Nzeb case study esb

NZ

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Case S

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: E

SB

Offic

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Fitzw

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m S

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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

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Imp

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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