Mechanical Ventilation With Heat Recovery Research Articles

A review of the indoor air quality in residential Passive House dwellings

The Passive House (PH) Standard is a voluntary building energy performance standard focused upon reducing space heating demand to a very low level and therefore considered a viable climate change mitigation technology. Besides comfort and energy requirements, the PH standard also defines criteria with respect to ventilation. However, the question remains, how well do PH dwellings perform when they are occupied? Does the PH approach provide good indoor air quality (IAQ) for its occupants and how does IAQ compare to non-PH homes, in particular, naturally ventilated homes? Additionally, can PH certification improve the quality of installed ventilation systems? This paper summarizes indoor air quality relevant aspects of the PH standard and presents results from measurements examining in-use IAQ in more than 600 PH or PH-like, newly built or retrofitted dwellings. The results reveal that pollutant and carbon dioxide concentration are generally lower compared to naturally ventilated homes, presumably due to the requirement to install a balanced Mechanical Ventilation with Heat Recovery (MVHR) system. Results also suggest that the quality assurance measures of PH certification are capable of improving ventilation and IAQ performance. However, the lack of cooking fume capture requirements in the PH standard, in combination with efforts to avoid energy losses associated with a possible extraction kitchen hood, may lead to elevated particulate matter concentration in PHs. Future research on cooking induced IAQ impairment is encouraged to assess the effectiveness of recently published PH-specific recommendations. Future efforts in empirical IAQ research should also address the lack of high quality IAQ measurement data and the standardisation of IAQ assessment methods and protocols.

Applying Spanish Acoustic Regulations to mechanical ventilation with heat recovery systems. Case study.

Due to recent changes in IAQ (Indoor Air Quality) and energy efficiency requirements, MVHR (Mechanical Ventilation with Heat Recovery) has become increasingly common in Spanish new build dwellings. Regarding acoustics, Spanish Decree RD 1367/2007 sets out limits for sound pressure levels due to building services and describes the noise measurement and assessment procedure, which applies also to ventilation noise. The assessment procedure consists of a series of measurements of different noise parameters and then the calculation of corrections due to tonal, low frequency and impulsive components. This paper shows an example of a MVHR fan unit installed in the ceiling of a common dwelling, where some measurements were performed. Based on these measurements, this paper discusses the noise measurement and assessment procedures and proposes some improvements for the Spanish acoustic regulations. In addition, it also analyses the available calculation methods (ASHRAE and VDI 2081) and their application to comply with Spanish requirements.

Noise from ventilation systems in dwellings - Regulations and field test procedures in selected countries in Europe

In most countries in Europe, regulatory noise limits apply for service equipment in housing. During the last few decades, mechanical ventilation with heat recovery (MVHR) has become increasingly prevalent in new and retrofitted housing in Europe. The MVHR systems supply fresh air to obtain good indoor air quality, with minimal heat losses. However, the systems may operate continuously 24 hours/day and transmit noise into and between rooms by many possible paths. In practice, many people get annoyed or disturbed by the noise, especially during nighttime or when having quiet activities. Some countries have lower service equipment noise limits for continuous sources than for non-continuous sources, and lower limits also apply for the upper quality classes in acoustic classification schemes. Thus, both design and measurements become challenging. The aim of this paper is to investigate the noise limit values and descriptors applied to ventilation systems in housing in selected countries in Europe and compare limit values, field test and rating procedures as well as operating conditions and enforcement related to the limit values. Indications of typical design methods will also be included.

Investigating the potential energy savings of MVHR in automotive HVAC systems

The environmental impact of ICEVs (internal combustion engine vehicles) have led to increasing numbers of EVs (electric vehicles) and plug-in hybrid vehicles being developed. However, current HVAC (heating, ventilation and air conditioning) systems can heavily impact energy consumption, reducing EV range. MVHR (mechanical ventilation with heat recovery) is an approach to minimise the HVAC energy consumption currently used in buildings to meet the Passivhaus building standard and can be used for both heating and cooling. In this work a MATLAB Simulink model and a road load model are used to quantify potential energy reduction and corresponding range savings from an automotive MVHR HVAC system. The model is calibrated against data from the industry sponsor for a baseline non-MVHR vehicle. The results show a 74.3%–94.9% HVAC energy consumption and corresponding range savings of a mean average of 8.8%–11.0% range savings over the baseline case without MVHR, and a corresponding 0.5%–2.5% range increase over the industry sponsor’s vehicle’s range under certification conditions. The work concludes that the application of MVHR technology to automotive cases is beneficial.

