Ventilation & Overheating BSRIA 22 nd July 2015 Chris Yates, - - PowerPoint PPT Presentation

Ventilation & Overheating

BSRIA 22nd 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
• r 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 < 20.5oC Not significant ≥ 20.5oC and <22.oC Slight ≥ 22.0oC and <23.5oC Medium ≥ 23.5oC 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 Minimum rate Continuous extract Minimum high rate Minimum low rate Kitchen 30 l/s adjacent to hob;

• r 60

60 l/s elsewhere 13 l/s Total extract rate should be at least the Utility room 30 l/s 8 l/s Whole dwelling Bathroom 15 l/s 8 l/s Ventilation rate Sanitary accommodation 6 l/s 6 l/s given in Table 5.1b

Part F - Table 5.1b Whole dwelling ventilation rates

Number of bedrooms 1 2 3 4 5 Whole dwelling ventilation rate (l/s) 13 17 21 25 29 Whole dwelling ventilation rate is based on 2

• ccupants in the main bedroom and single
• ccupant in other bedrooms. For greater level of
• ccupancy, add 4l/s per occupant

Natural ventilation rates

• Effective air change rates per hour – App P

Window Detail Trickle vents

• nly

Windows slightly open (50mm) Windows open half the time Windows fully

• pen

Single storey dwelling Bungalow Flat Cross ventilation possible 0.1 acph 0.8 acph 3 acph 6 acph Single storey dwelling Bungalow Flat Cross ventilation not possible 0.1 acph 0.5 acph 2 acph 4 acph Dwelling of two storeys or more Windows upstairs and downstairs Cross ventilation possible 0.2 acph 1.0 acph 4 acph 8 acph Dwelling of two storeys or more Windows upstairs and downstairs Cross ventilation not possible 0.1 acph 0.6 acph 2.5 acph 5 acph

Ventilation by house type

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

Single aspect apartment Dual Aspect apartment Mid-terrace house Detached House Large detached house Floor Area 55 m2 58 m2 76 m2 118 m2 212 m2 Minimum high rate (boost rate) 21 l/s 21 l/s 35 l/s 43 l/s 64 l/s Minimum background ventilation rate (normal rate) 17 l/s 17 l/s 23 l/s 35 l/s 51 l/s Purge flow rate to achieve 4 air changes per hour 153 l/s 161 l/s 211 l/s 328 l/s 589 l/s

Managing expectations of MEV

• MEV and MVHR designed for minimum SFP and

maximum efficiency

• Airflow range to accommodate Purge rate too wide from
• ne 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

• verheating can be minimised
• Ventilation alone will not eliminate
• verheating

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