Per Heiselberg

Aalborg University · Department of Civil Engineering

In the simulation of building overheating risks, the use of typical meteorological years (TMY) can greatly reduce the simulation workload and accurately reflect the distribution of simulation results according to the weather conditions over a given period. However, all meteorological parameters in most current TMY methods use a uniform weighting fa...

Nearly Zero Energy Building (NZEB) is becoming a standard for new and renovated buildings throughout the European Union (EU). Through the ongoing implementation of directives related to energy efficiency and NZEB-compliant buildings, the EU commission has established that new and renovated NZEB-compliant buildings shall be implemented cost-effectiv...

The concept 'Resilience' has gained wide international attention by experts and is now seen as the future target for the design of buildings. However, before using the word 'resilience', we must understand the semantics of the word. Resilience is not 'resistance' and is not 'robustness and is not 'sustainability', it is a more complex definition. A...

As the AIVC was created in 1979, the 40th anniversary of the AIVC was celebrated in October 2019 at the 40th AIVC conference in Ghent. In the context of this celebration, it was decided to publish 2 overview publications: An AIVC technote, which focuses on the overall history of the AIVC and those involved in the organisation (TN 69: 40 years to bu...

IEA EBC Annex 80 - Dynamic simulation guideline for the performance testing of resilient cooling strategies

The global effects of climate change will increase the frequency and intensity of extreme events such as heatwaves and power outages, which have consequences for buildings and their cooling systems. Buildings and their cooling systems should be designed and operated to be resilient under such events to protect occupants from potentially dangerous i...

There is little specific knowledge of actual temperature conditions in buildings. This paper contributes with results from a detailed long-term monitoring campaign of temperature conditions in 17 households. Furthermore, these measurements are combined with qualitative interviews with 22 occupants in 16 households, on their heating practices. Impli...

Radiant cooling is a promising thermal control technology for built environment. Unfortunately, condensation limits the potential of radiant cooling. Recently, numerous technologies have been developed to address the issue of condensation on radiant cooling surfaces. Nevertheless, a special review on the condensation control for radiant cooling is...

Accurate convective heat transfer coefficient (CHTC) is crucial to assess the night ventilation performance accurately. Previous experimental studies proposed CHTC correlations tailored for night cooling with diffuse ceiling ventilation (DCV) and mixing ventilation (MV). A holistic approach integrating the building energy simulation and optimizatio...

This chapter introduces the book’s contents and its structure. It also includes a short description of why Ventilative Cooling (VC) is increasing in importance in a scenario where building cooling needs are growing. The building sector is responsible for about 40% of primary energy consumption; space heating, cooling and ventilation have proved to...

This chapter introduces the main principles of ventilative cooling and the key performance indicators (KPI) to evaluate performance. It also presents and discusses the application potential and limitations as well as includes a critical discussion of barriers to ventilative cooling usage. The chapter is based on the outcome of the international res...

Recent European environmental directives, the prevalent consumer desire to minimize electricity costs, and the grid-driven need for flexible buildings all lead to a common outcome: the smart sustainable building (SSB). Coordinated by their building energy management systems (BEMS), SSBs steer their operation towards monetary gains for their owners,...

In Europe, one of the most sustainable solutions to supply heat to buildings is district heating. It has good acceptance in the Northern countries, a low-carbon footprint, and can easily integrate intermittent renewable energy sources when coupled to the electrical grid. Even though district heating is seen as a vital element for a sustainable futu...

Reaching environmental targets set by the European Union (EU) requires a constant renovation of the existing building stock to nearly Zero Energy Buildings (NZEB) in a cost-optimal manner. Studies show that the renovation rate of the existing building stock is more than two times less than what is necessary to reach the targets. Furthermore, the ma...

The concept of climate resilience has gained extensive international attention during the last few years and is now seen as the future target for building cooling design. However, before being fully implemented in building design, the concept requires a clear and consistent definition and a commonly agreed framework of key concepts. The most critic...

Increasing envelope facet albedos considerably reduces solar heat gain, thus yielding building cooling energy savings. Few studies have explored the potential benefits of utilizing cool coatings on building envelopes (“cool-coated buildings”) based on life-cycle cost analysis. A holistic approach integrating the field testing, building energy simul...

The convective heat transfer coefficient (CHTC) is a crucial parameter for night ventilation performance estimation. This paper investigates the heat transfer of night ventilation with diffuse ceiling ventilation (DCV) concept in an office room. A series of dynamic full-scale experiments were conducted with different thermal mass distribution schem...

The convective heat transfer coefficient (CHTC) is a crucial parameter for night ventilation performance estimation. This paper investigates the heat transfer of night ventilation with diffuse ceiling ventilation (DCV) concept in an office room. A series of dynamic full-scale experiments were conducted with different thermal mass distribution schem...

The purpose of night ventilation (NV) is to improve building energy and thermal comfort performance. The key to accurately predicting NV performance is selecting the appropriate convective heat transfer coefficient (CHTC) at different surfaces of the built environment. The current CHTC correlations used in building energy simulation tools are limit...

As part of the EBC Annex 80 - Resilient cooling of buildings activities, the Thermal Condition Taskforce was created, in April 2020. In coordination with all other groups and the Weather Data Taskforce, two objectives were set by the Annex leader Dr. Peter Holzer. Firstly, to define common thermal conditions to assess different cooling technologies...

This book includes the most recent outcomes from research and professional practice in the ventilative cooling field, gathered by the selected panel of authors. It provides essential contents to face and reduce the rise of space cooling and ventilation energy uses in buildings by alternative ventilation and cooling solutions. The book is organised...

This paper proposes a new bi-objective optimization model, trading-off cost and environmental impacts, for sizing the key electrical and thermal devices in a zero energy building (ZEB), i.e. a building that roughly generates as much renewable energy as it consumes annually. A salient novel feature is the consideration of the environmental impacts,...

The important focus of the energy strategy of the European Union relies on the concept of zero energy building, which is, by definition, a building that roughly produces yearly as much renewable energy as it consumes. This paper proposes an enhanced mixed-integer nonlinear programming model for optimal sizing of photovoltaic and battery energy stor...

The rising cooling demand and overheating in the building sector, especially in office buildings, have intensified research interest in recent years. Night ventilation (NV) as a passive energy technology has shown a great potential cooling energy and ameliorate indoor thermal environment. In this paper, a holistic approach involving global sensitiv...

A ventilated window system enhanced by phase change material (PCM) has been developed, and its energy-saving potential examined in previous works. In this paper, the ventilation control strategies are further developed, to improve the energy-saving potential of the PCM energy storage. The influence of ventilation airflow rate on the energy-saving p...

Renovation of existing buildings is an indispensable part of achieving European efficiency and environmental targets. This paper applies different assessment methodologies to find optimal renovation, given different evaluation criteria. The performed literature study identifies the cost-optimal methodology employing Life Cycle Cost (LCC) calculatio...

Radiant heating and cooling (RHC) systems typically work together with ventilation systems in order to take care of sensible loads, latent loads and pollutants. There are various combinations according to the location of radiant surfaces and air distribution principles. Even though there are extensive researches on radiant systems and ventilation s...

This paper aims to visualize how the planned electrification of heat demand together with the utilization of energy flexibility in buildings will influence the performance of local electricity network. Thereby, the work contributes to the research on smart energy system in the residential sector. The flexibility service is provided by two demand-si...

What is the difference between the thermal sensation and skin temperature in transitional spaces with or without air-conditioning? Is it necessary to have intensive air-conditioning in transitional spaces of southern China? In order to answer these questions, this paper presents a comparative study performed in a selected shopping mall with two tra...

This study proposes a PCM enhanced ventilated window (PCMVW) system for ventilation preheating/precooling purposes for building energy conservation. It is designed into a summer night cooling application and a winter solar energy storage application using different control strategies. An EnergyPlus model of the PCMVW is built to investigate the con...

This paper presents a phase change material enhanced ventilated window (PCMVW) for both ventilation pre-cooling and pre-heating purposes. The PCM heat exchanger is used as a heat sink in the ventilation pre-cooling application and thermal energy storage in the ventilation pre-heating application. The paper presents a night cooling experiment and a...

Evolution of energy standards led to high-performance buildings requiring very low energy for their operation. Occupancy is the variable with the greatest impact on nearly Zero Energy Building (nZEB) energy performance because both constructive and technical characteristics have been improved over time. Occupants influence energy use in buildings a...

District heating has been found to be a key component of future and reliable smart energy grids comprising 100% of renewable energy sources for countries with dominant heating season. However, these systems face challenges that require a deeper understanding of the coupling between the distribution networks and the connected buildings, to enable de...

As energy standards focus on reducing energy use in new buildings, attention is drawn to the gap between the expected and actual building operation and energy performance. This performance gap can be associated with the building construction, its systems, its unbalanced operation, the assumptions on occupancy profiles during the design phase, or th...

Intermittent energy resources challenge the ways in which the existing energy system operates. Studies suggest that residential buildings can provide a flexibility service for district heating (DH) systems. This technique involves load shifting by heating buildings to higher temperatures at times when energy is more readily available, thus diminish...

Overheating in buildings during summertime, especially in office buildings is emerging as a challenge. Night mechanical ventilation (NMV) seems to be an energy-efficient technique by inducing the cold ambient air with a fan to cool the exposed building thermal mass and save air-conditioner energy for the following day. However, as sufficient coolin...