Efficacy of coupling heat recovery ventilation and fan coil systems in improving the indoor air quality and thermal comfort condition

Mechanical Ventilation with Heat Recovery (MVHR) systems are gaining increasing interest in buildings with low energy demand, for improvement of the Indoor Air Quality (IAQ) and reduction of the ventilation energy loss. In retrofitted buildings, MVHRs are often integrated with an additional air heater to cover space heating demand. Hence, evaluation of the interactions between MVHR and heat emitter, and their effects on indoor airflow characteristics is of significant importance. The present study aims to investigate effects of a combined MVHR-fan-coil system in heating mode on IAQ and thermal comfort parameters inside a retrofitted room, by means of a computational fluid dynamic (CFD) code. The proposed CFD model is validated by comparing the numerical results with experimental data. The results yielded by numerical simulations allow evaluating the indoor environmental quality characteristics as well as addressing the MVHR and fan coil interactions. The results indicate that the airflow discharged from the fan coil could have a significant impact on the age of the air; while it provides a desirable thermal comfort condition within the room, it may hinder to some extent delivery of the fresh air to the occupied zone due to creation of counterflow fields. Furthermore, it is shown that although increasing the fan speed (ON mode) would slightly enhance the air change efficiency, the OFF mode yields not only a better distribution of the fresh air but also a higher ventilation efficiency than when fan coil operates.

An Investigation into Indoor Radon Concentrations in Certified Passive House Homes.

The Energy Performance of Buildings Directive (EPBD) has introduced the concept of Nearly Zero Energy Buildings (NZEB) specifying that by 31 December 2020 all new buildings must meet the nearly zero- energy standard, the Passive House standard has emerged as a key enabler for the Nearly Zero Energy Building standard. The combination of Passive House with renewables represents a suitable solution to move to low/zero carbon. The hypothesis in this study is that a certified passive house building with high levels of airtightness with a balanced mechanical ventilation with heat recovery (MVHR) should yield lower indoor radon concentrations. This article presents results and analysis of measured radon levels in a total of 97 certified passive house dwellings using CR-393 alpha track diffusion radon gas detectors. The results support the hypothesis that certified passive house buildings present lower radon levels. A striking observation to emerge from the data shows a difference in radon distribution between upstairs and downstairs when compared against regular housing. The study is a first for Ireland and the United Kingdom and it has relevance to a much wider context with the significant growth of the passive house standard globally.

Frost reduction in mechanical balanced ventilation by efficient means of preheating cold supply air

This study has focused on evaluating the financial potential of wastewater and geothermal heat recovery systems in a multi-family building. The recovered heat was used to improve the performance of mechanical ventilation with heat recovery (MVHR) system during the coldest days in central Sweden. The main issue, which was targeted with these solutions, was to reduce frost formation in the system and hence increase its thermal efficiency. By looking at the life cycle cost over a lifespan of 20 years, the observed systems were being evaluated economically. Furthermore, statistical analyses were carried-out to counter the uncertainty that comes with the calculation. It was found that the studied wastewater systems have a high possibility of generating savings in this period, while the one fed by geothermal energy is less likely to compensate for its high initial cost. All designed systems however, managed to reduce operational cost by 35-45% due to lower energy usage.

