Characteristics and performance of MVHR systems A meta study of heat recovery ventilation systems in new dwellings FM Nectar Presented by: Ian Mawditt, fourwalls Consultants Professor Rajat Gupta, Oxford Brookes University, Oxford Institute for Sustainable Development HVAC 2016: UK Construction Week 18 th October 2016 Study by: Supported by:
MVHR Meta-study slide 2 Meta study of MVHR systems in domestic properties Main objectives: To gather and analyse the available performance data from MVHR-ventilated (domestic) properties within the BPE* Portfolio To gather information about performance, and how they are being maintained and used To share this information within projects and to the wider construction industry * BPE Building Performance Evaluation Programme - 8M programme operated and funded by Innovate UK
MVHR Meta-study slide 3 MVHR meta study 237 dwellings with MVHR in BPE portfolio 85 study dwellings across 29 developments Development sizes range from 1 to 700 54 systems with detailed characteristics 21 with consistent monitored data (incl. CO 2 ) Some limitations with the data General comparative analysis BUS Methodology re-analysed on 27 projects 15 project teams interviewed
H14_a1 H8_b1 F1_d1 H5_a1 H10_a1 F12_b1 F11_b1 H16_a1 H15_c1 F1_b1 H8_a1 H15_c2 H17_b1 F7_a1 F7_b1 F11_d1 F19_a1 H15_a2 H17_d1 H11_d1 H15_a1 H6_a1 H17_d2 H17_c1 H11_a2 H6_b1 F11_c1 H11_c1 H11_d2 H19_a1 H11_b2 F11_a1 H19_b1 H15_b1 H11_b1 H11_c2 H11_a1 Carbon Dioxide (ppm) MVHR Meta-study slide 4 Comparative performance MVHR and non-mvhr Chart shows peak carbon dioxide (CO 2 ) levels in bedrooms during February 5000 4500 Feb Peak CO2 (MVHR) Feb Peak CO2 (Non-MVHR) Clear difference between MVHR and non-mvhr ventilation types 4000 3500 3000 Impact on CO 2 most evident in winter less window opening? * or bold stack on any charts indicate certified Passivhaus 2500 2000 1500 1000 500 * * * * * * * * * * * * * * 0
Percentage of monitored bedrooms MVHR Meta-study slide 5 Comparative performance MVHR and non-mvhr Chart shows peak CO 2 levels across winter, spring and summer CO 2 is still higher in non-mvhr dwellings through spring and summer Increasing CO 2 levels in MVHR dwellings in summer may indicate shift toward natural vent during warmer periods 100% 80% 60% 40% 20% Percentage 1000 ppm Percentage >1000, <1500 ppm Percentage 1500 ppm 0% MVHR Non-MVHR MVHR Non-MVHR MVHR Non-MVHR February April August
MVHR Meta-study slide 6 CO 2 concentration a useful metric? Correlation between poor ventilation and indoor pollutants Formaldehyde: a known carcinogen Chart with permission: MEARU
H9_a1 H14_a1 H3_h1 H3_f1 H20_c1 H3_f2 H3_h2 F7_c1 H3_e2 H20_b1 H3_e1 F12_a1 H3_g1 H15_a2 H17_d1 F7_b1 H15_c1 H17_d2 H3_g2 F1_b1 H9_a1 F12_b1 H3_a1 H8_b1 F7_a1 F1_d1 H15_a1 H11_d2 F11_b1 H17_b1 H19_b1 H11_c2 F19_a1 H20_d1 F11_c1 H17_c1 H15_b1 H15_c2 F4_b1 H11_d1 F11_a1 H11_c1 H11_b1 H11_b2 H11_a1 H8_a2 H6_a1 H6_b1 F11_d1 H8_a1 H16_a1 Relative Humidity Variance (%RHv) MVHR Meta-study slide 7 Relative humidity range MVHR and non-mvhr Chart shows RH variance during February between MVHR and non-mvhr dwellings 50 45 40 February Range (MVHR) February Range (Non-MVHR) Greatest RH stability evident in MVHR dwellings and close to optimal conditions during all monitored seasons Note that RH is influenced by numerous factors (i.e. not just down to ventilation) 35 30 25 20 15 10 5 * * * * * * * * * * * * * * * * 0
F1_d F12_b F7_a F7_c F7_b H8_a F4_a H14_a H16_a H10_a F1_b H3_f H20_c F4_b H3_b H5_a H20_d H3_g H3_h H3_e H20_b F1_e H3_d H14_b H8_b H6_a H15_a H3_a H9_a H9_b H6_b H17_c H15_c H17_d H11_d F19_a H19_a H15_b F11_c F11_b H11_b F11_d H17_b H11_c H19_b F11_a H11_a Temperature Variance ( Cv) MVHR Meta-study slide 8 Summer temperature range MVHR and non-mvhr Chart shows temperature ranges during August between MVHR and non-mvhr dwellings 20 18 16 Aug Temp Range (MVHR) Aug Temp Range (Non-MVHR) Greatest temperature stability evident in MVHR dwellings 14 12 Is this a good thing? Recent research suggests: Temperature fluctuations may be beneficial for health Lack of temperature stimulation may lead to thermal monotony 10 8 6 4 2 0 * * * * * * * * * * * * * *
MVHR Meta-study slide 9 Does it all seem a bit rose-tinted so far? Let s remove the glasses and look (briefly) at some challenges found with MVHR
