Riga Technical University Institute of Heat, Gas and Water technology OFFICE BUILDING NIGHT COOLING POTENTIAL IN BALTIC REGION RENARS MILLERS, ALEKSANDRS ZAJACS, ARTA USELONOKA.

General information: Location – 56.97° N, 24.07° E(Riga), Site– outside city centre, surrounding agglomeration 2-4 storey buildings Model ground area - 662m 2 Volume – 14214m 3 Height – 6 storeys, 24m Envelope/volume ratio (Net) – 0.24m 2 /m 3 Envelope/volume ratio (Gross) – 0.25m 2 /m 3 Window/envelope ratio – 32% Solar protection – standard glazing + shading devices Cooling technique – Mechanical cooling + night cooling

The lowest possible area/volume ratio Can be expressed as - 3/r A/V ratio of a sphere with the same volume – 0.2 Starting point – the form Sphere If h=D then A/V ratio can be expressed as - 3/r A/V ratio of a sphere with the same volume – 0.22 Cylinder A/V ratio – 0.25

Window description: U - value - 1.2W/m²K; G - value ; Tsolar ; Tvisible - 0.8; Description of external constructions: External wall W/m²K; Roof Wm²K; External floor W/m²K; Air tightness - 0.6ACH at 50Pa; Concrete building body and slabs help to achieve greater thermal mass for accumulating heat during occupied hours. Building envelope

Night cooling – predicted air movement Predicted air exchange rate – 5 ACH

Simulated air exchange rate – 7.9 ACH, Indoor/Outdoor temperature difference – 10K, No wind present Night cooling – simulated air movement

The benefits of night cooling Mechanical cooling Mechanical cooling + night cooling Absolute reduction Relative reduction Annual energy consumption for cooling, kWh/m² % Peak load, kW %

Simple shading design No external shading devices With external shading devices

Mechanical cooling Mechanical cooling + shading devices Absolute reduction Relative reduction Annual energy consumption for cooling, kWh/m² % Peak load, kW % Benefits of shading devices

Heat balance of typical room on the south side No shading, no night cooling Shading, night cooling

Shading devices in combination with night cooling as passive cooling approach Mechanical cooling Mechanical cooling + night cooling Mechanical cooling + shading devices Mechanical cooling + shading devices + night cooling Absolute reduction Relative reduction Annual energy consumption for cooling, kWh/m² % Peak load, kW % Reduction from night cooling – 30kW Reduction from shading devices – 50kW 80kW

Conclusions: Stack effect can boost air exchange rate during night cooling in multi- storey building Night cooling in this case is more effective for reducing energy consumption – 53% Shading devices are more effective to reduce peak load – 20% Significant reduction of pike load – 44% can be achieved when using both – night cooling and shading design in combination.

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