Low energy buildings are highly insulated and airtight and therefore subject to overheating risks, where Ventilative cooling (VC) might be a relevant solution. VC is an application (distribution in time and space) of air flow rates to reduce cooling loads in spaces using outside air driven by natural, mechanical or hybrid ventilation strategies. Ve...

Intermittent energy resources challenge the ways in which the existing energy system operates. Studies suggest that residential buildings can provide a flexibility service for district heating (DH) systems. This technique involves load shifting by heating buildings to higher temperatures at times when energy is more readily available, thus diminish...

Increasing roof albedo (using a “cool” roof) and night ventilation are passive cooling technologies that can reduce the cooling loads in buildings, but existing studies have not comprehensively explored the potential benefits of integrating these two technologies. This study combines an experiment in the summer and transition seasons with an annual...

The main goal of the ENOVHEAT project is to develop, build and test a prototype of an innovative heat pump based on active magnetic regenerator technology. This device can be coupled to a ground source heat exchanger and an under-floor heating system to provide for the space heating needs of a low-energy house in Denmark. However, the use of a simp...

Overheating and energy-extensive consumption in buildings, especially in office buildings, are emerging challenges. Night ventilation (NV) is a promising technique. The performance of NV can be evaluated by a series of performance indicators. As many design parameters affect those indicators, it is beneficial to choose suitable indicators and ident...

This article presents a PCM solar air heat exchanger integrated into ventilated window developed to maximize the use of the solar energy to pre-heat the ventilated air. The system is designed to improve the indoor air quality and thermal comfort by continuous pre-heated air supply at a reduced energy use through the capturing and storing of solar e...

The work presented in this paper is developed as a part of the Horizon 2020 EU project REFURB. The number of deep energy retrofits is falling behind the EU ambitious targets. The REFURB project aims at finding technical and nontechnical solutions that match the demand and supply side of the residential building renovation market. Due to the multipl...

The objective of this study is to investigate and assess the energy flexibility performance of typical Danish office buildings constructed at different periods. Four building study cases have been compared with different heating demands, structural thermal masses, envelope insulation levels and infiltration rates. All cases are equipped with the sa...

The significant expansion of intermittent renewable energy sources can compromise the stability of energy grids due to the mismatch between instantaneous energy use and production. Buildings have a large potential for energy storage and demand-side management, which can offer energy flexibility to a Smart Grid system. Smart control of heating, vent...

During recent years, the research in reduction of energy use in buildings has focused primarily on decrease of space heating needs, energy for ventilation and recently cooling, whereas domestic hot water (DHW) has been overlooked. In 2013, the energy use for DHW was estimated at 16% of total heat requirement in EU28 households, but in new energy-ef...

Prosumers have a different interaction with the distribution network in comparison with traditional consumers. They have a bi-directional power exchange with the grid, meaning they receive from as well as deliver electricity to the network. The emergence of prosumers is expected to challenge the way network operators control the residential low-vol...

Roof windows are widely used in northern European countries, contributing positively by giving daylight, passive solar heat and view to the outside. In order to improve their thermal property, triple glazing unit together with external shutter are more and more common on the market. Additionally, the junction part between window and roof is also im...

This article presents the results of a numerical study investigating the influence of the main building parameters on the indoor space heating energy flexibility of a Danish house. The focus is placed here on the envelope insulation level, the structural thermal mass, the additional thermal mass of indoor content (indoor items/furniture, PCM integr...

The implementation of energy flexibility using thermal storage of building structure is one of the key solutions for buildings in contributing to a stable exploitation and distribution of renewable energy. The objective of this study is to investigate the performance of energy flexibility of a nearly zero-energy building with weather predictive con...

In Hot Summer and Cold Winter Climate Zone, the cooling potential of natural/passive night ventilation is limited during summer due to the insignificant difference between the outdoor and indoor temperatures. Therefore, a novel mechanical ventilation strategy, the wall-mounted attached ventilation (WAV) system, is proposed in the present paper to i...

This paper proposes a ventilated window with a phase change material (PCM) heat exchanger as a new window application. In summer, night ventilation mode is operated to discharge energy stored in PCM by the ambient cold air, which can be reloaded again, when ventilation pre-cooled air is provided. Numerical model is built and verified by full-scale...

Building regulations are important policy instruments for increasing building energy efficiency. However, when it comes to actual energy use, studies have shown that improvements in building energy efficiency are offset by changes in the inhabitants’ comfort practices. Nevertheless, the improvement of energy efficiency continues to be a cornerstone...

The EnovHeat project aims at developing an innovative heat pump system based on the magnetocaloric effect and active magnetic regenerator technology to provide for the heating needs of a single family house in Denmark. Unlike vapor-compression devices, magnetocaloric heat pumps use the reversible magnetocaloric effect of a solid refrigerant to buil...

