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.

Using the appropriate default values, the calculated BER and energy value was G, 698.65 kWh/m2/yr. Looking at the data on the BER database, this result is a lot worse than the average rating (G, 499.67 kWh/m2/yr) for a mid-terraced pre-1900 house.

DEAP assessment 2 – featuring measured values

Following the initial BER Survey, an airtightness test was carried out, which gave an air permeability result of 8.85 m3/hr/m2 at a 50 Pascal pressure differential. The air tightness test measures the flow of air through gaps and cracks in the building fabric. This uncontrolled air leakage increases the amount of heat loss as warm air in the dwelling leaks out and is replaced with the colder air from outside. To put this tested air permeability rate into context, the current (2011) Building Regulation air tightness requirement for new dwellings is 7m3/hr/m2 and in 2008, the Building Regulation requirement was 10 m3/hr/m2.

The DEAP default value for air tightness is estimated based on the type of ground floor, the main structure of the dwelling and the percentage of openings which are draughtproofed. From the information collected during the survey, the DEAP default value for airtightness was estimated to be 13.4 m3/hr/m2 – much worse than the actual tested air permeability rate. This property has an unsealed suspended timber floor and a low level of draughtproofing (67%) – resulting in a poor default level of air tightness. The DEAP default airtightness value is greatly overestimating air infiltration rates.

In addition to measuring the air tightness of the dwelling, the U-value of the front masonry wall was measured and was found to be 2.83 W/m2K (-13.20%). This measured value is worse than the DEAP default value for a masonry wall of 2.1 W/m2K.

A second DEAP assessment was carried out incorporating the actual measured level of air tightness and the U-value measurement and the resulting BER and energy value was G, 710.75 kWh/m2/yr. This energy value, using measured values, where available, was used as the baseline, from which the improvement effects of the proposed works were applied.

The energy performance of this dwelling is extremely poor. This mid-terraced, single-storey dwelling, is considered (within DEAP conventions) to be inadequately heated. The dwelling has an open fire that alone would not be capable of heating the house to the DEAP assumed temperatures of 18 - 21⁰C. Thus, for the DEAP assessment, electric room heaters are assumed to heat the dwelling to comfort temperatures. In addition to the poor space heating and lack of heating controls, there are a number of additional factors contributing to the poor energy rating:

• A high total heat loss element area / floor area ratio (2.85). This figure is much higher than the average of 1.97 for pre-1945 mid-terraced dwellings. This is due to the fact that the dwelling is single storey with a protruding rear extension, thus increasing the exposed heat loss surfaces.
• The small floor area (42.42 sqm) – DEAP calculates the total energy consumption and divides this result by the dwelling floor area to give the BER and energy value. However, in the DEAP calculation, certain heat losses and gains are calculated based on the floor area and others have a constant contributory factor independent of floor area. Therefore, in DEAP, if you have two houses with different floor areas, built to the same proportions, with the same building fabric, heating system and services, the house with the smaller floor area will always have a worse BER result than the larger house.
• High Infiltration (air leakage) levels – The main leakages located were the windows, particularly the front door, gaps and cracks in the walls and around the fireplace and under the floor – although given that it is a suspended timber floor with open ventilators, the levels were lower than might have been expected.
• Poor insulation levels – Currently, there is no insulation in the original house or in the extension and the original windows are single glazed.

DEAP assessment 3 – featuring minor renovation

Due to the extremely poor condition of the existing fabric of the building, it was not considered appropriate to simply apply minor upgrade works.

DEAP assessment 4 – featuring major renovation

For this final DEAP calculation, the major renovation project works were applied, including internal wall insulation, new floor, insulated ceilings, triple glazing, new front door, and airtightness measures to achieve a target airtightness of 1.0 m3/h/m2.

This fabric-first approach reduces the fabric and ventilation losses by approximately 80%. The heat-loss indicator (HLI), calculated in DEAP, is the dwelling’s total fabric and ventilation heat loss per sqm. of floor area of the dwelling. As part of the SEAI Home Energy grant scheme, SEAI has set a target HLI of less than 2.0 W/Km2 as an indicator of suitability for a heat pump installation. This is to ensure that the dwelling’s heat loss is sufficiently low for the heat pump to operate efficiently. The improvement works to this house have reduced the heat loss indicator (HLI) from 6.11 W/Km2 to 1.26 W/Km2. To complete the upgrade, a Nilan Compact P ventilation and heating system will be installed to provide ventilation, heat recovery and domestic hot water.

Upgrading the building fabric and installing the Compact P system improves the BER to an A3, 62.30 kWh/m2/y, improving the energy value by 90%.

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 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, using DEAP to estimate fuel costs must be done with caution. The key data of the building energy assessment provided in the table shows an estimated fuel cost of €2,482 for the building in its current condition. This includes the cost of electricity and smokeless solid fuel for space and water heating, electricity for lighting, pumps and fans.

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 €251. This figure represents a saving of 90%. In reality, the actual fuel bills and savings would depend on occupant use, a factor not accounted for in DEAP.