nZEB office building Ympäristötalo in Helsinki, Finland

REHVA Journal – February 2012

City of Helsinki has taken the exemplary role of the public sector seriously. The latest proof is the Environment Centre building Ympäristötalo completed in last year. It shows the best energy performance of an office building ever built in Finland. Total primary energy use of 85 kWh/(m² a) including small power loads is expected to comply with future nearly zero energy building requirements. The building is also highly cost efficient, nZEB related extra construction cost was only of 3–4%.

Jarek Kurnitski

REHVA Fellow

Sitra, the Finnish Innovation Fund

jarek.kurnitski@sitra.fi

Ympäristötalo, construction year 2011

Technical data

Energy performance

The building has a high quality building envelope, south facades being double facades with integrated PV cells providing effective solar protection at the same time. All the building, except the atrium space, is air-conditioned with effective integrated balanced ventilation and free cooling system with passive and active chilled beams. All the cooling is from boreholes, which water is directly circulated in air handling units and chilled beams. Heating systems is based on district heating and water radiators. Highly significant energy efficiency measures are large air handling units and ductworks enabling low specific fan power, combined with demand controlled ventilation in most of rooms except cellular offices, and effectively controlled lighting. The simulated energy performance is shown in Table 1. On site renewable energy production of 7.1 kWh/(m² a) PV power generation and 10.6 kWh/(m² a) free cooling from boreholes have significant effect on achieved total primary energy value of 85 kWh/(m² a). Typical to nZEB buildings, the highest primary energy component is the small power loads.

Table 1. Simulated energy performance (all values per net floor area).

Compactness and solar shading

The building has a reasonable compact massing and excessive glazed areas are avoided. The main facade to south is accomplished as a double facade in order to provide effective solar shading and to serve as mounting for PV panels. Window area is 23% of the external wall area, but the double main facade still provides an outlook of a glass building from major direction. The double facade is open from bottom and has motorized ventilation openings on the top. In total there are about 30 motorized openings/windows used for the double facade and atrium excess heat removal and some of them are also used for smoke removal. The openings are to be open when needed (manual control from reception) and they will be closed by weather station control, based on wind, rain and temperature, automatically.

Windows have blinds between panes.

Energy supply

The building is connected to Helsinki district heating system. District heating is used for hot water and space heating through central air handling units and hot water radiators.

All cooling need is covered with free cooling from borehole water. The borehole system consists of 25 boreholes each 250 m deep. A simple borehole cooling system with a circulation pump and a water tank serves both the central air handling units and chilled beam units installed in offices and other spaces. Boreholes are sized to provide 15°C supply design temperature (return 20°C) to the water tank at dimensioning conditions (normally the borehole water temperature is lower). Air handling units’ cooling coils and chilled beams network are sized to 16/20°C design flow temperatures from this water tank.

South facade of the building has a double facade with vertical PV panels and some panels are also installed on the roof. The total installed PV power is 60 kW (570 m²) that provides about 17% of electricity use of the building.

PV installation on the double facade to south serving also as an effective solar shading.

Ventilation and air conditioning system

The building has an air-conditioning system with mechanical supply and exhaust ventilation and chilled beams. There are 3 main air handling units and 4 risers with zone dampers for each floor. Separated exhaust fans for toilets are not used and are replaced with a small 0.5 m³/s air handling unit with rotary heat exchanger. The main large air handling units of 2.4, 4.2 and 4.0 m³/s have heat recovery temperature ratios of 80, 79 and 78% respectively. The rest, smaller air handling units have temperature ratios of 80–81%. Ventilation system is balanced so that design supply air flows equal to design extract air flows.

Outdoor air is filtered and heated or cooled in central air handling units and supplied to rooms. Supply air is heated in the central air handling units partly with heat recovered from extract air and partly with heating coils. When cooling is needed, supply air is first cooled in the central air handling units and then cooled further in the chilled beam units.

Air conditioning system with mechanical supply and exhaust ventilation and chilled beams.

Atrium space of the building has no installed cooling and overheating is avoided by opening bottom and top windows. Motorized openable widows are to be open manually when needed and will be closed by weather station control (wind, rain and temperature control) automatically.

Large air handling units and ductworks have been used to achieve as low specific fan power as 1.4–1.6 kW/(m³/s) for offices and similar spaces and 1.8 kW/(m³/s) for VAV air handling unit serving meeting rooms.

Room conditioning solutions

All open-plan and cellular office spaces have room conditioning with active or passive chilled beam units installed in the ceiling, and controlled by room temperature controllers. Air volume flow rate is kept constant (constant pressure CAV). Rooms are heated with hot water radiators controlled by thermostatic radiator valves.

Active chilled beams are used in cellular offices and passive chilled beams in other rooms. Passive chilled beams allow to use cooling also during nights and weekends when ventilation is switched off. This reduces peak cooling loads to 40W/m² that is important in the free cooling system with limited capacity.

Ventilation in the meeting rooms, lobby and workshop areas is controlled by CO₂ and temperature sensors. VAV dampers are used and air flow rates in the meeting rooms are controlled between 0–4 l/(s m²). Office rooms have CAV ventilation of 1.5 l/(s m²). The major part of cooling and heating is supplied by the water systems (beams and radiators respectively).

Active chilled beams and lighting fittings in offices.

Supply air temperature is extract air temperature compensated and is set between 17 to 22°C. The supply air temperature is controlled by adjusting the rotation speed of the regenerative heat exchanger and the water flow control valves of the heating and cooling coils.

Lighting system

Lighting systems uses 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. Lights and chilled beam units have a communication link to building management system (BMS). Outside normal office hours, the BMS sets lights off and lighting demand is controlled by IR motion-sensors.

Key achieved sustainability issues

The best energy performance of an office building ever built in Finland. Total primary energy use of 85 kWh/(m² a) including small power loads is an half of a code requirement of 170 kWh/(m² a) and is expected to comply with future nearly zero energy building requirement.

Very good indoor climate quality according to Finnish Classification of Indoor Environment.

Well controlled construction cost of 2 430 €/m² is roughly a cost for standard office building in Finland, including only 3...4% extra energy performance related cost.