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NZ
EB
Case S
tudy
: E
SB
Offic
es
Fitzw
illia
m S
t.
Conte
xt
City centre location
6 Stores, rising to the 28m city height limit
2 sub ground floors
Speculative commercial element
Typical Office: Except….
Can be (properly) Naturally ventilated, mixed mode
or air conditioned. Recognizing potential future
trends in energy performance demand.
Due to anomaly in the treatment of mixed mode in
SBEM, it assumes mixed mode uses more energy so
the example also holds for a fully air conditioned
office. (if air conditioned efficiently)
Designed from 2011 to comply with predicted 2020
NZE requirements
FABRIC DESIGNED TO MINIMISE ENERGY DEMAND
• Solar control glazing selected for each elevation
• External shading is solar selective
• Glazed areas limited and optimised to decrease with height (reduced solar gains where un-shaded)
Morning
Afternoon
• Plan depths designed to maximise natural light and ventilation, but within commercial constraints and depths to extend to 22m in places
• Exposed mass is available (as an option) to moderate conditions
• Opaque elements to 0.15 W/m2K
• Glazing to 1.2 W/m2K (triple glazing would increase energy used)
• Air leakage of 1.5
• LED lighting
• Hybrid ventilation (although SBEM treats it as worse than fully air
conditioned)
Air
sourc
e h
eat
pum
p a
nd e
nerg
y t
ransf
er
Effective TER (COP) = 7.8 in heat transfer mode
Phase change storage and high temperature cooling used
(Treatment of heat transfer mode by NZE is up for debate and not
included in savings for the purpose of this study)
NZEB TEST- KEY POINTS ABOUT THE METHOD
• SBEM is used as the calculation method
(not intended as an energy calculation tool)
(doesn’t take into account some forms of energy saving and incorrectly calculates some effects)
(despite its inaccuracies the end result is reasonable in most cases)
• Only interested in building energy not end user energy
• Primary energy and primary carbon are considered
(A 15% additional allowance is made for carbon)
• Reference model inputs are provided so the exact reductions relative to
the current Part L vary form building to building.
-- SBEM
2008 --
Reference Model
Actual Building
Simplified Energy
Model Result
SBEM
Simplified Energy
Model Result
Most Geometry
Air Conditioning types
Light Levels
Fixed Insulation
Fixed Air leakage
Fixed Lighting type
Fixed Heat generation
Fixed Cooling generation
Fixed Glazed area
Fixed Glazing G value
Fixed end user
Activities are
Ignored
Some
Features are
stripped
Reference Model
40% less energy than the 2008 Part L (for this building)
Clearly we need to target lighting, fan energy and cooling to reduce loads
Reducing heating too much could make achieving the renewables target more difficult
1
2
3
Actual Building
The actual building’s energy use is 17% better than the reference building (57%
better than the 2008 regulations)
The actual building’s carbon emissions are 13% lower than the reference building (28% better than the carbon requirement – no need for the 15% additional allowance)
HP
Ad
va
nce
d
co
oin
g
20
0m
2
Air
le
aka
ge
, g
lazin
g
are
a, H
P
LE
D a
nd
ta
sk
de
sig
n
Imp
rove
d fa
n
po
we
r
Acceptable Renewables (in the provisional software):
• PV
• Wind - Not practical for this project
• Solar thermal- PV is more cost effective and has higher primary fr.
• Biomass / Biogas - Expensive in running costs
• CHP - 1% contribution and negative lifetime carbon impact
• Heat pumps
Unacceptable Equivalents that are used in the building:
• Heat transfer (waste heat from the cooling process)
• Highly efficient cooling and energy storage
The proposed design achieves the 20% requirement as
designed in 2011.
There is scope on the building’s roof to triple the PV
allowance, giving a 24% saving.
The building could achieve 30% if we allow the heat
load to increase (increase the infiltration for example)
Health care building Example (Mental Health Unit)
Typically high heating and hot water loads
65% heating
17% hot water
83% of the primary energy (with some ventilation provision)
PV and heat pumps are likely to be the most cost effective
solution and would work for most healthcare buildings
PV
Single
storey
PV
5 storeys
(8%)
Large Health care building Example
(similar results)
Highly air conditioned hospitals would be more difficult but still heat driven.
School Example (Typical School)
85% heating (Primary energy – excluding equipment)
25% Lighting, fans, pumps
High temperature emitters make the use of heat pumps
challenging (without HRV)
PV is the most cost effective method of achieving the renewable
energy obligation in the current energy environment
However, energy that is usable on site is limited to 25%
and when achieving 20%, considerable, unpaid export of energy will
occur if not used for heating etc.
Conclusions:
NZEB Can Be Achieved
Achieving the new standard requires responsible design. It doesn’t happen by default.
Achieving the target requires good design but in most cases should be cost effective when considering running costs.
Some building types are problematic
Some buildings with 24hr loads
Tall, deep plan buildings (low heating loads and high cooling loads)
Energy for processes is excluded but it is not always clear what constitutes a process.
Is an AC system serving a clean room excluded? - Probably
Is an AC system serving a lab excluded? - Probably not
Is an art gallery AC system a process?
There may be some conflict between the NZEB and the Renewable Requirements in the future
Making some buildings notably better than the reference building makes the 20% requirement difficult to achieve.
Making zero heating buildings (that are still actively cooled) makes the target difficult to achieve in some cases.
Chris Croly
Building Services Engineering Director
BDP