The ventilative cooling potential tool (VC tool) aims at assessing the potential effectiveness of ventilative cooling strategies by taking into account also building envelope thermal properties, occupancy patterns, internal gains and ventilation needs. The analysis is based on a single-zone thermal model applied to user-input climatic data on hourl...

The study in this article investigates 15 ventilated window typologies with different pane configurations and glazing types in climates of four European countries (United Kingdom, Denmark, France and Germany) in order to identify the optimum typology with regard to their energy balance and impact on thermal comfort. Hourly simulations of the heat b...

The use of solar shading in future low energy office buildings is essential for minimizing energy consumption for building services, while maintaining thermal conditions. Implementing solar shading technologies in energy calculations and thermal building simulation programs is essential in order to demonstrate the effect of adaptive solar shading....

Many numerical models for building energy simulation assume empty rooms and do not account for the indoor content of occupied buildings. Furnishing elements and indoor items have complicated shapes and are made of various materials. Therefore, most of the people prefer to ignore them. However, this simplification can be problematic for accurate cal...

Automated window opening control systems with integrated ventilative cooling strategies may significantly diminish the thermal discomfort and overheating risk of dwellings during cooling periods in temperate climates. One of the challenges with demonstrating the benefits of the systems is the lack of building performance simulation (BPS) tools whic...

The increasing share of intermittent renewable energy on the grid encourages researchers to develop demand-side management strategies. Passive heat storage in the indoor space is a promising solution to improve the building energy flexibility. It relies on an accurate control of the transient building temperature. However, many of the current numer...

In the coming years, the European building sector faces a large challenge in reducing the energy consumption and CO2 emission. To reach these targets private homeowners must participate by renovating their buildings, but various barriers prevent them from conducting extensive energy renovations. Studies have, nonetheless, shown that improvements in...

Diffuse ceiling ventilation (DCV) is a novel air distribution system that utilises the suspended ceiling as diffuser for inlet air. The performance and system characteristics have, so far, mainly been tested in laboratory experiments and numerical simulations yielding good results in terms of occupant comfort at high ventilation rates. To supplemen...

Stakeholders, researchers and designers apply different overheating metrics because they follow different comfort theories or comply with different regulations and standards. As a result, there is no common ground for generalization, intercomparison and final concordance of their conclusions. Correlation of indices would simplify the analysis being...

Major and deep energy renovations on residential buildings are expected in Europe over the next several years. The current developments towards nearly-zero energy houses in building efficiency have increased the overheating occurrences indoors. For house users summer thermal discomfort is an unknown challenge that they have not faced in the past. T...

Diffuse ceiling ventilation is an innovative ventilation concept where the suspended ceiling serves as an air diffuser to supply fresh air into the room. Due to the large opening area, air is delivered to the room with very low velocity and no fixed direction, therefore the name ‘diffuse’. Compared with conventional ventilation systems (mixing or d...

A novel system combining diffuse ceiling ventilation and radiant ceiling was proposed recently, with the aim of providing energy efficient and comfort environment to office buildings. Designing of such a system is challenging because of complex interactions between the two subsystems and a large number of design parameters encountered in practice....

The objective of this study is to assess the potential of buildings to modulate the heating power and define simple control strategies to exploit the flexibility potential considering both energy and thermal comfort. Two residential buildings with different levels of insulation and air-tightness have been modelled. This wide range of thermal proper...

In Denmark, around Europe and in the rest of the world there is a challenge of motivating homeowners to conduct private energy renovations despite a number of benefits. A particular great energy saving potential is present in the Danish single-family houses erected in 1960–1979, but the potential is not utilized for various reasons. However, survey...

This paper investigates the dynamic cooling performance of a novel system combining natural ventilation with diffuse ceiling inlet and thermally activated building systems (TABS). This system is tested in the lab under three climatic conditions representing typical seasons in Denmark, including a typical winter day, a typical day in the transitiona...

The objective is to present a high-resolution model of household electricity use developed based upon a combination of measured and statistical data. It is a bottom-up model, which uses the 1-min cycle power use characteristics of a single appliance as the main building block. The effect of parameters, such as the number of occupants and their atti...

The objective of the present study was to develop a solar shading control strategy for venetian blinds applied on office buildings in cold climates in order to achieve acceptable energy use and indoor environmental performance. A control strategy based on a combination of internal and external shading develop within the Norwegian R&D project “Fasad...

Many post-occupancy comfort studies of energy renovated residential buildings have documented elevated temperatures above comfort levels, not only during the summer period but also during the shoulder months. The main focus in renovation projects is on heat savings while the risk of overheating is not considered. This paper analyze in which situati...