A VE-Users Guide to Successful Building Regulations Part O Dynamic Simulation Assessments.

1. Keep Your Cool with the
Building Regulations Part O
www.iesve.com
A VE-Users Guide to Successful Building Regulations
Part O Dynamic Simulation Assessments
Richard Tibenham & Eric Roberts

2. Dr Eric Roberts
Senior Business
Development
Manager
(Software Sales)
Richard Tibenham
UK Business
Development Manager
(Consultancy)

3. Agenda
▪ Overview of Approved Document Part O.
▪ Building Physics Fundamentals – Energy Balance.
▪ IES VE – ADO Templates.
▪ Modelling MVHR systems using IES ApacheSim & IES ApacheHVAC software.
▪ Modelling MEV systems using IES ApacheSim & IES ApacheHVAC software.
▪ The inclusion of internal doors & voids.
▪ ADO weather scenarios vs reality.
▪ Q&A
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4. Approved Document Part O - Overview

5. www.iesve.com
The Building Regulations Part O – An Overview
• Effective for BR’s applications from 15th June 2022 and all
projects commencing onsite from 15th June 2023.
• Applicable in England Only.
• Applicable for all residential buildings including dwellings
and any institutional premises where people sleep (except
hotels).
• Requires buildings to manage overheating risks based on a
‘Simplified Method’ or ‘Dynamic thermal modelling’
method.
• Outlines additional considerations with respect to Noise,
Pollution, Security, Protection from falling, and Protection
from Entrapment.
• Outlines details concerning the provision of information to
building users under the ‘Staying cool in hot weather’
section of the Part L home user guide.

6. www.iesve.com
The Building Regulations Part O – ‘Simplified Method’
• Provides limiting values for glazed area depending upon cross-
ventilation / no cross ventilation scenarios.
• Provides limiting values for free-opening area depending upon
cross-ventilation / no cross ventilation scenarios.
• Solar shading required for buildings in ‘high risk’ locations
(Central London).
• The simplified method is not suitable for buildings with more
than one residential unit which use a communal heating or hot
water system with significant amounts of horizontal heating or
hot water distribution pipework.
• The simplified method is simple and low-cost, but limits design
flexibility.
• The simplified method will provide less accurate results than
the ‘Dynamic Thermal Modelling’ method, which could expose
clients to higher risks associated with occupant’s satisfaction
levels.

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The Building Regulations Part O – ‘Dynamic thermal modelling’
• Provides greater design flexibility through the use of a dynamic thermal
modelling approach.
• Adopts the ‘CIBSE TM59’ thermal comfort standard as a basis for the
assessment.
• CIBSE TM59 adopts an ‘adaptive comfort model’ for the evaluation of
‘predominantly naturally ventilated homes’, based on a weighted running
mean average of the external air temperature.
• The assessment of overnight temperatures and the assessment of
‘predominantly mechanically ventilated homes’ adopt a fixed overheating
threshold temperature of 26⁰C.
• Bedrooms are deemed to overheat if room temperatures >26°C for more
than 32 hours during the period 22:00- 07:00
• Predominantly mechanically ventilated homes are considered to overheat
if room temperatures >26°C for more than 3% of annual occupied hours.
• The BR’s Part O qualifies CIBSE TM59 modelling parameters concerning
window opening characteristics and the use of internal shading systems.

8. www.iesve.com
The Building Regulations Part O – Notable Points
• ADO defines the parameters by which external opens (windows & doors) shall
be controlled.
• ‘Easily accessible’ windows are assumed closed between 11pm and 8am
unless fixed or lockable louvred shutters or window grilles/railings are
specified.
• This presents an overheating risk in ‘easily accessible’ bedrooms which
should be considered during the design stage.
• The inclusion of internal blinds is not permitted for Part O modelling.
• The ‘protection from falling’ element of Part O combined with the item 2.10
a) iii of the BR’s Part B (fire safety) dictates that an emergency escape
window must have a sill height of exactly 1,100mm above FFL (no greater, no
less), unless guarding is specified.
• Part O suggests that windows are likely to be closed if noise levels exceed
specified limits during the night. The overheating risk associated with this
should be considered during the design stage.
• Buildings located near to significant local pollution sources should be
designed to minimize the intake of air pollutants. The overheating risk
associated with this should also be considered.

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Energy Gains > Energy Losses = Temperature Rise
Energy Balance
Energy Gains < Energy Losses = Temperature Fall
Control of energy gains and energy losses allows
the temperature of a building to remain stable.

