Riga Technical UniversityInstitute 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 - 662m2 Volume – 14214m3 Height – 6 storeys, 24m

Envelope/volume ratio (Net) – 0.24m2/m3 Envelope/volume ratio (Gross) – 0.25m2/m3 Window/envelope ratio – 32%

Solar protection – standard glazing + shading devices

Cooling technique – Mechanical cooling + night cooling

The lowest possible area/volume ratioCan 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 - 0.62;•Tsolar - 0.54;•Tvisible - 0.8;

Description of external constructions:

•External wall - 0.14W/m²K;•Roof - 0.12Wm²K;•External floor - 0.33W/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

17 8 -9 -53%

Peak load, kW 247 217 -30 -12%

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

17 12 -5 -29%

Peak load, kW 247 197 -50 -20%

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

17 8 12 4 -13 -76%

Peak load, kW 247 217 197 138 -109 -44%

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.

Thank you for your attention!