Energy-saving Analysis Technology of Guolian Green Technology-Guolian Green Technology(Wuxi) Joint Stock Co., Ltd.

Energy-saving Analysis Technology of Guolian Green Technology

The building energy conservation analyzing technology commonly used by Guolian Green Technology mainly includes the following two: Building thermal energy model and CFD (computational fluid dynamics). The building thermal energy model is mainly used for accurate analysis of dynamic load of buildings. CFD technology is mainly used for flow and heat transfer analysis of building spaces. Accurate analysis of dynamic load of building forms the foundation of building energy conservation, and is of great significance of the building energy conservation.

Building Thermal Energy Model

Difference between building thermal energy model and traditional computing method

It is a calculation model used to study the dynamic cold, heat and humidity balance needed for the building to sustain a certain thermal and humid environment, and is an indispensible tool to realize building energy conservation, passive building design and green building. Building thermal energy model differs from traditional computing method in the following ways:

Building thermal energy model calculates the all-year hourly load rather than only design load;
Building thermal energy model uses typical all-year meteorological data rather than designed indoor and outdoor parameters;
Building thermal energy model takes impact of plane and façade arrangement on load into consideration;
Building thermal energy model takes impact of surrounding buildings on calculation of building load into consideration;
Building thermal energy model takes impact of using mode of the building on load into consideration.

Composition of Building Thermal Energy Model

The building thermal energy model is made up of the following parts:

Yearly Meteorological Model
Multi-body and Plane Arrangement of the Building
Parameter of Building Maintenance Structure
HVAC Equipment and Control
Lighting and Control
Use condition of the building
Hot Water Supply System

Fig. 1 shows the building thermal energy model – building model. It includes the orientation, direction, surrounding buildings and plane façade arrangement of the building, and other building layout factors that pose an impact on A/C load of the building.

Fig. 2 (left) shows the yearly dry-bulb temperature change of Beijing. Fig. 2 (right) shows the yearly relative humidity change of Beijing.

Fig. 3 (left) shows the yearly change of direct solar radiation intensity of Beijing. Fig. 3 (right) shows the yearly change of scattering solar radiation intensity of Beijing. The building thermal energy model calculates the cooling and heating load of A/C system based on those hourly meteorological data.

Necessity of Accurate Analysis of A/C Load

Equipment selection in the A/C system design is based on basic design working conditions rather than operation working conditions. However, in practice, due to constant change of seasons, weather, occupancy rate and business activities, the energy consumption load is also changing. In most of the time, the actual load is below the design load. Fig. 4 shows the yearly cooling load change of a building.

Fig. 4 Dynamic Change of A/C Cooling Load of a Building

If we put the cooling loads shown in Fig. 4 in a descending order, we could get the cooling load distribution diagram as shown in Fig. 5.

Load Rang e (kW)	Duration (hours)
3000-4233	275
2000-2999	858
1000-1999	1327
Less Than 1,000	1929

Fig. 5 Duration of Different Loads of a Certain Building

It can be seen that the duration of design load of a building is rather short. In most of the times, the load value is much lower than the design load.In order to improve the building energy conservation performance, quantitative calculation and study of the hourly load and yearly load of the building are necessary.

Comparison Between Load Prediction By Building Thermal Energy Model and Measurements

Fig. 6 shows the comparison between the monthly A/C cooling load model and measurements of a super high-rise hotel in Beijing. It should be noted that the A/C load of a building is subject to impact of various factors, including meteorological parameters, maintenance structure parameters and using mode of the building. These add up to make it rather difficult to accurately predict the A/C load of the building. However, through careful construction of the building model and detailed analysis of the operation law of the hotel, we found that the monthly A/C load model of the hotel was actually in accordance with the measurements. Furthermore, through analysis of the monthly A/C load of the office building, the same conclusion was drawn. This indicates that as long as the thermal energy model of the building is constructed in a scientific manner, such model would be of great guiding significance for energy conserving transformation and operation of the building.

Building energy model is of even greater significance for large transportation hubs (such as airport, high-speed railway station and metro stations), hospitals, convention and exhibition centers and other large scale buildings with complicated architectural structure, mass visitor flow and insufficient operation data.

Internal and External Air Flow and Heat Transfer Analysis of the Building

Computational fluid dynamics (CFD) is a branch of fluid dynamics. It uses numerical calculation method to solve fluid flow related issues.CFD is widely used in sectors such as aviation, aerospace, automobiles, energy and environment protection. The use of CFD technology in the building sector has been increasing in recent years. It is of special meaning to apply CFD technology to architectural design. The flow and heat transfer issues involved in architectural design are quite complicated, and are beyond the calculating capacity of traditional methods. The experimental method is time-consuming and expensive. As such, it is not considered in design .
CFD technology could solve this problem effectively.

CFD Technology can be used in the following areas:

Analysis and calculation of wind environment at the pedestrian level;
Natural ventilation with actions of wind force and buoyancy both taken into consideration;
Exhaust and ventilation;
IT and data center design;
Air flow calculation of large spaces;
Optimization of HVAC equipment

Design of Terminal A/C System
Natural Ventilation Design of the Building
Design of Data Center
Thermal and Humid Environment Design of Large Spaces

Fig. 7 Application of CFD Technology in Building Energy Conservation and Environment Design