Reducing the defrosting needs of air-handling units by using heat from wastewater in apartment buildings in cold climates

This paper is the second part of a two-part series that investigates the energy-saving potentials of a novel wastewater heat recovery system connected to mechanical ventilation with heat recovery (MVHR). The main idea is to use the heat from stored wastewater to preheat the incoming cold outdoor airflow to the MVHR and thereby reduce the defrosting needs of the MVHR. The study evaluated the potential of two air preheaters, AP0.4 m x 0.4 m x 0.4 m and AP0.8 m x 0.8 m x 0.4 m, placed in front of the existing MVHR. Dynamic simulations in this study have shown that the smaller air preheater could lower the frost threshold temperature by 5 °C and the larger one could reduce it by 11 °C. Without an air preheater, the defrosting was needed during nearly two-thirds of January in the studied climate. By contrast, with the evaluated air preheaters in front of the MVHR, the defrosting was needed during 45% and 20% of the evaluation period, respectively. The results also showed that frost growth inside the heat exchanger could be reduced by 38% with AP0.4 m x 0.4 m x 0.4 m and by 62% with AP0.8 m x 0.8 m x 0.4 m during the peak load. The main conclusion is that the suggested heat recovery system has good potential for improving the overall performance of MVHR systems in cold climates.

Maximizing thermal performance of building ventilation using geothermal and wastewater heat

An efficient use of waste heat recovery and geothermal heat can play an important role in lowering the overall energy use of buildings. This study evaluated the potential of geothermal energy and heat recovery from residential wastewater to reduce the energy need of building-ventilation in cold climates. The performance of the mechanical ventilation with heat recovery (MVHR) system in a multi-family building located in central Sweden was studied. The focus of the investigation was on reduction of frosting in the air handling unit during the coldest months. Three configurations of one air preheating system fed by two renewable heat sources, wastewater and geothermal energy, were studied. It was found that compared to building without an air preheating system, the suggested air preheating systems reduced the defrosting time to 25%. By controlling and maintaining the preheated air temperature to slightly above the defrosting start, air heat recovery efficiency of MVHR above 80% was achieved for 90% of the studied time during heating season when frosting occurs. The energy need for the circulation pumps in the suggested air preheating systems was 5% of the recovered thermal energy from wastewater. The simulation results suggested that the air preheating system using wastewater heat recovery with a temperature-stratified storage tank was the most efficient one among the studied systems.

Energy and defrosting contributions of preheating cold supply air in buildings with balanced ventilation

Residential wastewater is a constant and available source for saving energy. This paper mainly investigated the possibility of utilizing wastewater heat to reduce ventilation heat load. Swedish residential buildings are to a significant extent served by mechanical ventilation with heat recovery (MVHR) systems. MVHR in airtight buildings has greatly reduced ventilation heat loads, especially in cold climate countries such as Sweden. However, cold outdoor air might lead to frost formation in heat recovery exchangers which increases the energy use. Therefore, this study focused on reducing the defrosting need by preheating the incoming cold outdoor air to MVHR during the coldest days. The effects of preheating the incoming air to MVHR on ventilation heat load and annual ventilation heating demand were also studied. It was found that the heat recovery efficiency of MVHR is the most decisive factor in rating the performance of the combined system with an air preheater. Contributions of the studied air preheater to annual energy savings were negligible. On the other hand, the reduction of the initial defrosting need was significant. The obtained results showed that the defrosting need in a building located in central Sweden in two cases of an MVHR system equipped with a rotary heat exchanger/plate heat exchanger was eliminated/reduced to one-third. The defrosting need was reduced by 50% in northern Sweden for both cases.

Stressing the passive behavior of a Passivhaus: An evidence-based scenario analysis for a Mediterranean case study

This paper first reports the outcomes of a one-year measurement campaign of a passive house built in the Mediterranean climate of Cesena (Italy) in terms of thermal comfort parameters temperature and relative humidity and Indoor Environmental Quality (IEQ) parameter CO2 concentrations. The design carried out with the help of the steady state Passive House Planning Package (PHPP) was able to guarantee good comfort conditions during the heating period, but on the other hand, overheating occurrences during the cooling season have been recorded for almost 50% time according to EN 15251 Standard. Further analyses conducted with the help of dynamic simulations in EnergyPlus allowed identifying the insulation levels and ventilation mode as the key design factors to change in order to reduce overheating to less than 20% of time while keeping a comfortable indoor environment in winter.The simplifications that can be made by reducing the insulation material thickness (up to a third of the original value) on the roof and on the walls, replacing triple-glazed windows with double-glazed windows and implementing a hybrid ventilation strategy instead of using Mechanical Ventilation with Heat Recovery (MVHR) alone could also lead to economic savings. These savings, due to both lower construction costs and operational energy savings, amount to 8755 euros in terms of Net Present Value (NPV) over 30 years' time.The Passivhaus Standard can still be regarded as a good reference for designing low-energy and comfortable houses in a Mediterranean climate if some simplifications are made according to detailed building performance simulations.