10. www.iesve.com
Active Space Heating
Solar Heat Gain
Ventilation Heat Gain
Infiltration Heat Gain
Thermal Envelope Conductive & Radiant Heat Gain
Occupancy Heat Gain
Lighting Heat Gain
Equipment Heat Gain
DHW Distribution & Storage Heat Gain
Active Space Cooling
Ventilation Heat Loss
Infiltration Heat Loss
Thermal Envelope Conductive & Radiant Loss Gain
Energy Gains Energy Losses
Thermal Mass
Energy Balance
High energy demand
& high carbon
emissions modes of
control.

11. www.iesve.com
To maintain comfortable summer temperatures
(without active space cooling):
When the internal air temperature is
above the external air temperature:
When the internal air temperature is below
than the external air temperature:
• Reduce solar heat gain.
• Reduce internal heat gains.
• Increase heat loss via natural ventilation.
• Increase heat loss via mechanical ventilation
(without heat recovery).
• Thermal insulation and air tightness are not
desirable.
• Reduce solar heat gain.
• Reduce internal heat gains.
• Reduce conductive heat gains.
• Reduce infiltration heat gains.
• Reduce heat gain via natural ventilation.
• Reduce heat gain via mechanical ventilation
(with heat recovery).
• Thermal insulation and air tightness are
desirable.
Elevate the transfer of heat loss from
inside to outside.
Restrict the transfer of heat gain from
outside to inside.

12. www.iesve.com
Case Study Dwelling:
• New build dwelling.
• Built to AD Part L 2021 & Part O
2021.
• Trad’ build construction type.
• Triple glazed windows.
• MVHR unit with summertime
by-pass.
• Case study assumes compass
orientation with glazing
predominantly to the south.

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Solar heat gain incurs ~50% heat
gains during the summer
Space heating system provides
dominant heat gain during the
winter
Natural ventilation provides dominant
heat loss during the summer

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Solar heat gain presents dominant
mode of heat gain during the day
Natural ventilation presents
dominant mode of heat loss
Conductive heat loss via the
construction fabric presents
second highest mode of heat loss

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Design Features to Prevent Summertime Overheating in
Dwellings (and comply with the BR’s Part L):
1. Maximise wintertime solar heat gain & minimise summertime solar heat gain. Glazing should
predominantly be south facing with seasonal shading (overhangs, solar control glass, external blinds etc).
Avoid large areas of west facing glazing.
2. If present, equip large west facing windows with a means of external shading. Solar heat gains from
west facing glazing is a prominent driver of over heating risks.
3. Allow windows to open as widely as possible with causing a safety risk. Consider how windows might
interact with shading measures (eg. Inward opening windows and internal blinds).
4. Ensure that adequate night time ventilation is provided to ‘easily accessible’ bedrooms, and rooms
where acoustic noise and air pollution are present. This will likely require a mechanical ventilation
solution.

16. Approved Document Part O
IES Templates

17. www.iesve.com
The ADO Templates:
ADO internal
heat gain
profiles.
ADO MacroFlo
window
opening types.

18. Modelling MVHR & MEV
Ventilation Systems using
IES ApacheSim and
IES ApacheHVAC modules

19. www.iesve.com
Mechanical Ventilation vs. Natural Ventilation
• The primary purpose of
mechanical ventilation systems
is to maintain adequate air
quality.
• The space cooling function is
typically a consequence of the
primary function.
• Mechanical ventilation rates are
typically far lower than natural
ventilation rates.
• A mechanical ventilation system
sized for the maintenance of air
quality is not a substitute for
natural ventilation for the
purposes of space cooling.
Natural ventilation air volume
Boosted mechanical
ventilation air volume
Background mechanical
ventilation air volume

20. www.iesve.com
MVHR (Mechanical Ventilation
with Heat Recovery):
MVHR Modelling within IES VE Software
Modelling routes:
- IES ApacheSim.
- IES ApacheHVAC.
Modelled Characteristics:
- Background (trickle) air supply and extract rates.
- Boosted ventilation rates.
- Heat recovery by-pass controls.
- ‘Night time purge’ control logic.
Image courtesy of https://ventilationmegastore.co.uk/

21. Modelling MVHR using
IES ApacheSim

22. www.iesve.com
26l/s
19l/s
5l/s
19l/s
13l/s
13l/s
Representation of MVHR modelling using IES ApacheSim:
Lounge
Dining
Room
Kitchen
Utility
Shower
Bedroom
5l/s
13l/s
13l/s
19l/s
19l/s
26l/s

23. www.iesve.com
MVHR set up using IES ApacheSim:
Defines the mechanical ventilation air exchange rate.
Defines the air exchange rate variation profile.
Defines free-cooling flow capacity (ventilation
without heat recovery).
Defines the HVAC system type.
Defines MVHR fan SFP. Must be ticked to
include mechanical ventilation & extract
modelling.

