kurnitski rehva aicarr-seminar-mce-28.03.2012

Federation of European Heating, Ventilation and Air-conditioning Associations

nZEB Buildings: experiences and

case studies from Central and North

Europe

Jarek Kurnitski

SITRA

[email protected]

REHVA – AICARR Seminar on

Zero Energy Buildings

Milan, 28 March 2012

mailto:[email protected]

© Sitra

nZEB buildings

• Many pilot projects across Europe which may be called as nZEB buildings

• Variation in the definitions and performance levels

• Primary energy (simulated) typically between 50-100 kWh/(m2 a) if all energy use included (plug loads/user electricity incl.)

• Some buildings with measured data

• Buildings may be extremely complicated which may have implications in operation and maintenance

• Simple and reliable solutions based on high performance components and careful system design another nZEB trend

28.3.2012 Jarek Kurnitski

© Sitra

nZEB case studies

• nZEB office buildings in France, Netherlands, Switzerland and Finland

• Reported in REHVA Journal (3/2011 and 2/2012)


© Sitra

nZEB case studies – presentation outline

• Two buildings in more detail

- One from Central Europe, another North Europe

- Some technical concepts similar – suit for both climate

- Some different – depending on climate

- Simulated and measured energy performance

- nZEB extra cost

• Some key technical concepts based on nother buildings

• Can common features of nZEB office buildings be identified?

• Performance specification recommendations for nZEB



System boundary – REHVA nZEB definition

• Electricity use of cooling, ventilation, lighting and appliances is 39.8 kWh/(m2 a)

• Solar electricity of 15.0 kWh/(m2 a) reduces the net delivered electricity to 24.8 kWh/(m2 a)

• Net delivered fuel energy (caloric value of delivered natural gas) is 4.2 kWh/(m2 a) and primary

energy is 66 kWh/(m2 a)

System boundary of delivered energy

3.8 heating

11.9 cooling

10.0 lighting

BUILDING TECHNICAL SYSTEMS

15.0 PV electricity,from which 6.0 used in the building and 9.0 exported

Fuel 4.2

Electricity 33.8

Solar and internal heat gains/loads

Heat exchange through the building envelope

NET ENERGY NEED (47.2 kWh/(m2 a))

DELIVERED ENERGYBoiler3.8/0.9 = 4.2

Free cooling 4.0/10 = 0.4 Compressor cooling 7.9/3.5 = 2.3

Lighting 10.0

Ventilation 5.6

Appliances 21.5

Primary energy: 4.2*1.0 + (33.8-9.0)*2.5 = 66 kWh/(m2 a)

EXPORTED ENERGY

System boundary of net delivered energy

Ne

t de

live

red

en

erg

y

Electricity 9.0

21.5 appliances

(Sum of electricity 39.8)

21,5

10

3,2

0,61,1

10,8

NET ENERGY NEED (47.2 kWh/(m2 a))

Appliances (users')Lighting

Space

heatingHeating of air in AHUCooling in room unitsCooling of air in AHU

© Sitra

Paris, Elithis Tower (Hernandez REHVA Journal 3/2011)

© Sitra

Key solutions

• Rounded shape (-10% envelope reduction) + external solar shading shield

• Mechanical balanced ventilation with heat recovery

• Room conditioning with chilled beams

• Night ventilative cooling with mechanical exhaust ventilation from atrium

• Adiabatic + compressor cooling

• Large windows for max daylight, 2 W/m2 installed lighting power + task lighting, occupancy and daylight control


© Sitra

Mechanical ventilation + ventilative cooling


Three operation modes:

1. In the heating season the heat recovery ventilation, i.e. air handling units are operated.

2. Ventilative cooling: boost with façade intakes and low pressure atrium exhaust fans. Used in midseasons, when air handling units are operated together with atrium low pressure exhaust fans.

3. Night time ventilative cooling. Air handling units are stopped and only atrium low pressure fans are operated.

Façade intake

© Sitra

Simulated and measured energy performance

• Office appliances are the major component in the energy balance…


© Sitra

Helsinki, Environmental Centre Ympäristötalo (Kurnitski REHVA Journal 2/2012)

© Sitra

General data

• Gross floor area 6791 m2

• Construction cost:

- 16.5 M€ (2430 €/m2)

• nZEB extra cost:

- 0.5-0.7 M€

- 3-4% of construction cost


© Sitra

Key solutions

• Compact massing

• Window to wall ratio 23 %

• South facing double facade with integrated PV (60 kW/570 m2 providing 17% of electricity use)

• District heating

• Air conditioning with balanced ventilation, heat recovery and chilled beams

• Cooling is 100% free cooling from boreholes: - 25 boreholes each 250 m depth

- 15/20C cooling water dimensioning for AHUs and chilled beams


© Sitra

Key solutions • Large mechanical rooms on the top floor and low pressure ductwork

• Specific fan power of main AHUs 1.4…1.6 kW/(m3/s)

• Heat recovery (wheels) temperature ratio 78…80 %


© Sitra

Integrated ventilation and AC with free cooling

• CAV for cellular and open plan offices, DCV for other rooms

• Active chilled beams in offices and passive chilled beams for other rooms for 24 h cooling (max cooling need 40 W/m2)

Air handling unit

Chilled beam

ME TE

TE

TE

TC

TC

TC

TE

a)

Supply

Return

District heat substation

a)

Cooling water from boreholes

Thermostat

Room

controller

Supply

Return

Room


© Sitra

Heat recovery from toilets – no separated exhausts

• Separated exhaust fans replaced with a small 0.5 m³/s air handling unit with rotary heat exchanger

• Supply air to toilets, heat recovery of 80%


© Sitra

Room conditioning and lighting

• Active chilled beams (CAV) in offices

• Lighting fittings of T5 fluorescent lamps with 7 W/m² installed power.

