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. The dwelling achieves a D2 rating.

This result reflects the existing fabric upgrades and the boiler and heating control upgrade that have been carried out by the current owners of the house.

DEAP assessment 2 – featuring measured values

The first DEAP assessment was then amended to account for the airtightness test result of 13.62 m3/h/m2 and the measured U-values of 1.19 W/m2K for the ground-floor storey walls and 1.62 W/m2K for the first-floor walls. These measured U-values are considerably better than the default U-values of 1.64 W/m2K for 325mm solid brick walls and 2.1 W/m2K for 225mm solid brick walls. As discussed earlier, the airtightness result is very poor due to the leakiness of the single-glazed metal framed windows and at the base of the front door. This measured value for airtightness, while poor when compared to the other case study houses, is still better than the default value for airtightness which is applied when an airtightness test has not been carried out. This default value is based on the number of storeys, the type of structure, the type of ground floor and the % of openings that are draughtproofed. Applying these measured values have improved the rating by just over 6% to D2, 265.57 kWh/m2/y.

The heat loss indicator – the total heat loss (W/K) per square metre of dwelling, which takes account of ventilation and fabric heat loss is 3.63 W/m2K.

DEAP assessment 3 – featuring minor renovation

A third DEAP calculation was carried out incorporating all the minor renovations listed 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 C3, 220.13 kWh/m2/y – an improvement of just over 17%. The main aim of this upgrade is to reduce air infiltration and reduce the heat loss through the pitched ceilings and in the short stud walls of the attic conversion. The airtightness target for this minor renovation is set at 6.0m3/h/m2. The installation of secondary glazing to all single-glazed metal windows significantly reduces air infiltration and would help to achieve this target. The upgrade of the pitched ceilings, including insulation to achieve a U-value of 0.36 W/m2K and an air and vapour control layer will also reduce air infiltration. Improved ventilation will be provided with demand controlled mechanical extract ventilation. As the boiler and heating controls were recently upgraded, the only heating system upgrade proposed for this minor renovation is to replace the old hot water cylinder with a factory insulated cylinder and insulation to all pipework.

The works providing the biggest impact on the BER score is the 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 fourth and final DEAP calculation takes account of the impact of the major renovations detailed in the table describing Proposed Major Renovation Project and Heritage Impact. This major renovation includes internal wall insulation to all un-insulated original walls to achieve a U-value of 0.35 W/m2K and upgrading the external wall insulation to the rear extension and insulating the wall between the garage and the kitchen, resulting in an upgrade to all of the dwellings heat loss walls. The upgrade to the heat loss ceilings is also completed here with an upgrade to the flat roof over the kitchen extension to achieve a U-value of 0.15 W/m2K.  It is also proposed to reduce ventilation heat loss results by blocking up permanently blocking two chimneys and three open flues, leaving one open flue for the existing solid fuel stove in the living room Also, to reflect the improvements to the building fabric, an air tightness target of 2.5m3/hr/m2 has been set.

These improvements reduce the total ventilation and fabric heat loss to 1.83 W/Km2. 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 Better Energy Homes 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 3.63 W/Km2 to 1.83 W/Km2 – reducing the heat loss by 50%, thereby 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, 70.85 kWh/m2/y, improving the energy value by 73%.

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. This often overestimates the use of room heaters.

For these reasons, estimating fuel costs, using DEAP, must be done with caution. The table above shows an estimated fuel cost of €2,869 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 stove.

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 €1,072. This figure represents a saving of 63%. In reality, the actual fuel bills and savings would depend on occupant use, a factor not accounted for in DEAP.