Evaluating the potential of reducing peak heating load of a multi-family house using novel heat recovery system

The current study evaluated the potential of reducing ventilation heat load by using heat from waste water in mechanical ventilation with heat recovery (MVHR) served Swedish residential buildings. A typical Swedish low-energy, multi-family house locating at the northern part of Sweden was selected to present the analysis. The building was locating at the northern part of Sweden and was served by mechanical ventilation with heat recovery (MVHR). The data from on-site measurements and analytical model were applied to evaluate the reduction potential of the suggested heat recovery system. The study focused on the evaluation of benefit of using an air preheater in front of the existing MVHR system. Two different sizes of an air preheater design: Small air preheater with the size of 0.4 m × 0.4 m × 0.4 m (AP0.4m×0.4m×0.4m), feed with waste water flow of 0.15 kg/s (from storage tank to air preheater); and a large air preheater with the size of 0.8 m × 0.8 m × 0.4 m (AP0.8m×0.8m×0.4m), feed with waste water flow of 0.2 kg/s. It was found that the heat recovery efficiency of MVHR is the core to determine the selection of air preheaters. In comparison to the MVHR without air preheater, maximum air supply temperature improvements of 25% and 41% were found from AP0.4m×0.4m×0.4m and AP0.8m×0.8m×0.4m, respectively. The studied system reached its highest contributions when the heat recovery efficiency of MVHR was between 80% and 85%. On average, AP0.4m×0.4m×0.4m can reduced the peak heat load up to 27%. AP0.8m×0.8m×0.4m can reduce the peak heat load up to 40% in the studied climate.

Meta-analysis of indoor temperatures in new-build housing

ABSTRACTDespite growing concerns about overheating, a lack of evidence exists on the scale of the problem, particularly in contemporary UK housing. This paper presents the results of a meta-analysis of indoor temperatures in selected low-energy housing. Temperature data recorded at five-minute intervals in 60 dwellings across 19 demonstration projects (2012–14) were collated and analysed to investigate the prevalence of overheating. Findings evidence high summertime temperatures, with 27% of living rooms exceeding 28°C during August. Based on the Chartered Institution of Building Services Engineers (CIBSE) threshold of 5% annual occupied hours > 25°C, 57% of bedrooms and 75% of living rooms were classified as having overheated. Overall, 30% of living rooms exceeded the adaptive comfort threshold of > 3% occupied hours ΔT ≥ 1 K. The results suggest a fundamental relationship between ventilation and indoor temperatures. The higher minimum and average summertime temperatures observed in mechanical ventilation with heat recovery (MVHR) homes (p < 0.05) and lower temperature range (p < 0.001) suggest the need for greater attention to adequate summertime ventilation provision in airtight homes. The results demonstrate a high prevalence of overheating in exemplary housing, indicating the need for greater efforts to ensure the effective implementation of strategies to minimize overheating and improve ventilation in low-energy homes.

On the oversupply of heat to bedrooms during winter in highly insulated dwellings with heat recovery ventilation

The study presented in this paper originated from observations made regarding the thermal conditions during winter in highly insulated dwellings with mechanical ventilation with heat recovery (MVHR). Previous observations indicate an oversupply of heat to bedrooms and a successive extensive window ventilation, which leads to an increased space-heating demand.Detailed simulations were conducted to explain the causes for the observed thermal conditions and to elaborate improved solutions for heating and ventilation during winter. Various MVHR solutions and control strategies, as well as building design solutions, were investigated regarding their impact on the thermal conditions in bedrooms and on the space-heating demand.The results clearly illustrates that the supply-air temperature and the temperatures in the living room and bathroom have substantial effects on the thermal conditions in the bedrooms. A one-zone MVHR solution, with approximately the same the supply-air temperature to all rooms, has clear limitations regarding the provision of thermal comfort in bedrooms.The clear potential of a two-zone MVHR solution, where the supply-air temperature to the bedrooms is controlled independently from other rooms, was observed. With a two-zone MVHR solution, the thermal conditions in bedrooms can be improved and the space-heating demand can be reduced.

