more flexible solution space with dynamic shading made it possible to either reduce the time with operative temperatures exceeding the comfort limit by 40–50 h or increase daylighting by 750–1000 h more than could be achieved without shading. However, dynamic shading could not improve the optimum space-heating demand of the loft room in any predictable way, and without using dynamic shading, illuminances of 300 lx in 75% of the space could be achieved in 50–63% of the daylight hours with no more than 40–100 h exceeding the comfort ranges as defined by the Adaptive Thermal Comfort (ATC) model.

Occupancy is a key input variable for sizing heating, ventilation and air-conditioning (HVAC) in buildings. However, HVAC designers typically estimate occupancy data based on assumptions which rarely reflect the actual situation. Consequently, these assumptions might lead to under- or oversized HVAC systems that either provide too low or too high peak loads or ventilation airflows than actually required to satisfy indoor environmental quality (IEQ) requirements during building operation. To address these issues, existing studies suggest various methods for collecting and analysing occupancy, however mostly in single office spaces or at an overall building level. The objective of the present study was to evaluate the suitability of using passive-infrared (PIR) sensors mounted below occupants’ desks for collecting long-term occupancy data in open-plan and single office spaces. The method was tested in two office buildings for seven months. It determined occupant presence and count with an accuracy of 87.5% compared to manual observations. Furthermore, the study demonstrated that occupancy data could be used to (1) generate occupancy schedules for input in building simulation models, (2) potentially reduce design ventilation airflows for HVAC sizing and (3) evaluate decisions to change the office space layout (e.g. number of desks) for more efficient space-use.

Windows are central for the development of liveable nearly zero-energy homes and require careful consideration. Various studies have indicated that the effect of windows on energy consumption may change significantly with improved building insulation levels. Current guidelines on windows may therefore not apply in very well-insulated buildings, and more up-to-date information is needed about window solutions that are appropriate for the new conditions. This study maps the effect of multiple combinations of window size and basic glazing—and frame properties on energy, daylighting and thermal comfort in nearly zero-energy houses located in the European cities Rome and Copenhagen. The aim was to identify options that can support the easy and robust design of future homes with typical use of roof and facade windows. Hourly daylight levels were calculated in DAYSIM, while space heating demand and operative temperatures were calculated in EnergyPlus. The results support previous findings on the limited ability of nearly zero-energy buildings to utilise solar gains. It was found that U-values are becoming increasingly important for the energy performance of windows. The paper sketches the increased flexibility and related possibilities that may appear with improved roof window frame constructions and glazing U-values far lower than currently standard levels.

Heating, Ventilation and Air-Conditioning engineers face high demands from their clients to deliver reliable, optimized solutions that perform acceptably in terms of energy use and provided comfort. However, time and resources are scarce to deliver an optimized solution. To ensure that the solution works under most operation scenarios, the design is typically based on a combination of conservative rules-of-thumb, general guidelines and a large safety factor. The consequences are building service systems designed for operating conditions that never or very rarely occur leading to oversized systems. The objective of this paper was to propose a method for identifying oversized air-handling units with variable speed drives. It was demonstrated on a case study including six air-handling units in an office building. The method was able to determine that the air-handling units were not grossly oversized or undersized by comparing the measured airflow and SFP from the part- and full-load operation to the design airflow and SFP. However, the method should be extended to include additional performance criterion such as indoor climate and thermal efficiency to be able to conclusively confirm the size of the units.

This paper aims to document and analyse performance of a new design of diffuse ceiling ventilation system in a typical office room. A full scale measurement is carried out in a climate chamber with an office setup at the Technical University of Denmark. Indoor air temperatures, air speeds, wall surface temperatures, pressure loss of the ceiling and ventilation effectiveness are measured for an air change rate of 3.5 h−1 and 5.1 h−1 respectively. A computational fluid dynamics model of the office with the diffuse ceiling ventilation system is built and validated by the full scale measurement. The measurements of pressure loss across the ceiling show a low pressure drop between the plenum and the occupied zone. Ventilation effectiveness is measured to be close to 1 on average under the tested conditions. It is shown that the diffuse ceiling ventilation system is able to remove indoor pollutant in an efficient way. The draught risk is found to be insignificant by both experimental and theoretical investigations. A design chart based on “flow element” method is created for the diffuse ceiling ventilation system by calculations with the validated CFD model. The design chart serves as a guideline for design and dimension of the investigated diffuse ceiling terminals as an air distribution system.

An experimental study is reported in this paper for a diffuse ceiling ventilation concept. The analyses were carried out with two different porous surfaces mounted in a suspended ceiling: perforated tiles of aluminium and of gypsum. Ventilation air was supplied above the suspended ceiling effectively creating a plenum for air distribution. The experiments were carried out in a climatic chamber and documented an air change efficiency equal to fully mixed conditions with a pressure drop of 0.5–1.5 Pa and with no evidence of thermal discomfort. The magnitude of the pressure drop was enough to sustain the pressure of the plenum and ensure uni-directional airflow through the ceiling. Consequently only reverse flow of insignificant magnitude was observed which has a positive impact on the hygiene of the plenum. Furthermore, the measurements documented that the ceiling acts as a radiant cooling surface which increases the potential and applicability of the concept. Risk of thermal discomfort was not disclosed but the study did show evidence of large fluctuating air movements which could stem from transient behaviour creating sensations of draught to the occupants.

A core element in sustainable ventilation systems is the heat recovery system. Conventional heat recovery systems have a high pressure drop that acts as blockage to naturally driven airflow. The heat recovery system we propose here consists of two separated air-to-liquid heat exchangers interconnected by a liquid loop powered by a pump ideal as a component in a heat recovery system for passive ventilation systems. This paper describes the analytical framework and the experimental development of one exchanger in the liquid-loop. The exchanger was constructed from the 8 mm plastic tubing that is commonly used in water-based floor-heating systems. The pressure loss and temperature exchange efficiency was measured. For a design airflow rate of 560 L/s, the pressure loss was 0.37 Pa and the efficiency was 75.6%. The experimental results agree well with the literature or numerical fluid calculations. Within the analytical framework, the total heat recovery of two liquid-coupled exchangers was calculated to be in the range 64.5–75.4%, depending on the parasitic heat loss in the experimental setup. The total pressure drop of the heat recovery system is 0.74 Pa. Moreover, preliminary improvement calculations promise a future total efficiency of 80% with a pressure drop of 1.2 Pa.

Appropriate window solutions are decisive for the design of ‘nearly zero-energy’ buildings with healthy and comfortable indoor environment. This paper focuses on the relationship between size, orientation and glazing properties of facade windows for different side-lit room geometries in Danish ‘nearly zero-energy’ houses. The effect of these parameters on space heating demand, daylighting and thermal environment is evaluated by means of EnergyPlus and DAYSIM and presented in charts illustrating how combinations of design parameters with minimum space heating demand can be selected within a solution space defined by targets for daylighting and thermal comfort. In contrast with existing guidelines, the results show an upper limit for energy savings and utilisation of solar gains in south-oriented rooms. Instead, low U-values are needed in both north- and south oriented rooms before large window areas lead to reductions in space heating demand. Furthermore, windows in south-oriented rooms have to be carefully designed to prevent overheating. Design options for prevention of overheating, however, correspond well with options for low space heating demand. Glazings with solar control coating are therefore obvious alternatives to dynamic solar shadings. Regarding room geometry, deep or narrow south-oriented rooms show difficulties in reaching sufficient daylight levels without overheating.