Dimensiones y características de los jóvenes

The Standard Assessment Procedure (SAP) is the main measure of Energy Efficiency Rating (EER) of domestic buildings in the UK. SAP considers heating, domestic hot water and lighting but not appliances, and is a rating of energy costs and carbon emission normalised by total floor area (Wright, 2008). The SAP EER values range from 1 to 100. Dwellings are also categorised into seven EER bands, from A to G. Table 2-4 illustrates the SAP EER of the domestic English housing stock for the year 2011. Large variation between EER of buildings can be seen. The reasons for this include the long period of time over which the buildings has been built, and the different building materials and techniques used, from stone and solid brick walls to the contemporary insulated cavity wall construction (Firth et al., 2010; Famuyibo et al., 2012).

Table 2-4. SAP Energy Efficiency Rating bands, values and the EER rating of the housing stock (DCLG, 2013).

EER of all dwellings EER

Bands SAP EER by band No. of dwellings in EER bands (000s) % of dwellings by EER band

Bands A/B (92-100)/(81-91) 38 0.2% Band C 69-90 3311 14.6% Band D 55-68 11199 49.2% Band E 39-54 6454 28.4% Band F 21-38 1363 6.0% Band G 1-20 389 1.7% Total 22754 100.0%

The average EER of the English housing stock in 2011 was 56.7 (DCLG, 2013). Only 14.8% of the housing stock had an EER rating of 69 or higher whilst 85.2% had less than 69 (Table 2-4). This is in sharp contrast to a typical Scandinavian house having

Thermal energy storage in residential buildings: A study of the benefits and impacts

an EER rating of 90-100 (Martiskanen, 2007), confirming the widely accepted notion that the UK housing stock is one of the least thermally efficient in Europe (DECC, 2012a; Martiskanen, 2007). The low EER is prevalent throughout all the dwelling types except the purpose built flats, approximately 55% of which have a rating of over 60.

One of the key determinants of thermal performance of dwellings is the level of heat loss. There are two ways by which heat loss occurs in buildings: 1) Ventilation heat loss and 2) heat loss through the building fabric. Ventilation heat loss (which can be deliberate for exchanging stale air with fresh air or uncontrolled infiltration caused by inadequate draught proofing etc.) occurs due to exchange of warm air from the inside with cold or ‘fresh’ air from the outside. Under steady state condition the heat loss from ventilation can be calculated using the equation:

Q = 0.33 N V Δt Equation 2-1

Where Q = rate of ventilation heat loss (W) V = Volume of room (m3₎

N = rate of air infiltration (number of air change per hour) Δt = Difference between the indoor and outdoor temperature

Building fabric heat loss is the result of the transfer of heat through the building fabric and depends on the thermal insulation present. The thermal transmittance (U-value) dictates the heat transfer rate through the building fabric (DCLG, 2013; Kane, 2013; Lowe et al., 1996). Heat transfer through the fabric is a function of the U-value, the area of the building envelope and the difference between the indoor and the outdoor temperatures, and so increasing the insulation level reduces the U-value and therefore the heat loss. Some of the main building fabric elements through which heat loss occurs are the external walls, external windows and doors, ground floor and the roof. (Famuyibo et al., 2012). Under steady state condition the building fabric heat loss can be calculated using the equation (Kane, 2013):

Q = U A Δt Equation 2-2

Where Q = rate of fabric heat loss (W) U = U-value (W/m2_K)

A = Area (m2₎

Δt = Difference between the indoor and outdoor temperature

At the whole house level the Heat Loss Coefficient (HLC) is used to describe the total heat loss from the building and is the sum of the fabric and ventilation losses. The Heat Loss Parameter (HLP) is the standardised measure of the building heat loss per

Thermal energy storage in residential buildings: A study of the benefits and impacts

unit floor area and can be useful for comparing the heat loss characteristics of different buildings (Kane, 2013).

HLC (W/K) = Ventilation heat loss (Pv) + Fabric heat loss (Pt) Equation 2-3

HLP = HLC_A Equation 2-4

Where A = total floor area (m2₎

Building regulation standards have been systematically upgraded over the last thirty years to influence improvement. The U-value of the key elements through which heat loss occurs was tightened as illustrated in Table 2-5. Whilst it has been possible to ensure compliance to these standards in new developments, through building control, the existing building stock is lagging behind. For example in 2011, whole house double glazing is only present in 76.3% of the existing dwellings in England whilst 11.9% had less than half or no double glazing at all. Also, 41.9% of the existing building stock had less than 200mm of loft insulation in comparison with the 2010 Building Regulation guideline being 250mm (HM Government (2010_PL1B)). Only 38.4% of the dwellings in England have cavity wall insulation out of the possible 69% with cavity wall construction (DCLG, 2013). These suggest that a significant number of the existing buildings are lagging behind the latest building regulation and just barely conforming to the 1990s edition.

Table 2-5. U-value of the main building fabrics and the air infiltration level by building regulation standards (HM Government, 2010_PL1A; HM Government, 2010_PL1B). Floor W/m2_.K Infiltration ACH Ext. Wall W/m2_.K

Windows & Doors W/m2_.K Loft/Roof W/m2_.K 1981 Regulation 0.74 2.00 0.60 5.70 0.40 1990 Regulation 0.45 1.75 0.45 3.30 0.25 2002 Regulation 0.25 0.75 0.35 2.00 0.16 2010 Regulation 0.17 0.40 0.22 0.96 0.14