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 C3, 224.32 kWh/m2/yr. This result is 22% better than achieved by a typical pre 1940 mid-terrace house of similar size.

DEAP assessment 2 – featuring measured values

Following the initial BER Survey, an airtightness test was carried out, which gave an air permeability result of 10.64m3/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 Building Regulation airtightness requirement for new dwellings is 7m3/hr/m2.

The airtightness test identified the main leakage points as being in the kitchen behind the fixed seating arrangement and at the timber frame sash windows, which is a very common location for air leakage.

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 12.64m3/hr/m2 – worse (16%) than the actual tested air permeability rate.

In addition to measuring the airtightness level in the house, the measured U-values of 1.17 W/m2K and 1.62 W/m2K were applied to the main and return walls, respectively. These values are better than the DEAP default U-values of 1.64 W/m2K for 325mm solid brick and 2.1W/m2K for 225mm solid brick.

The second DEAP assessment includes the measured values for the wall U-values and air tightness, improving the BER slightly to C3, 203.79 kWh/m2/yr. This energy value was used as the baseline, from which the improvement effects of the proposed works were applied.

This is a large, three-storey mid-terraced dwelling with a four-storey return and kitchen extension. Consequently, the total heat loss element area of this house (exposed floors, walls, roof, windows etc.) is 151% of the floor area. This figure is lower than the average of 213% for pre-1945 dwellings. The advantage comes from the number of floors (three in main house and four in return) versus the limited exposed wall area (mid-terrace), thus limiting exposed heat loss surface per square metre.

Also, in a DEAP assessment, where the total energy consumption is divided by the dwelling floor area to calculate the BER, a larger floor area is advantageous.  In the DEAP calculation, while certain heat losses and gains are calculated based on the floor area, constant losses associated with the heating systems (and independent of floor area) are also accounted for. Therefore, in DEAP, if there are 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 a better BER result than the smaller house.

DEAP assessment 3 – featuring minor renovation #1

The third DEAP calculation includes all the improvement measures listed in the table describing Proposed renovation project #1 and heritage impact. These are the lower cost measures with minimal heritage impact including draughtproofing, blocking unused chimneys and installing a stove in the rear basement, insulating the timber frame extension and replacing its windows, insulating the roof of the bay window, insulating the attics, installing an efficient condensing gas boiler with improved heating controls and installing low energy lights throughout.

With these improvements the house achieves a C1 rating and an energy value of 164.85 kWh/m2/y - an improvement of just under 20% compared to DEAP assessment 2.

DEAP assessment 4 – featuring minor renovation #2

For the final DEAP calculation, the major renovation project works were then applied, as detailed in the table describing Proposed renovation project #2 and heritage impact. The works that improve the BER include insulating the basement floor, internally insulating the exposed walls at basement and first floor level, improving overall air tightness to achieve a target value of 1.5 m3/h/m2 and fitting secondary glazing to the existing sliding sash windows. The installation of demand-controlled mechanical extract ventilation typically has a negative impact on the BER score due to the slight increase in electricity demand from running the fan. However, the benefits from improved indoor air quality and moisture management will far outweigh any negative effect on the BER score.

Following these improvements, the BER was improved to B2, and the energy value was reduced to 111.56kWh/m2/yr, - a 45% reduction in energy value in comparison to DEAP assessment 2.

Fuel Costs

The energy costs estimated by DEAP often vary from the household’s 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. The reality is that 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 also 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 by 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 describing Key data of building energy assessment shows an estimated fuel cost of €3,220 for the building in its current condition. This includes the cost of gas for space heating of all the rooms in this big house, water heating, electricity for lighting, pumps and fans and smokeless fuel for the solid fuel stove.

Following the major renovation 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 €1,702. This figure represents a reduction in costs of 47%. In reality, not all the rooms would be heated 8 hours per day, which would significantly reduce these figures. The actual fuel bills and savings would really depend on occupant use, and this is not a factor accounted for in DEAP.