Energy

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 DEAP default values for existing dwellings. The default U-values, estimating heat loss through the building fabric, are based on the general build-up of the building envelope elements and the age of construction. Default U-values are applied where there is simply not enough information on the building fabric to carry out more accurate U-value calculations. Using the appropriate default values, the calculated BER and energy value of this house was D1, 227.21 kWh/m2/yr.

DEAP assessment 2 – featuring measured values

Following the initial BER Survey, an air tightness test was carried out, which gave an air permeability result of 10.29m3/hr/m2 at a 50 Pascal pressure differential. The air tightness test measures air leakage through gaps and cracks in the building fabric. This uncontrolled air infiltration results in heat loss and increased space heat demand.

A default value for airtightness can be applied where an airtightness test has not been carried out. This DEAP default value for air tightness is estimated based on the type of ground floor, the main structure of the dwelling, the percentage of openings which are draughtproofed and the number of storeys in the dwelling. From the information collected during the survey, the DEAP default value for airtightness was 12.40m3/hr/m2 – worse (17%) than the actual tested air permeability rate.

In addition, a measured U-value of 1.17 W/m2K was applied to the 325mm solid brick walls, see section on Solid Walls [link to follow], for more on measured U-values. This measured U-value is 29% better than the DEAP default U-value for 325mm solid brick which is 1.64W/m2K.

Inputting these calculated values for the wall U-value and air tightness improves the BER and energy value to a C3, 211.68 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.

DEAP assessment 3 – featuring minor renovation #1

The third DEAP calculation includes the improvement measures (lower cost measures with minimal heritage value) listed in the table describing Proposed Renovation Project #1 and Heritage Impact.  Of these, the measures impacting on the BER include draughtproofing, fitting dampers to chimneys to reduce ventilation heat loss, replacing the two intermittent extract vents with a whole-house extract ventilation, insulating both attics, improving the heating system controls to provide independent time and temperature control of more than one space heating zone and installing low-energy lights throughout.

Following these improvements, the BER was improved to C1 and energy value was reduced to 170.02 kWh/m2/yr, an improvement of almost 20% compared to DEAP assessment 2.

DEAP assessment 4 – featuring minor renovation #2

For the fourth and final DEAP calculation, the works listed listed in the table describing Proposed Renovation Project #2 and Heritage Impact were then applied, including re-insulating the pitched ceiling in the bathroom (to achieve a new U-value of 0.24 W/m2K) , internally insulating the exposed walls, improving overall air tightness to achieve a target value of 3.0 m3/h/m2, insulating the panels of the front door, fitting secondary glazing to the existing sliding sash windows and installing an air to water heat pump.

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 (note that the names of schemes change over time), SEAI had 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 (and thus space heat demand) is sufficiently low for the heat pump to operate efficiently. The improvement works to this house have reduced the heat loss indicator (HLI) from 3.11 W/Km2 to 1.86 W/Km2. Upgrading the building fabric and installing an air-to-water heat pump improves the BER to an B1, 80.69 kWh/m2/y, improving the energy value by 62%.

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 key data of the building energy assessment provided in the table shows an estimated fuel cost of €2,368 for the building in its current condition. This includes the cost of gas for space and water heating, smokeless solid fuel and 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 €1,195. This figure represents a saving of approximately 50%. In reality, the actual fuel bills and savings would depend on occupant use, a factor not accounted for in DEAP.