Energy

Energy assessment

Areas: Floor areas following works.

Ratios: The heat loss area/floor area ratio indicates the compact envelope of the house – an important factor when considering wall insulation. Similarly, the window area/floor area ratio indicates the windows’ contribution to heat loss. 

Energy rating: BER/DEAP assessments were undertaken before and after the works which give a measure of the improved BER rating of the house. BER ratings are measured on a scale of energy consumption (kWh) per m2 of floor area per year (kWh/m2/yr), which is referred to as the energy value. 

Energy: Heating costs are estimated using energy consumption from DEAP and current fuel prices. Estimated costs can often be much higher than reality as the software assumes both a standardised heating pattern and temperatures throughout the house that may not reflect reality. Similarly, the actual costs can be higher if house owners exceed the standard heating pattern or assumed ventilation rates. 

DEAP assessment 1 – as per standard BER assessor procedure

The first DEAP assessment was carried out using the data collected during an on-site survey combined with the corresponding set of default values, as set out in the DEAP Manual, for existing dwellings.

The DEAP default value for air tightness (applied where an airtightness test has not been carried out) is based on the type of ground floor, the main structure of the dwelling and the percentage of openings, which are draughtproofed. There are two types of ground floor in this dwelling – a suspended timber floor to the front and a solid floor to the rear. In order to select a default air tightness value, only one floor type can be selected. As the solid floor makes up the larger heat loss floor area, the suspended timber floor is disregarded for the default air tightness level, giving a better default air tightness value. Despite this, the DEAP default value for airtightness was estimated to be 11 m3/hr/m2 – worse than the actual tested air permeability rate.

Using the appropriate default values, the calculated BER and energy value is F, 433.22 kWh/m2/yr.  Looking at the data on the BER database, this result is similar to the average rating of (F, 450.87 kWh/m2/yr) for a two-storey, mid-terraced pre-1900 house with similar boiler efficiency (78%) and no building fabric upgrades.

DEAP assessment 2 – featuring measured values

Following the initial BER Survey, an air pressure test was carried out, which gave an air permeability result of 9.02 m3/hr/m2 at a 50 Pascal pressure differential. An air pressure test measures the flow of air through gaps and cracks in the building fabric. This uncontrolled air leakage increases the heat load of the house as warm air is lost or cold draughts enter depending on external air pressure. To put this tested air permeability rate into context, some of the busiest air pressure testers in the country have found 6.0 m3/hr/m2 to be the persistent median value of the total number of buildings they have measured both old or new; the current (2011) Building Regulations require a value of 7.0 m3/hr/m2 for new dwellings; and the 2008 Building Regulation figure was 10.0.

A second DEAP assessment was carried out incorporating the measured level of air tightness resulting in a BER of ‘F’ and energy value of 428.18 kWh/m2/yr. This slightly improved energy value is used as the baseline, to which the energy efficiency improvement of the minor and major renovations are applied.

There are a number of reasons for the poor BER score. The house is very poorly insulated with only a very small amount of insulation in the front attic. The windows to the rear have been upgraded, but the impact of this upgrade which constitutes a small part of the overall heat loss envelope is limited.  There is poor control of space and hot water heating and a low-efficiency boiler. This house also has high air infiltration levels. The air pressure test identified the main leakage points as being the single-glazed timber sash window to the front of the property, the loft hatch and the gaps between the floorboards in the suspended timber floor. All of these problem areas are dealt with in the proposed upgrade works.

Finally, the house has a very small floor area (just under 53 sqm). DEAP calculates the total energy consumption and divides this result by the dwelling floor area to give the BER and energy value. Within the DEAP calculation certain heat losses and gains are calculated based on the floor area and others have a constant contributory factor, which is independent of floor area resulting in a worse BER score for small dwellings.

DEAP assessment 3 – featuring minor renovation

A third DEAP calculation was carried out incorporating all the minor renovations listed above in the table describing Proposed minor renovation project and heritage impact. These works are the lower cost measures with minimal heritage impact and improve the BER to a D2, 273.92 kWh/m2/y – an improvement of just over 40%. The works, providing the biggest impact on the BER score are the boiler and heating control upgrade, draughtproofing (improving the air tightness to an estimated 6.0 m3/h/m2) and attic insulation. The installation of demand controlled mechanical extract ventilation has a negative effect on the BER score, due the electricity usage of the pumps and fans. However, the benefit of DCMEV in terms of indoor air quality and moisture control outweigh any small energy penalties incurred by running the system.

DEAP assessment 4 – featuring major renovation

The final DEAP calculation takes account of the impact of the major renovations detailed above in the table describing Proposed major renovation project and heritage impact, including insulating the front and rear walls, suspended timber floor, and roof to the rear. Also, to reflect the improvements to the building fabric, an air tightness level of 4.5m3/hr/m2 has been estimated. These works reduce the dwelling heat fabric and ventilation loss by 50% when compared to DEAP assessment 2 and improve the dwelling to a C1, 161.98 kWh/m2/yr.

Fuel Costs

Fuel costs as estimated by DEAP often vary considerably from actual fuel costs. There are a number of reasons for this:

• DEAP assumes the living room is heated to 21°C and the remainder of the dwelling is heated to 18°C – in reality, in poorly insulated dwellings these temperatures are seldom reached.
• DEAP also assumes the house is heated from October to May for eight hours per day – in reality, the heating patterns are dependent on occupancy patterns and preferences.
• Domestic hot water demand is based on assumed occupancy rates which are based on floor area.
• Where there is a second room heater in addition to the main space heating system, it is assumed in DEAP that the room heater (an open fire in this case) will supply 10% of the space heat demand – regardless of how often the room heater is used in reality. Often this over-estimates the use of room heaters.

For these reasons, caution must be exercised when using DEAP to estimate fuel costs. The table describing Key data of building energy assessment shows an estimated fuel cost of €1,325 for the building in its current condition. This includes the cost of gas for space and water heating, electricity for lighting, pumps and fans and smokeless fuel for the open fire.

Following the upgrade works, DEAP estimates the total fuel cost for space and water heating, electricity for fans, pumps and lighting and smokeless fuel for the stove as €534. This figure represents a saving of 60%. In reality, the actual fuel bills and savings would depend on occupant use, a factor not accounted for in DEAP.