Table 2 Energy efficiency retrofit technology clusters for existing office buildings (self-reported)

1

Internal respiration-type glass curtain wall (C)

Solar wall

Municipal central heating (C)

Lighting from courtyard and side-opened space

2

External respiration-type glass curtain wall (HC)

Natural ventilation system of solar chimney

Boiler renovation (C)

Enlarging the area of daylight opening

3

External thermal insulation of exterior wall

Solar house

Radiator renovation (C)

Light-guided sun-shading system

4

Internal thermal insulation of exterior wall

Solar PV power generation

Single-building heat metering (C)

Prism glass window

5

Multi-layer hollow glass door and window (C)

Hollow glass door and window (HC)

Heat pump technology for underground water source

Combined supply system of cooling, heating, and power

Light pipe

6

Low-E hollow glass door and window (high transparency) (C)

Low-E hollow glass door and window (sun-shading type) (HC)

Independent VAV heat pump-type air conditioning system

Reflector

7

Heat-absorbing glass (HC)

Radiant cooling ceiling

Ventilation from courtyard and side-opened space

8

Adding anteroom (C)

Cold-storage air conditioning system (HC)

9

Increasing airtightness of door and window

Water-water heat pump system (HC)

Air-guiding wall

10

Glass daylighting roof + sunshade

Air-source heat pump system (HC)

Open yard and ventilating tower

11

Planted roof

Night ventilation

12

Impounded roof (HC)

Air conditioner ventilation + natural ventilation

13

Elevated overhead roof (HC)

Air supply from air conditioner + mechanical ventilation + natural ventilation

14

Cold roof system (HC)

Efficient light source

15

Internally/externally insulated roof

Energy efficiency lamp

16

Internal sun shading louver, roller blind, and curtain

Control device

17

Horizontal sunshade + vertical sunshade

Intelligent lighting control system

18

Integrated sunshade

19

Deciduous tree

20

Liana