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MVHR set up using IES ApacheSim:
Defines the heat recovery by-pass damper operational
profile and set-point(s).
Defines space heating operational profile and set-
point(s).

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Modelling ‘Boost’ Functionality in IES ApacheSim:
Boost function flow rate
Air Exchange tab
Boost function variation
profile
Boost function adjacent
air condition (assumes
external air condition
without heat recovery)
Daily boost functionality flow rate
variation profile
Annual boost functionality flow rate
variation profile
CIBSE TM59 Guidance:

26. www.iesve.com
MVHR set up using IES ApacheSim:
Room air temperature
profile with fan speed
and HR bypass damper
controls targeting 22°C
(day) & 18°C (night).
Room air temperature
profile with fan speed
and HR bypass damper
controls targeting 20°C
(day) & 16°C (night).

27. www.iesve.com
MVHR set up using IES ApacheSim:
MVHR background
rate air volume.
Room air temperature.
MVHR ‘boosted
rate’ air volume.

28. Modelling MVHR using
IES ApacheHVAC

29. www.iesve.com
26l/s
19l/s
5l/s
19l/s
13l/s
13l/s
Representation of MVHR modelling using IES ApacheHVAC:
Lounge
Dining Room
Kitchen
Utility
Shower
Bedroom
Zonal supply &
extract calculated
via IES ApacheHVAC
Air transfer path
calculated using IES
MacroFlo

30. www.iesve.com
MVHR modelling using IES ApacheHVAC:
MVHR Supply fan speed
controls, including background,
PIR, summertime boost &
summertime night time purge
controls.
Fixed volume junctions/room
dampers.
Supply ventilation zones.
IES MacroFlo calculates air
movement between supply and
extract ventilation zones.
Extract ventilation zones.
MVHR Extract fan speed
controls (mirror of supply fan
controls).
Heat recovery controls
(summer & winter mode).
Network Features:
- Separate supply and extract
zones.
- Air transfer path between
supply and extract zones
modelled via Macroflo.
- Detailed heat recovery
controls for summer and
wintertime set-points.
- Variable rate fan speeds
based on average return air
temperature to the MVHR
unit, including background
and ‘boost’ rates.

31. www.iesve.com
MVHR modelling using IES ApacheHVAC:

32. www.iesve.com
MVHR Modelling ApacheSim vs. ApacheHVAC:
Air temperature using ApSim
Air temperature using ApHVAC
Air temperature using ApHVAC
Air temperature using ApSim

33. Modelling MEV systems using IES
ApacheSim

34. www.iesve.com
19l/s
13l/s
13l/s
Representation of MEV modelling using IES ApacheSim:
Lounge
Dining Room
Kitchen
Utility
Shower
Bedroom
Balance air equal to the extract air
volume is assumed. The
temperature of balance can be set
to;
- External Air.
- External Air + offset profile.
- Temperature from a profile.
- Ventilation from adjacent room.
13l/s
13l/s
19l/s

35. www.iesve.com
Modelling the Adjacent Condition for Balance Air:
The adjacent air
condition defines the
balance air temperature
ONLY.
When set to ‘Ventilation
from Adjacent Room’ it
DOES NOT model a
pressure drop in the
adjacent room.
IES ApacheHVAC is recommended for
scenarios where cMEV and dMEV are
intended to serve a space cooling function
for rooms in the air transfer path.

36. Comparison of MEV system
Modelling in IES ApacheSim &
IES ApacheHVAC

37. www.iesve.com
MEV modelling using ApHVAC; MEV modelling using ApSim;
Bedroom
Bedroom
Air transfer path
is modelled.
Air transfer path
is not modelled.
Extract
ventilation
terminal
Extract
ventilation
terminal

38. www.iesve.com
MEV modelling using ApHVAC vs. ApSim
Room air temperature
(ApSim modelling).
Room air temperature
(ApHVAC modelling).
ApHVAC method
achieves lower night
time room
temperatures when
‘accessible windows’
are closed.
Likelihood of
achieving ADO
compliance is
improved.

39. The Inclusion of Internal Doors

40. www.iesve.com
IES ApacheSim modelling with/without internal door
and void modelling:
Room air temperature
with internal door
modelling.
Room air temperature
without internal door
modelling.

41. DSY Weather Data vs. Reality

42. www.iesve.com
Birmingham DSY1 2020 50th percentile vs. Birmingham AMY 2022

43. Richard.Tibenham@iesve.com
Eric.Roberts@iesve.com
Thank you.
Q & A
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