• Energy Demand

    - Data Collection

    - Data Estimation

         - Space Heating

      - Hot Water Use

      - Electricity

  - Data Analysis

• Renewable Potential

• Home
• Project Overview
• Opportunities
• Methodology
• Case Study
• Conclusions
• Team Members

Methodology for Determining the Energy Demand

The method for determining energy demand in rural locations can be broken down into three constituent parts: Data Collection, Data Estimation and Data analysis. We have developed a series of flowcharts for determining and collating the energy demand; from which a better understanding of the energy usage can be obtained. The flowcharts are primarily based on CIBSE preliminary audits.

Data Estimation                            

 

Figure 1. Data Estimation Flowchart

 

If monthly and quarterly invoices are unavailable then the energy consumption must be estimated. The overall energy consumption is broken down into three parts: Space Heating, Hot water Use and Electricity.

 

Space Heating

The space heating requirement is determined by undertaking an energy balance for the building of interest. An overall energy balance takes into account Heat Losses (through the building fabric and by ventilation), Solar Heat Gains (through windows) and Casual Heat Gains (from people and equipment):

Therefore,

 

Heat Losses

Buildings in rural locations are generally more exposed than those in urban, sheltered environments. Therefore, design heat losses in rural locations are relatively higher than those in urban areas. Heat is lost through the building fabric and by ventilation.

The fabric heat loss from a building is calculated using the following formula:

Where,

Q_F = Rate of Fabric Heat Loss (W)
U = Overall Heat Transfer Coefficient of the element considered (W/m²K)
A = Total Area of that element (m²)
ΔT = Temperature Difference between inside and outside environment (^oC)

Ventilation heat losses are calculated by:

Where,

Q_V = Rate of Ventilation Heat Loss (W)
N = Number of Complete Air Changes per Hour (ach)
V = Volume of indoor space (m³)
ΔT = Temperature Difference between inside and outside environment (^oC)

Heat Gains

In a temperate climate such as the UK, overall heat gains are generally less than the overall heat losses, but can still provide useful energy savings. Heat Gains are considered under two categories: solar heat gains from the sun and casual heat gains from occupants and electrical equipment in the building.

Solar Heat gains are calculated using the ASHRAE method, from the ASHRAE Fundamentals Handbook:

Where,

Q_S = Solar Heat Gain (W)
A = Area of building element considered (m²)
SC = Shading Coefficient
SHG = Solar Heat Gain Factor (W/m²)
CLF = Cooling Load Factor

These values can be obtained for various building fabrics, latitudes and orientations from Chapters 26 and 27 in the ASHRAE Fundamentals Handbook.

Casual Heat Gains depend upon occupancy levels and activity, and the amount of equipment and its frequency of use. For an indoor temperature of 20 ^oC, typical heat emissions from people are as follows:

Table 1. Heat Emissions from People

For electrical equipment, lighting and gas cookers, individual power ratings (W) will indicate typical heat emissions.

Where,

Q_C = Casual Heat Gain (W)
Q_P = Heat Gains from People (W)
Q_E = Heat Gains from Equipment (W)

Hot Water Use

The hot water heat requirement can be determined from the hot water consumption according to the following equation:

Where,

Q_HW = Hot Water Heat Requirement (Wh)
V_HW = Average Hot Water Consumption (l or kg)
c_W = Specific Heat Capacity of Water (Wh/kgK)
ΔØ= Temperature Difference between Hot and Cold Water (K)

Accurate estimations of hot water consumption are difficult to make as individual differences are enormous. It is therefore important to estimate hot water consumption on a case by case basis. Average values for hot water consumption are as follows:

Table 2. Average Hot Water Consumption

                                                                           (pppd) = per person per day

Source: DGS, 2005

Depending on the fittings in the household, the following average consumption values per person per day can be calculated:

                                 Table 3. Average Hot Water Consumption Values Per Person Per Day

Source: DGS, 2005

 

Electricity

Electricity consumption can be calculated by obtaining the power rating of all electrical appliances and lighting and multiplying this by their frequency of use:

Where,

Q_E = Electrical Power Consumption (kWh)
P_E = Power Rating of appliance (kW)
t = Number of hours for which appliance is used

Some typical power ratings for electrical appliances are as follows:

Table 4. Average Power Rating of Electrical Appliances

Source: www.energysavers.gov