• Daylight, occupancy and time control is used in larger rooms, and occupancy and time control in cellular offices


© Sitra

Energy performance (simulated)

Major differences compared to Central Europe:

• much more heating (almost by factor 10)

• only slightly less cooling

• more lighting electricity


Net energy Delivered Energy Primary

need energy carrier energy

kWh/(m2 a) kWh/(m2 a) factor, - kWh/(m2 a)

Space and ventilation heating 26,6 32,2 0,7 22,6

Hot water heating 4,7 6,1 0,7 4,3

Cooling 10,6 0,3 1,7 0,5

Fans and pumps 9,4 9,4 1,7 16,0

Lighting 12,5 12,5 1,7 21,3

Appliances (plug loads) 19,3 19,3 1,7 32,7

PV -7,1 1,7 -12,0

Total 83 73 85

© Sitra

Simple or complex ventilation systems?

• Hybrid systems tend to be highly complicated (many actuators + complicated control) or are to be controlled by user – simulations provide often optimistic results compared to real operation

• Mechanical systems centralized (as in two case studies) or decentralized

• Centralized systems may be complex or not


© Sitra

Example of decentralized ventilation (Achermann, IUCN building, REHVA J 3/2011)


• Air intakes from facade, a filter unit, a fan and a heating/cooling coil

• CO2 sensor located at the exhaust damper integrated into a panel mounted on the ceiling

• No supply air ductwork

© Sitra

Constant pressure nZEB compliant simple ventilation

(Gräslund REHVA Journal 3/2011)

• 1-2 step larger ducts and AHUs

• No need for silencers and most of dampers



nZEB solutions: Natural lighting and solar shading, (Scartezzini and Lamy REHVA AM 2011)

3.5 W/m2 installed lighting power achieved!


nZEB solutions: Solar fired absorption chiller (Virta et al. REHVA GB 16 HVAC in sustainable office buildings)

• An example of a free cooling solution – many possible solutions

• The solar fired absorption chiller operates with hot water from

the roof mounted concentrating solar collector and the wall

mounted coil solar collectors

© Sitra

nZEB case studies: common solutions

• nZEB = demand reduction + effective systems + on site renewables

• Energy sources used: heat pumps, DH, bio-CHP, solar PV and thermal

• Heat recovery ventilation, often demand controlled, by centralized or decentralized systems sometimes combined with natural stack effect ventilation for ventilative cooling purposes

• Free cooling solutions combined with mechanical cooling via boreholes, water to water HP, evaporative or ventilative cooling etc.

• Optimized building envelope and effective external solar protection

• Utilization of natural light + effective demand controlled lighting

• High efficiency heat recovery and low specific fan power, CO2, presence and temperature control typical in nZEB

• Water based distribution systems and VRV heat pumps

• Utilization of thermal mass and other passive measures

• Office appliances have become major component in energy balance…


© Sitra

Key performance specification for nZEB (Virta et al. REHVA GB 16 HVAC in sustainable office buildings)

• Some indicative values for key low and nZEB energy design criteria in cold and temperate climates


Unit Low energy Nearly zero energy

SFP of air handling unit kW/m3/s < 2.0 < 1.5

Heat recovery efficiency % > 60 > 80

Demand controlled ventilation meeting rooms all spaces

Installed lighting power W/m2 < 10 < 5

Lighting control time, daylight time, daylight, occupancy

U-value of window W/K,m2 < 1.2 < 1.0

g-value of window < 0.7 adaptable (seasons)

Solar shading yes automated

Infiltration (q50) m3/h,m2 < 1.5 < 0.6

Share of renewable energy % > 10 >20

© Sitra

Central Europe vs. North Europe

• Large windows for max daylight to save lighting electricity

• Moderate insulation (Uwindow=1.1 , Uwall=0.30)

• More cooling need than heating need

• External solar shading

• “Glass” buildings with external shading possible

• Free cooling combined with compressor cooling or solar cooling

• Water based distribution system for cooling (or VRV)

• Heat recovery ventilation

• Demand controlled ventilation and lighting

• PV panels

• Small windows for lowest acceptable average daylight factor

• Highly insulated envelope (Uwindow =0.6…0.8, Uwall=0,15)

• Slightly less cooling but a lot of heating

• External shading for low solar angle

• Double façade to be used for “glass” buildings

• 100% free cooling possible with borehole water

• Water based distribution systems for heating and cooling (or VRV)

• Heat recovery ventilation

• Demand controlled ventilation and lighting

• PV panels


© Sitra

Experience from nZEB design process

• Energy simulations needed in very early stage to compare massing alternatives (starting from scoping)

• Reserving enough space for mechanical rooms and risers – 1-2 step larger AHUs and ductwork – this space may be difficult to find in a later stage

• Simulations of a typical floor often enough for decision making of basic solutions (concept stage)

• Facades to be optimized (concept stage) for a relevant combination of daylight, solar protection cooling and heating needs

• To achieve targets, careful verification and commissioning needed

• Sometimes official monthly based calculated methods may provide too optimistic results not achieved in practice


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