1. A Closer Look at Energy Demands: Quantification and Characterisation

2. Why is demand data important? having information on likely energy demands is a key requirement of a low energy building deisgn we can assess if design criteria have been met allows us to target demand reduction measures … or we can size low carbon energy supply equipment

3. Aggregate Energy Demand the simplest way to describe the energy consumption of a building is to provide an aggregate value is consumption over a time period (a year) lumps all energy demands together (heat/electrical) often expressed in kWh/m 2 … or as a non-dimensional rating (e.g. SAP) …useful as a performance metric – not that useful for design

4. Disaggregating by Load Type dissaggregation gives us more detail e.g. looking at what the energy was used for useful for targeting demand reduction measures … or to select energy supply technologies

5. Disaggregating by Load Type

6. Temporal Characteristics load data can be disaggregated in different ways: -by type -spatially (by location) -temporally (by time)

7. Temporal Characteristics

8. Calculating Energy Demands we’ll look at how we can quantify and characterise each of the major energy loads in turn

9. Calculating Heating/Cooling Demands we are spoiled for choice when it comes to determining space heating or cooling demands simplified methods: -Standard Assessment Procedure SAP * -degree-day method** (daily or monthly heating/cooling demands) -basic UA calculation more comprehensive methods: -building simulation (hourly  minutely heating or cooling energy demand) * produces a rating not a value, **does not adequately account for internal and solar gains

10. Climate Data the starting point for a heat load calculation is climate data this could be as simple as an average annual external air temperature or as detailed as hourly readings of temperature, solar radiation, wind speed and wind direction

11. Calculating Heating/Cooling Demands SAP is used more for compliance checking (with building regulations) than as a design tool gives an energy rating score (1-100) using a ‘tick-list’ based on the building design

12. degree day/U-value methods are energy balance based DD assumes that is ext. air temp > 15.5 o C there will be no heating load the assumption is that when the ext air temp reaches this point internal heat gains in the building will keep the temperature ~ 18.5 o C does not adequately account for equipment gains … or solar gains (increasingly important in well-insulated dwellings) doesn’t account for thermal dynamics caused by building fabric Calculating Heating/Cooling Demands

13. for each day (or longer period) calculate the accumulated degree days calculate the associated energy demand (kWh) Calculating Heating/Cooling Demands

14. a basic UA calculation can be uses to produce annual daily or hourly demand data the calculation could be performed once for T  equal to an annual average to give an annual energy consumption … or 8760 times with hourly external temperature readings and temperature set points to give hourly space heating demands Calculating Heating/Cooling Demands

15. … again, does not adequately account for equipment gains or solar gains doesn’t account for thermal dynamics caused by building fabric Calculating Heating/Cooling Demands Q f - fabric Q i - infiltration Q s - solar Q g - gains Q h - heat

16. the most robust approach is to use a simulation tool to calculate heat load -building is typically decomposed into hundreds of volumes -an energy balance is set up for each ‘volume’ which includes fabric energy storage -internal heat gains, solar gains calculated using climate, geometric and schedule information -solution of all of the individual energy balance equations gives the heat flows and temperatures throughout a building typically at hourly or sub hourly time intervals -computer and software required and usually does more than calculate heat demand data Calculating Heating/Cooling Demands

17. typical output is as follows: Calculating Heating/Cooling Demands

18. Calculating Heat Gains to effectively calculate heating/cooling loads we need to calculate the other energy inputs (solar and internal heat gains) –solar gain is typically calculated within building simulation tools as part of the heat gain calculation or can be pre-calculated using climate data, geometric data and glazing data –internal heat gains (people and equipment) are typically prescribed and are a “boundary condition” for the heating/cooling load calculation

19. Calculating Heat Gains the basis for these is typically a prescribed schedule detailing: when people are ‘active’ and when equipment is functioning typically occupancy ‘profiles’ are developed these are then used with heat gain data to calculate time series heat gains, that are used as boundary conditions for modelling time-series performance

20. Calculating Heat Gains data is available for people and equipment (for example):

22. using occupancy/equipment profiles and heat gain data enables a time-series heat gain profile to be developed Calculating Heat Gains

23. Calculating Electrical Demand the electrical demand profile can be derived from the heat gain profile for electrical consuming equipment or vice versa can assume that 100% of the electrical demand is eventually degraded to heat a few exceptions e.g. lighting with in built extract also it is possible to simulate the operation of daylight controlled lighting using a simulation tool (e.g. ESP-r) or some lighting design tools (e.g. DIALUX) there are also free tools to generate electrical profiles

24. Calculating Electrical Demand the characteristics of electrical demand can be significantly affected by time-averaging generally the higher the time resolution the more realistic the electrical demand profile

25. Calculating Hot Water Demand as with occupant and equipment gains, hot water demands are typically calculated using a pre-defined draw-schedule this indicates the total draw being taken from a storage tank or needs to be supplied from a device

26. Calculating Hot Water Demand again these are highly intermittent and significantly affected by averaging the resulting time-series heat demand (W) can be calculated if the hot water supply temperature and the feed water inlet temperature are known or assumed

27. Calculating Resulting Emissions calculation of emissions associated with energy use require the desegregation (by type) of energy demands …and carbon emissions rates (c x ) for the different fuel types the carbon emissions are determined by multiplying the energy consumption over the period analysed by the appropriate rate: