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 for existing dwellings as set out in the DEAP Manual. Using the appropriate default values, the calculated BER and energy value was G, 458.50 kWh/m2/yr. This result is lower than that achieved by a typical mid-terraced, mass concrete 1940s house in original condition, which achieved a BER and energy value of F, 398.00 kWh/m2/yr as analysed in the 2012 TABULA study on the energy performance of typical Irish dwellings.

DEAP assessment 2 – featuring measured values

Following the initial BER Survey, an airtightness test was carried out, which gave an air permeability result of 4.28 m3/hr/m2 at a 50 Pascal pressure differential. The air tightness test measures the uncontrolled air leakage through gaps and cracks in the building fabric. To put this tested air permeability rate into context, this house exceeds the current Building Regulation airtightness requirement for new dwellings of 7 m3/hr/m2.

The airtightness test identified the main leakage points as being the letterbox in the front door, the gap between the front and rear door frames and doors and the loft hatch. The air leakage around the doors alone increased the total air leakage rate by 24%. These main air leakage points can be greatly improved by installing simple draughtproofing measures.

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 – significantly worse (162 %) than the actual tested air permeability rate.

In addition to measuring the airtightness level in the house, the U-value of the solid concrete wall was measured and found to be 3.37 W/m2K. This is significantly worse than the DEAP default U-value of 2.2 W/m2K for a 1940s solid mass concrete wall.

The second DEAP assessment includes the actual measured values for the wall U-value and air tightness and the resulting BER and energy value was G, 500.88 kWh/m2/yr –worse than the default DEAP assessment result. This energy value, using measured values, where available, was used as the baseline, from which the improvement effects of the proposed works were applied.

This is a compact, mid-terraced dwelling. The total heat loss element area of this house (exposed floors, walls, roof, windows, etc.) is 179% of the floor area. This figure is lower than the average of 213% for pre-1945 dwellings due to it being mid terrace, with a simple rectangular floor plan with no protruding rear returns or front porches, etc., thus limiting exposed heat loss surfaces. Despite this, a BER rating of G is a very poor result. There are a number of reasons for this:

• The small floor area -

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, which is 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 larger floor area will always have the better BER result than the smaller house.

• The high ventilation losses –

This house has very high ventilation rates for such a small floor area (including one chimney, two open flues, four permanent vents, and a kitchen and bathroom extract) thus ventilation heat losses are currently very high.

• Poor insulation levels and an inefficient boiler with a poor level of control

DEAP assessment 3 – featuring minor renovation

The third DEAP calculation includes all the lower-cost improvement measures as listed in the table describing Proposed Minor Renovation Project and Heritage Impact, including insulating the roof, replacing the single-glazed windows with high-performance triple-glazing, upgrading the existing front and rear solid doors, improving the draughtproofing (assuming a lower airtightness target of 2.5 m3/h/m2), replacing the existing boiler with a condensing combi boiler, upgrading the heating controls and installing low-energy lighting throughout.

These measures improved the BER and energy value to D2, 275.13 kWh/m2/yr, an improvement in the energy value of 45 % from DEAP assessment 2.

DEAP assessment 4 – featuring major renovation

For the fourth and final DEAP calculation, the major renovation project works were then applied, including installing external wall insulation to the front and rear façades, blocking the chimney stacks, upgrading the floor to achieve a U-value of 0.15 W/m2K and installing underfloor heating. Following these works, the complete external envelope has been upgraded. Also, to reflect the improvements to the building fabric, an airtightness level of 1.5m3/hr/m2 has been estimated.

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’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 1.19 W/Km2.

Upgrading the building fabric and installing an air to water heat pump brings the BER to an A3, 52.82 kWh/m2/y, improving the energy value by 89%.

Fuel Costs

Fuel costs as estimated by DEAP often vary 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 not 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.
• DEAP makes certain assumptions regarding the contribution of secondary heating systems, for example, if there is an open fire in the dwelling, DEAP assumes – subject to certain rules – that this contributes (typically 10%) to the overall heating of the dwelling.  The reality is that the fire place may never be used.

For these reasons, using DEAP to estimate fuel costs must be done with caution. The table above shows an estimated fuel cost of €1,791. This includes the cost of gas for heating and hot water, electricity for lights, pumps and fans and smokeless coal for the open fire. DEAP estimates the total cost of gas as €1,425 for space and water heating. The actual average annual cost of gas for this house is €540, just 38% of the DEAP calculated estimate. The reason for this difference is likely due to the fact that the house is actually heated for shorter periods and to lower temperatures. Following the complete fabric upgrade and the installation of an air-to-water heat pump, the DEAP estimated cost of electricity for space and water heating, lights and pumps and fans in the dwelling is just €310. In reality, the actual fuel bills and savings would depend on occupant use, a factor not accounted for in DEAP.