H8_a* H23_a* F12_b* F7_b* H23_b* F7_a* H28_a* F12_a* H5_a* H8_b* H31_a* F23_a* H28_b* F7_c* H22_a H15_c* H14_a* H14_b* H34_a H20_a H17_b* F34_a F37_a F36_a H17_a* H20_d F37_a H17_c* F37_a H33_a F36_b H29_a H20_c H20_b F36_c H26_a H26_b H29_b H25_a F4_a H24_a H21_a H32_b F4_b H35_a H32_a H24_b F27_a H30_b H24_d H30_a H9_a H24_c H24_e (m 3 /h)/m 2 @50Pa MVHR Meta-study slide 10 Air permeability range Measured values: 44% > 3 (m 3 /h)/m 2 @50Pa 27% > 5 (m 3 /h)/m 2 @50Pa 19 Passivhaus < 3 (m 3 /h)/m 2 @50Pa 10 9 8 7 Tested Air Permeability Design Air Permability Design Values: n<1.0 = 20; n>1.0<3.0=21; n>3.0<5.0=10; n>5.0 = 3 Mean 3.2 (m 3 /h)/m 2 @50Pa 6 5 4 3 2 1 0
litres per second MVHR Meta-study slide 11 Measured flow rates: comparison to Approved Document F 68% AD F (2006) systems met minimum required air flow rate. Only 23% of AD F 2006 systems in airtight homes were found to have higher (e.g. AD F 2010) flow rates Two systems failed significantly Only 33% AD F (2010) air flow rates met the minimum specification (chart not shown) * or bold stack on any charts indicate certified Passivhaus 45 40 35 30 25 20 15 10 5 0 Measured Flow Rate (Supply) Measured Flow Rate (Extract) Minimum for Part F (2006) Minimum for Part F (2010) n(2006) = 34 (n < Part F = 11; n < Design = 14)
Litres per second (l.s-1) MVHR Meta-study slide 12 Individual (wet) room extract high rates Minimum boost rate met in: 44% kitchens 71% bathrooms 30% en-suites 38% utility rooms 77% sanitary acc. 25.00 20.00 15.00 10.00 5.00 0.00 n = 48 Max Value n<13 l/s = 27 Min Value n = 48 Median Upper Quartile n = 10 n<8 l/s = 14 n<8 l/s = 7 Lower Quartile n = 8 Minimum AD F Kitchen Bathroom En Suite Utility W.C. n = 30 n<8 l/s = 5 n<6 l/s = 7
F7_a* H31_a* H5_a* H15_c* H8_b* H28_b* H29_b H8_a* H28_a* H20_b H20_d F37_a H29_a H17_a* H20_c F36_c H17_b* H14_b* H17_c* F7_b H33_a F36_b H32_b F4_a F36_a H21_a H20_a F7_c* F12_b* F4_b H25_a F37_a H30_a H35_a H22_a H24_e F37_a H30_b H32_a F12_a* H14_a H9_a H34_a H26_a H26_b F27_a F34_a MVHR Meta-study slide 13 System balance Illustration of % imbalance between total supply and extract rates Supply and extract rates should be balanced (theoretical 0%) An imbalance of up to 15% is acceptable (PH limit is 10%) 48% of systems had an imbalance 15% Impact on heating energy difficult to quantify High imbalance could cause condensation problems 100 + 90 80 70 60 50 40 30 20 10 0
MVHR Meta-study slide 14 Feedback from design/construction teams and users Re-analysis of BUS survey results: Occupant satisfaction (n=27 projects covering 211 dwellings) Online questionnaire survey (n=15 projects covering163 dwellings) Semi-structured interviews (telephone) (n=14 projects covering 158 dwellings) Design and procurement stage Construction and installation stage Post-completion stage In-use stage
MVHR Meta-study slide 15 BUS Methodology re-analysis user satisfaction (n=27) BUS Methodology end-user / occupant survey relating to comfort levels Chart shows aggregated results from 27 projects Despite problems with correct commissioning, occupants are mostly satisfied with comforts conditions (relating to perception of air quality)
MVHR Meta-study slide 16 Design and procurement stage (n=15) Design intent Survey / questionnaire results Passivhaus (Ph) projects: n=7 / non-ph projects: n=8 What was the design intent in terms of sustainability standards? Passivhaus Building Regulations 2006 Code for sustainable homes level 4 Code for sustainable homes level 5 FEES Scottish Building Regulations 2009 NI building Regs 0 1 2 3 4 5 6 7 8
MVHR Meta-study slide 17 Design and procurement stage (n=15) Most considered at design stage: location of MVHR unit Least considered at design stage: Maintenance How well were the following aspects considered at the design stage? Location of the MVHR unit Location of outlet terminals Integration of ductwork Location of control switches Location of boost switches Maintenance regime Access to filters Usability of the system and controls Acoustic design 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Poor Moderate Good Not enough information to comment No comment
MVHR Meta-study slide 18 Construction and installation stage (n=15) Most respondents confirm the MVHR system was installed as-designed and were satisfied with: Location of outlet terminals (n=10) and Accommodation of the system within the structure (n=8). Most dissatisfaction related to: Ducts: One-third of the respondents reported plastic (rigid) ductwork as main type used, More than half reported some instances of flexible ductwork. Installer procedures and competence (n=6) and Quality of ductwork (n=6) Most common commissioning issue was an imbalance between supply and extract airflows (n=7)
MVHR Meta-study slide 19 Post-completion and handover stage (n=15) Over half the projects (n=8) provided occupant training on use and maintenance of MVHR, and followups About 10 projects provided operational instructions over and above manufacturers guidance. What guidance or training were provided to the occupants to operate the MVHR system? Manufacturer's guidance only Follow-up a few weeks after occupancy to gauge user understanding Training with technical expert Training with tenant/customer liaison officer Specific instructions for maintenance (such as changing of filters) of MVHR system Specific instructions for operating the MVHR system Instructions provided as part of Home user guide 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Yes No Don't know
MVHR Meta-study slide 20 In-use stage (n=15) A majority of systems achieve good IAQ and satisfactorily control moisture levels Is the ventilation system performing as intended? Supply/extract meeting building regulations Achieves good indoor quality Controls moisture levels Boost sufficient for minimum boost flow rate in building regulations Is a humidity/co2 sensor present (that adjusts the ventilation rate) Is the humidity/co2 sensor effective 0% 20% 40% 60% 80% 100% Yes No Don't know / N/A No response
MVHR Meta-study slide 21 In-use stage: operational issues Most prevalent operational issue: Maintenance filter cleaning / replacement Did the occupants experience any operational issues with the MVHR system? Display too complex Imbalance between supply and extract Fan speed too low Fan speeds too high Maintenance - filter cleaning/replacement Continuity of service Unacceptable noise made by the system Low temperature High temperature/overheating 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Yes No Don't know No response
MVHR Meta-study slide 22 In-use stage Performance issues between Passivhaus and non-ph projects IAQ problems Draughts or other discomfort Unacceptable noise Low temperatures High temperatures 0 1 2 3 4 5 6 7 Number of projects with reported issues Passivhaus (n=7) Non-Ph (n=8)
MVHR Meta-study slide 23 Summary Does MVHR work? Yes, when it works well But a lot can go wrong Failure of a ventilation system (or occupant switch off) in a house with no alternative may be a problem 'you can always open the windows but what if you can t?... or don t?
MVHR Meta-study slide 24 Conclusions Ventilation is not being adequately designed Too low on the priority list, leading to poor integration and quality MVHR was adopted for achieving high code compliance in most projects Compliance if met at design stages not seen through to commissioning stages Even after re-commissioning, some of the units did not perform satisfactorily (air flow, noise, cold air, etc.) How can commissioning quality improve? Occupant understanding appeared to be better in dwellings which had a graduated handover, hands-on training and guidance document
MVHR Meta-study slide 25 Conclusions (cont d) In a third of the projects, MVHR was perceived by occupants to be the cause of high fuel bills as it is 'always on and thus disabled. Intent: MVHR used as a cost-effective solution for ventilation Poor overview of the whole process Systems often fitted with a fit and forget mentality Maintenance someone else s problem! Contrary to manufacturer guidance, filters had to be changed every 3 months (at least) Questions remain: What conditions can be maintained with a sub-optimal system performance? What are the energy penalties for under-performance?
MVHR Meta-study slide 26 Much more detail in the report Review of design information Review of commissioning data Performance relating to duct types Energy use analysis Qualitative data from interviews Case studies Download at: www.fourwalls-uk.com/mvhr-meta-study architecture.brookes.ac.uk/research/lowcarbonbuilding/ radar.gsa.ac.uk/4073/