Abstract

Efficient energy recovery from used air with the goal of reducing energy use is important for realizing low energy houses. Rotary heat exchangers are very energy efficient, but have the drawback of transferring odours from exhaust air to fresh supply air. To avoid this, flat plate heat exchangers are commonly used where odour transfer might cause problems. Nevertheless, these may not properly handle water condensation and frost formation at low outdoor temperatures. The so-called membrane-based energy exchangers are an alternative to the flat plate heat exchanger. In a membrane-based exchanger, moisture is transferred from the humid exhaust air to the dry supply air avoiding condensation at the exhaust airside. In this work, a membrane energy exchanger was compared to a thin non-vapour permeable plastic foil heat exchanger. The study focused on verifying condensation and freezing problems and evaluating the performance of the membrane energy exchanger. The experiments showed that non-permeable heat exchangers have problems with condensation and freezing under test conditions. Under the same conditions, the membrane-based exchanger did not experience the same problems. However, additional problems with swelling of the membrane in high humidity conditions showed that the tested membrane type had drawbacks and needs further development to become commercially applicable.

Abstract

Efficient energy recovery from used air with the goal of reducing energy use is important for realizing low energy houses. Rotary heat exchangers are very energy efficient, but have the drawback of transferring odours from exhaust air to fresh supply air. To avoid this, flat plate heat exchangers are commonly used where odour transfer might cause problems. Nevertheless, these may not properly handle water condensation and frost formation at low outdoor temperatures. The so-called membrane-based energy exchangers are an alternative to the flat plate heat exchanger. In a membrane-based exchanger, moisture is transferred from the humid exhaust air to the dry supply air avoiding condensation at the exhaust airside. In this work, a membrane energy exchanger was compared to a thin non-vapour permeable plastic foil heat exchanger. The study focused on verifying condensation and freezing problems and evaluating the performance of the membrane energy exchanger. The experiments showed that non-permeable heat exchangers have problems with condensation and freezing under test conditions. Under the same conditions, the membrane-based exchanger did not experience the same problems. However, additional problems with swelling of the membrane in high humidity conditions showed that the tested membrane type had drawbacks and needs further development to become commercially applicable.

Abstract

A frost-free membrane energy exchanger design model is developed combining the conventional ε−NTU method with a frost limit model. A concept of plate performance index is defined to evaluate the net energy saving ability. The frost-free design model and plate performance index are employed for a case study of single-family dwelling with an all-fresh-air air handling unit with a heat/energy recovery exchanger. The membrane energy exchanger, which is able to ensure frost-free operation without extra frost control strategies, is applicable to most cold climates for residential applications. The membrane energy exchanger has a significant energy saving potential compared to conventional plate heat exchangers. Preheating rather than enlarging the energy transfer area is recommended for severe cold climates.

Abstract

New buildings have to satisfy ever-tightening standards regarding energy efficiency and consumption. This results in higher insulation levels and lower air leakages that reduce heating demands. However, even at moderate outdoor temperatures these buildings are easily warmed up to such a degree that in order to ensure acceptable indoor environment quality, removal of excess heat becomes unavoidable. Use of electric energy related to mechanical cooling is considered incompatible with achieving zero energy buildings (ZEB). The use of ventilative cooling (VC) in combination with mechanical cooling means energy consumption reduction due to lower use of mechanical ventilation and cooling system.
This paper examines the application of ventilative cooling solutions in cold climates through simulations of an existing detached single family house in Norway, the ZEB Living Lab at NTNU/SINTEF. The house has computer controlled motorized windows. This will enable natural ventilation in some part of the year and could then reduce the energy use of fan power. The openable window are placed at the north and south facades and this enables considerably cross ventilation and also stack ventilation as some windows are placed four meters high.
IDA ICE program will be used to calculate the energy consumption of the baseline simulation: demand controlled ventilation with variable air volume and mechanical cooling. By means of using CONTAMW the airflow profiles while using controlled window opening are calculated and used as input profiles in IDA ICE to calculate the energy consumption while using hybrid mode ventilation.
Results show significant energy savings when using ventilative cooling. Due to the low outdoor temperatures in Norway the use of ventilative cooling remove mechanical cooling demands almost completely. The reference for comparison has been the European standard EN15251 (class II).
Ventilative cooling is proven to be relevant in combination with mechanical ventilation and will be crucial to achieving energy targets for new zero energy buildings while the indoor climate is maintained.

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

In Norway, a large portion of the building stock originates from the period from 1955 to 1990. Many of these buildings fail to comply with the current building regulations regarding the energy consumption. In this study, the possibility for upgrading a hypothetical apartment building with an oil-based heating system has been investigated employing simulations from the IDA Indoor Climate and Energy software. For the construction of the original building, customs and regulations from the period 1981-90 were employed, and the building envelope was upgraded to the requirements of the Norwegian research centre on Zero Emission Buildings. Two alternative heating systems have been investigated: solar thermal collectors (i) alone and (ii) as combined with borehole thermal storage and a ground-source heat pump. For each case, the energy consumption, thermal comfort and indoor climate were studied. The simulations predict a reduction in the total annual heat demand to one third of the original with the upgrading. For the alternative heating systems, with solar collectors alone the demand for additional electric heating was still considerable, however in the combined system it was negligible. Regarding thermal comfort, in the upgraded building longer periods with elevated temperatures were observed.

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.

Abstract

Reduced energy consumption is one of the most cost effective ways of reducing CO₂ emissions for combustion of fossil fuels. Residential buildings must become more energy efficient according to the Energy Performance in Buildings Directive (EPBD). The demands for domestic hot water have become more significant. Therefore the share of domestic hot water (DHW) in high insulated houses constitutes an increasing share of total heating demand.

For DHW and space heating purpose CO₂ tripartite gas cooler heat pumps are among the most efficient systems. Due to heat rejection at different temperature levels a large enthalpy difference and low compressor power input is achieved. A dynamic  model for a CO₂ heat pump system combined with energy storage (by means of ice) for a zero emission building (ZEB) has been developed. The goal of the simulation is the optimization of the heat pump and of its operational modes.