efficiency measures
Good 3 Average reported measured value for
insulated solid wall
Double glazed windows Small amount of thermal insulation (found in 98 % of houses)
U-value = 1.4 W/m2K U-value = 2.1 W/m2K U-value = 1.0 W/m2K
Good 3 Average reported measured value for insulated solid wall
High performance triple
glazed windows Insulation standard of 0.25 m thickness of insulation
U-value = 0.44 W/m2K U-value = 1.8 W/m2K U-value = 2.1 W/m2K
Very good 4 Building standards level for improved solid wall insulation
U-value = 0.3 W/m2K
1 CIBSE: Chartered Institute of Building Service Engineers. A U-value of 2.1 W/m2K is typically used in SAP (Standard Assessment Procedure) calculations
Figure 5-4 Calculated values of heating energy demand for a range of base level thermal resistance and
improvements. Numbers in square brackets refer to indication of thermal resistance level in Table 5-5, corresponding to wall, window, roof and infiltration standard
The range of values of heating energy consumption before and after intervention demonstrate the wide range of values of savings which could be calculated depending on which assumptions are made for the parameter values selected for the initial state of the building envelope thermal resistance.
For comparison of modelled values against typical values, more in-depth validation is undertaken in section 5.6. Measured gas consumption values for a similar three bedroom property span a range of 21,400 kWh/yr (upper quartile for a pre-1919 house) to 9,000 kWh/yr (lower quartile of house build post 1999) (DECC 2014c). The modelled values range from 11,500 kWh/yr to 27,680 kWh/yr is therefore the right order of magnitude, but values are towards the upper end (especially once a conversion from heat demand to gas consumption is applied as is given greater consideration in section 5.6).
For the purpose of modelling in this project, the level of thermal resistance of each building element will be based on values measured in empirical studies (quoted in literature) rather than the commonly assumed values and building standards. Therefore, for the thermal
0 10,000 20,000 30,000
All poor level of thermal resistance [1-1-1-1]
Some roof insulation [1-1-2-1]
Double glazed windows [1-2-1-1]
Windows and roof at higher base level [1-2-2-1]
Higher level of initial wall and roof insulation [2-1-2-1]
All catagories higher thermal resistance base level [2-2-2-2]
Insulated walls (with single glazing) [3-1-2-3]
Improved wall insulation (with double glazing) [3-2-2-3]
Highly improved wall insulation [4-2-2-3]
Improved wall insulation and roof insulation [3-2-3-3]
Highly improved wall insulation and roof insulation [4-2-3-3]
Improved windows [2-3-2-2]
All catagories have been improved [3-3-3-3]
All catagoried improved (walls higly improved) [4-3-3-3]
Ba se level Wi th im pr ovem en t
transmittance of a solid wall, an un-insulated wall is ascribed a U-value of 1.40 W/(m2K) and an insulated wall is given a U-value of 0.44 W/(m2K). For the roof, a base level prior to additional insulation is given a U-value of 1.00 W/(m2K). For the simulation of additional insulation, a U-value of 0.16 W/(m2K) is used due to a general consensus in the literature and since insulating between rafters in the roof space is more straightforward than other types of insulation. The modelled U-value reductions represent improvements from 'typical' [level 2] to 'good' [level 3] (in reference to Table 5-5). Windows will be double glazed throughout (representing a standard of 'typical' [level 2]).
The construction of other building elements which are not being investigated are taken from standard building constructions in CIBSE guide A (CIBSE 2006a). All building envelope construction elements are described in Table 5-6.
Table 5-6 Wall, roof and window construction used in model Building
element Thermal resistance level Material Thickness (m) (W/(mU-value 2K))
Wall (Solid wall construction)
Pre-insulation (empirical
U-value) Brick Plaster
0.360 0.045
1.40 Typical insulated (internal
wall insulation) Brick Insulation (mineral wool) Plasterboard
0.360 0.065 0.020
0.44
Internal walls Typical construction Plaster Brick Plaster 0.013 0.215 0.013 1.52
Boundary walls Typical construction Plasterboard Brick Plasterboard 0.012 0.220 0.012 1.40 Roof (horizontal base of roof space Pre-insulation (empirical
U-value) Insulation (Mineral wool) Plasterboard
0.032 0.012
1.00 Typical insulated Insulation (Mineral wool)
Plasterboard
0.250 0.012
0.16
Roof tiles Typical construction Tiles 0.02 5.26
Windows Double glazed 2.83
Ground Floor
(solid) Typical construction Plywood Concrete
0.010 0.100
0.86
5.4.2.3 Service control: TRVs and advanced heating controls
In the case of home heating, the way in which the input of final energy is controlled can enable the service of thermal comfort to be delivered more efficiently by reducing waste. If a room is heated whilst unoccupied, no service is being delivered and therefore energy is consumed for no delivered benefit. Conversely, good control can pre-empt the beginning of an occupied period and therefore ensure that the service is being sufficiently delivered as soon as it is required.
Central heating is most commonly controlled using a combination of wall thermostat, programmable timer and thermostatic radiator valves (TRVs) (Munton et al. 2014). A wall thermostat is typically situated in the main living room or hallway to turn the heating system on and off as internal ambient temperature rises and falls. A programmable timer enables a household to control the schedule of heating throughout the day, including setting heating to switch on before the house is occupied to allow for a warm-up period. TRVs allow temperature set-points to be varied between rooms in the house by use of a thermo-responsive valve controlling the flow of water through each radiator. Beyond these common controls, the innovation in wireless control and the availability of more powerful batteries have led manufacturers to develop advanced heating controls that allow space heating to be regulated in individual rooms (Beizaee et al. 2015). Advanced zonal heating controls (AZHCs) make it possible for the set point temperature of rooms to be adjusted on different time-schedules based on a household's occupancy patterns. AZHCs also have the capability to be controlled remotely, for instance from a computer or smart phone, giving a household flexibility to change the heating times daily around their personal agenda. The ownership of heating controls allow for different heating management options as shown in Table 5-7.
Table 5-7 Heating management options enabled by heating controls
Heating management option Heating controls House
thermostat Heating timer Thermostatic Radiator Valves (TRVs) Advanced control – individual room thermostats
Timing of heating controlled by pre-set schedule, no individual
temperature control in rooms X X
Timing of heating controlled by pre-set schedule, rooms set at
constant varied temperature X X X
Heating controlled in each room individually by time and
temperature set-point X
The method of heating control is replicated within the building model through temperature set-point schedules. Heating set-point temperature schedules are created for the present work based on data gained for typical occupancy profiles and typical temperatures of internal zones at different times of day, taken from empirical studies in literature and covered in more detail in section 2.3.3. Six varied heating options have been created based on the availability and use of different types of heating controls. These heating options are detailed in Table 5-8.
Table 5-8 Examples of heating schedules for different heating control options - illustrative
Heating energy demand is calculated for the full range of heating control options exhibited in Table 5-8, and these are presented in Figure 5-5. The calculated energy demand for the most basic control of a single house thermostat is over 30 % higher than any other option, demonstrating the savings achievable for some form of timing control. Manual timing control shows a significantly lower energy demand than programmable timing control demonstrating that technology adoption does not always result in energy savings, but may
Heat Control
Option Description Example of schedule
1
1: House
thermostat Temperature maintained at same temperature throughout
day All rooms
H:
T: 0.00 𝑇𝑜ℎ 24.00 𝑇𝑜ℎ