Ventilation & Overheating BSRIA 22 nd July 2015 Chris Yates, Managing Director Johnson & Starley
Agenda • Government’s position on Zero Carbon homes • Definition of overheating • Overheating – factors • Ventilation – definition, SAP and Part F • Calculating ventilation requirements
Government’s Productivity Plan “The Government will repeat its successful target from the previous Parliament to reduce net regulation on house builders. The government does not intend to proceed with the zero carbon Allowable Solutions carbon offsetting scheme, or the proposed 2016 increase in on-site energy efficiency standards, but will keep energy efficiency standards under review, recognising that existing measures to increase energy efficiency of new buildings should be allowed time to become established”
Overheating – definition The Zero Carbon Hub’s working definition of Overheating: “ The phenomenon of a person experiencing excessive or prolonged high temperatures within their home, resulting from internal and/or external heat gains, which leads to adverse effects on their comfort, health or productivity .”
Overheating – a number of factors • Location: The climate tends to be hottest in south east England, dense urban neighbourhoods are at higher risk • Fabric characteristics: Highly insulated homes, darkly coloured external walls, sky lights or large areas of un- shaded south, east or west facing glazing. • Occupancy/behaviour: at home all day can be at high risk, temperatures higher in the early afternoon. • Orientation and exposure: Homes with windows facing east or west and which are exposed to the sun can be at risk. • Type of property: Top floor flats can absorb a lot of heat through the roof and can be more exposed to direct solar radiation
Ventilation • Ventilation is the main method of removing heat from dwellings in the UK • Providing the outside air is cooler than inside ventilating a dwelling with fresh air will help to lower the internal temperature • Air movement over the skin also has a perceived cooling effect
BUT FIRST……..
Who are we? • UK manufacturer based in Northampton • Company started in 1922 • First MVHR for domestic use installed in 1984 • Produce Climate Controlled Air Movement Systems for domestic, commercial & industrial – Warm air – Ventilation – Heat Interface Units And… – Gas boilers
SAP - Overheating & Space Cooling • SAP is being reviewed in 2015 and 2018 with DCLG evidence • Overheating in SAP will be based on further research from DCLG and others, particularly if it leads to ventilation changes to improve performance • SAP design temperatures are: 18°C upstairs, 21°C downstairs • Design temps are not average indoor but set to ensure comfort for the vulnerable determined by the World Health Organisation • BRE are modelling overheating including Part-F scenarios, especially demand controlled ventilation and chimneys • SAP Appendix P (Assessment of internal temperature in summer) uses months of June, July and August only for calculations. Highly insulated property could overheat outside of those months • SAP is not a design tool!
SAP Appendix P • Table P2: Levels of threshold temperature corresponding to likelihood of high internal temperature during hot weather T threshold Likelihood of high internal temperature during hot weather < 20.5 o C Not significant ≥ 20.5 o C and <22. o C Slight ≥ 22.0 o C and <23.5 o C Medium ≥ 23.5 o C High
Overheating & Space Cooling • Part F ventilation systems • Mechanical extract ventilation (MEV) • Mechanical ventilation with heat recovery (MEV) • Part F Building Regulation table 5.1a Ventilation extract rates and table 5.1b whole dwelling ventilation rates • Minimum requirement 0.3 litres/m² floor area, boost extract rates 13 litres/sec from a kitchen and 8 litres/second from a bathroom • 4 air changes per hour for purge ventilation in each habitable room • Purge ventilation is short term immediate response to remove pollutants and moisture, e.g. open the windows • Purge is not covered by Part F for thermal comfort • NHBC Foundation guidance suggests 4 to 5 ACPH are required for thermal comfort ventilation
Part F - Table 5.1a Extract ventilation rates Room Intermittent extract Continuous extract Minimum rate Minimum high rate Minimum low rate Kitchen 30 l/s adjacent to hob; 13 l/s Total extract rate or 60 should be at least 60 l/s elsewhere the Utility room 30 l/s 8 l/s Whole dwelling Bathroom 15 l/s 8 l/s Ventilation rate Sanitary 6 l/s 6 l/s given in Table 5.1b accommodation
