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 airtightness 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 11 m3/hr/m2.

Using the appropriate default values, the calculated BER and energy value was E2, 351.94 kWh/m2/yr. When compared to the data on the BER database, this result is very similar to the average rating (E2, 373.21 kWh/m2/yr) for a mid-terraced pre-1945 house.

The small rear extension, built in the mid 1990s, improves the energy rating, though its is limited as the volume of the extension only represents approximately 14% of the total heated volume of the dwelling. Furthermore, insulation standards in the 1990s were poor when compared to those of today. The suspended timber floor in the original dwelling was replaced with a solid floor in the mid 1990s, providing further improvement.

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 6.93 m3/hr/m2 at a 50 Pascal pressure differential. This is a good deal lower than the DEAP default value applied in DEAP assessment 1.

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 the retrofitted secondary glazing and solid ground floor will tend to make a building more airtight, a value like 6.93 m3/hr/m2 is to be expected for a retrofitted, traditionally-built dwelling like this.

The U-value of the brick wall to the front of the house was also measured and was found to be 1.62 W/m2K (+ 13.37% tolerance) which is almost 23% lower than the DEAP default value of 2.1 W/m2K (ref: Chapter 2.3.4 - Case study insights - comparing measured, calc + default U-values of solid walls).

A second DEAP assessment was carried out incorporating the measured level of air tightness and the measured U-value of the front brick wall and resulting in a BER of ‘E1’ and an energy value of 327.39 kWh/m2/yr. This improved energy value is used as the baseline to which the energy efficiency improvements of the minor and major renovation are applied.

DEAP assessment 3 – featuring minor renovation

A third DEAP calculation was carried out, incorporating all the lower-cost improvement measures with minimal heritage impact listed in the table describing Proposed Minor Renovation Project and Heritage Impact. Of these, the measures contributing to an improved BER include upgrading the attic insulation, reducing ventilation heat losses by blocking up the chimneys and installing a chimney damper in one chimney, replacing the old oil boiler with a condensing version and installing demand-controlled mechanical extract ventilation and low-energy lighting throughout. Following these improvements, the BER and energy value improves to C3, 204.52 kWh/m2/yr.

DEAP assessment 4 – featuring major renovation

For the fourth DEAP calculation, the major renovation project works (listed in the table Proposed Major Renovation Project and Heritage Impact) were then applied, including installing internal wall insulation to the front brick façade, external wall insulation to the rear walls, upgrading the timber frame walls of the rear oriel window, upgrading the roof over the bathroom and replacing the windows to the rear of the dwelling. Following these works, just over 90% of the external envelope has been upgraded. To reflect the improvements to the building fabric, a target airtightness level of 1.5m3/hr/m2 has been applied.

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 SEAI’s Home Energy grant scheme, SEAI have 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 3.17 W/Km2 to 1.49 W/Km2, making it suitable for a heat pump installation. Upgrading the building fabric and installing an air to water heat pump improves the BER to an A3, 53.84 kWh/m2/y, improving the energy value by 85%.

Fuel Costs

Information provided by the householder shows that oil costs for 2012 were approximately €703.00.  This compares with a DEAP estimate of €1,955 for the annual oil usage at current SEAI domestic fuel costs. Actual oil costs appear to be just over a third of those estimated by DEAP.

DEAP estimated fuel costs often vary considerably from actual fuel costs for a number of reasons:

• DEAP assumes the living room is heated to 21°C and the remainder of the dwelling is heated to 18°C – the reality is that these temperatures are seldom reached in poorly insulated dwellings.
• 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 carried out with caution. The key data of the building energy assessment provided in the table shows an estimated fuel cost of €2,614 for the building in its current condition at the time of assessing this case study in 2018. This includes the cost of oil 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 as €580. This figure represents a saving of 78%. In reality, the actual fuel bills and savings would depend on occupant use, a factor not accounted for in DEAP.