Scottish Passive House: Insights into Environmental Conditions in Monitored Passive Houses

Climate change and sustainability legislation in recent years has led to significant changes in construction approaches in the UK housing sector. This has resulted in the adoption of new building typologies, including the German Passivhaus (Passive House) standard. This standard aims to improve occupant comfort and energy efficiency, potentially changing the ways in which homes operate and how occupants interact with them. With increasing construction of low energy dwellings, there is an emerging gap in knowledge in relation to occupant health and wellbeing, thermal comfort, and indoor air quality (IAQ). Using data collected from a two year Building Performance Evaluation (BPE) study funded by Innovate UK, the environmental data (temperature, relative humidity and carbon dioxide concentrations) from five Certified Passive House homes in Scotland was compared. The results demonstrate problems with overheating with peak temperatures exceeding 30 °C. Imbalanced mechanical ventilation with heat recovery (MVHR) systems were identified in 80% of the dwellings and inadequate IAQ was found due to poor ventilation. Only one of the Passive Houses studied exhibited thermal conditions and IAQ which were, on the whole within Passive House parameters. This paper outlines the insights and the main issues of Scottish Passive House in the broader context of sustainability.

An investigation of indoor air quality, thermal comfort and sick building syndrome symptoms in UK energy efficient homes

Purpose – Concern of the deterioration of indoor environmental quality as a result of energy efficient building design strategies is growing. Apprehensions of the effect of airtight, super insulated envelopes, the reduction of infiltration, and the reliance on mechanical systems to provide adequate ventilation (air supply) is promoting emerging new research in this field. The purpose of this paper is to present the results of an indoor air quality (IAQ) and thermal comfort investigation in UK energy efficient homes, through a case study investigation. Design/methodology/approach – The case study dwellings consisted of a row of six new-build homes which utilize mechanical ventilation with heat recovery (MVHR) systems, are built to an average airtightness of 2m3/m2/hr at 50 Pascal’s, and constructed without a central heating system. Physical IAQ measurements and occupant interviews were conducted during the summer and winter months over a 24-hour period, to gain information on occupant activities, perception of the interior environment, building-related health and building use. Findings – The results suggest inadequate IAQ and perceived thermal comfort, insufficient use of purge ventilation, presence of fungal growth, significant variances in heating patterns, occurrence of sick building syndrome symptoms and issues with the MVHR system. Practical implications – The findings will provide relevant data on the applicability of airtight, mechanically ventilated homes in a UK climate, with particular reference to IAQ. Originality/value – IAQ data of this nature is essentially lacking, particularly in the UK context. The findings will aid the development of effective sustainable design strategies that are appropriate to localized climatic conditions and sensitive to the health of building occupants.

Prefabricated Timber Frame Façade with Integrated Active Components for Minimal Invasive Renovations

The objective of the EU-funded project iNSPiRe is to tackle the problem of high-energy consumption by producing systemic renovation packages that can be applied to residential and tertiary buildings. The renovation packages aim to reduce the primary energy consumption of a building to lower than 50 kWh/(m2 a) for ventilation, heating/cooling, domestic hot water and lighting. The packages need to be suitable for a various climates in Europe while ensuring optimum comfort for the building users. One major aspect of iNSPiRe is the development of multifunctional renovation kits that make use of innovative envelope technologies, energy generation (including RES integration) and energy distribution systems. The technologies and renovation approaches developed by the iNSPiRe project will be installed and tested in three demo buildings. In this work the development, testing and modelling of a timber frame façade with integrated mechanical ventilation with heat recovery (MVHR) and a micro- heat pump (μ-HP) is presented. Three functional models were built for testing in so-called PASSYS test cells for the assessment of the thermal performance and for testing in the acoustic test rig at UIBK. Experimental results are used to validate a physical heat pump and MVHR model. The μ-HP with MVHR is a cost-effective and compact solution for ventilation and heating/cooling for buildings with high standard such as PH or EnerPHit. The integration of active components such as the MVHR and μ-HP in a prefabricated façade enables minimized space use and reducing installation time and effort.