Part F - Table 5.1b Whole dwelling ventilation rates Number of bedrooms 1 2 3 4 5 Whole dwelling 13 17 21 25 29 ventilation rate (l/s) Whole dwelling ventilation rate is based on 2 occupants in the main bedroom and single occupant in other bedrooms. For greater level of occupancy, add 4l/s per occupant
Natural ventilation rates • Effective air change rates per hour – App P Window Detail Trickle vents Windows Windows open Windows fully only slightly open half the time open (50mm) Single storey dwelling 0.1 acph 0.8 acph 3 acph 6 acph Bungalow Flat Cross ventilation possible Single storey dwelling 0.1 acph 0.5 acph 2 acph 4 acph Bungalow Flat Cross ventilation not possible Dwelling of two storeys or more 0.2 acph 1.0 acph 4 acph 8 acph Windows upstairs and downstairs Cross ventilation possible Dwelling of two storeys or more 0.1 acph 0.6 acph 2.5 acph 5 acph Windows upstairs and downstairs Cross ventilation not possible
Ventilation by house type Single aspect Dual Aspect Mid-terrace Detached Large detached apartment apartment house House house Floor Area 55 m 2 58 m 2 76 m 2 118 m 2 212 m 2 Minimum high rate 21 l/s 21 l/s 35 l/s 43 l/s 64 l/s (boost rate) Minimum background 17 l/s 17 l/s 23 l/s 35 l/s 51 l/s ventilation rate (normal rate) Purge flow rate to achieve 4 air 153 l/s 161 l/s 211 l/s 328 l/s 589 l/s changes per hour Calculation for single aspect apartment Volume = 55m² x 2.5m (ceiling height) = 137.5m³ Minimum high rate = kitchen + bathroom = 13+8 = 21l/s Minimum background ventilation rate = 55 x 0.3 = 17l/s Purge flow rate = 137.5 x 4 (purge air changes) /3.6 = 153l/s or 1980m³ /hour
Managing expectations of MEV • MEV and MVHR designed for minimum SFP and maximum efficiency • Airflow range to accommodate Purge rate too wide from one unit • MVHR summer by-pass to prevent recovered heat delivered back into dwelling • No cooling effect - provision of minimum background ventilation • Air tight homes make indoor noise more prominent • MEV and MVHR systems running at purge airflow rate would be unacceptable
ErP (Lot 6) description • Thermal by-pass facility means any solution that circumvents the heat exchanger or controls automatically, or manually, its heat recovery performance, without necessarily requiring a physical airflow by-pass,(for example: summer box, rotor speed control, control of airflow). • Examples are: – 100% by-pass – Partial by-pass – Variable speed control – Extract only
Calculation Example • House size = 300m³ • Temperature reduction required = 3° C ∆t • Part F - ventilation rate = 35 litres/second • Q(kW) = q (airlflow m³ /s) x 1.2 (air density m³ /Kg) x 1.01 (specific heat capacity kJ/Kg°C x ∆t • Therefore, Q = 0.035 x 1.2 x 1.01 x 3 = 0.127kW • A provision of 2kW would be required to provide any benefit, therefore airflow would be 550 litres per second or 1980 m³ /hour, in other words, lots of noise and additional cost. Alternatively, open the windows!! • To correct this, consider Fabric First before Ventilation to reduce the requirement
Calculation example contd. • In our experience, 2kW of cooling (Q) would be needed to provide any benefit to the building. • Therefore, the airflow (q) would be calculated as follows: • q (airlflow m³ /s) = Q(kW) / (1.2 (air density m³ /Kg) x 1.01 (specific heat capacity kJ/Kg°C x ∆ t) • q = 2/(1.2 x 1.01 x 3) x 3600 = 1980 m³ /hr
Summary • Despite being a manufacturer of ventilation equipment, we strongly advocate ‘Fabric First’ • SAP is very much an assessment, rather than a design tool • With good planning of the design of the building and services, the effects of overheating can be minimised • Ventilation alone will not eliminate overheating
Useful links • DECC guide to overheating in homes http://www.arcc-network.org.uk/wordpress/wp- content/pdfs/DECC-Overheating-guidance-document- 19Jun2015.pdf • SAP 2012 http://www.bre.co.uk/sap2012/page.jsp?id=2759 • Part F http://www.planningportal.gov.uk/buildingregula tions/approveddocuments/partf
Contact details Chris Yates Managing Director Johnson & Starley Ltd Rhosili Road Brackmills Industrial Estate Northampton NN4 7LZ Telephone : 01604 762881 Mobile : 07827 818247 www.johnsonandstarley.co.uk
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