Façade-integrated MVHR with speed-controlled micro-heat pump.

The majority of existing building stock in Europe and worldwide is poor energy performance buildings and renovation plays a major role in achieving climate protection and energy independence. Deep renovation solutions in combination with integrated HVAC systems are developed within the framework of the European project iNSPiRe. The development, testing and modelling of a facade integrated micro-heat pump (µ-HP) in combination with mechanical ventilation with heat recovery (MVHR) is presented. A detailed physical model of the µ-HP is developed within the Matlab simulation environment. The vapour cycle and the air heating/cooling are modelled in steady state to derive the thermodynamic states of the refrigerant and of the air. The refrigerant cycle and the governing equations for the moist air are solved iteratively. Two functional models (dimensions: 2.75 m x 2.75 m) were built for the tests in PASSYS test cells, which allow controlling the temperature with high-power heater and cooler. With a so-called cold box the external boundary conditions can be emulated. Experimental results are used to validate the physical heat pump and MVHR model. The physical model is used to create the performance map data for building and system simulation. Combined building and HVAC simulations are performed to investigate the energy performance of the µ-HP on building level. The performance of the system is investigated for different renovation standards (EnerPHit and Passive House) and for seven different European climate conditions. Different control strategies are investigated and a frosting model is used to optimize defrosting control and thus to reduce energy demand. A functional model will be later monitored in a demo building in Ludwigsburg, Germany. The example of social housing built in the 1970s contains four flats on four stories. The main advantages of the µ-HP are the compactness, providing the possibility of integration into the facade, and cost reduction.

Natural Ventilation with Heat Recovery: A Biomimetic Concept

In temperate countries, heat recovery is often desirable through mechanical ventilation with heat recovery (MVHR). Drawbacks of MVHR include use of electric power and complex ducting, while alternative passive heat recovery systems in the form of roof or chimney-based solutions are limited to low rise buildings. This paper describes a biomimetic concept for natural ventilation with heat recovery (NVHR). The NVHR system mimics the process of water/mineral extraction from urine in the Loop of Henle (part of human kidney). Simulations on a facade-integrated Chamber successfully imitated the geometry and behaviour of the Loop of Henle (LoH). Using a space measuring 12 m2 in area and assuming two heat densities of 18.75 W/m2 (single occupancy) or 30 W/m2 (double occupancy), the maximum indoor temperatures achievable are up to 19.3 °C and 22.3 °C respectively. These come with mean relative ventilation rates of 0.92 air changes per hour (ACH) or 10.7 L·s−1 and 0.92 ACH (11.55 L·s−1), respectively, for the month of January. With active heating and single occupant, the LoH Chamber consumes between 65.7% and 72.1% of the annual heating energy required by a similar naturally ventilated space without heat recovery. The LoH Chamber could operate as stand-alone indoor cabinet, benefitting refurbishment of buildings and evading constraints of complicated ducting, external aesthetic or building age.

Case study investigation of indoor air quality in mechanically ventilated and naturally ventilated UK social housing

There is a significant lack of indoor air quality research in low energy homes. This study compared the indoor air quality of eight newly built case study homes constructed to similar levels of air-tightness and insulation; with two different ventilation strategies (four homes with Mechanical Ventilation with Heat Recovery (MVHR) systems/Code level 4 and four homes naturally ventilated/Code level 3). Indoor air quality measurements were conducted over a 24 h period in the living room and main bedroom of each home during the summer and winter seasons. Simultaneous outside measurements and an occupant diary were also employed during the measurement period. Occupant interviews were conducted to gain information on perceived indoor air quality, occupant behaviour and building related illnesses. Knowledge of the MVHR system including ventilation related behaviour was also studied. Results suggest indoor air quality problems in both the mechanically ventilated and naturally ventilated homes, with significant issues identified regarding occupant use in the social homes.