Section 6 Elemental and Heat Loss Methods (including building services requirements)

  

 

 

"To comply with this method the building envelope must provide minimum levels of thermal insulation as set out in J8.3 and areas of windows, doors and rooflights as set out in J8.4." (Part J, paragraph J8.2).

 

"The individual specified building elements must have U-values in accordance with the table to this standard." (paragraph J8.3).

 

For each heated room, all heat-loss elements are subjected to the U-value checks set out in paragraph J8.3.

 

The Table 8.3 category ‘Pitched roof with insulation between rafters’ is applied to ceiling elements linking to rooms of type ‘Unheated space with pitched roof and insulation between rafters’.

 

The Table 8.3 category ‘Pitched roof with insulation between joists is applied to ceiling elements linking to rooms of type ‘Unheated space with pitched roof and insulation between joists.

 

Ceilings linking to other types of unheated space, and roof elements, are treated as ‘Flat roof or roof with integral insulation’.

 

In the case of windows, roof windows and personnel doors the check is applied to an area-weighted average U-value for the whole building. The U-value requirement in Table 8.3 depends on the type of frame (metal or wood/PVC). In cases where there is a mixture of frame types the required U-value is set to the value appropriate to the type of frame accounting for the greater overall area, as stipulated in a reply posted on the Part L FAQ website^[3].

 

Display glazing, as specified by the check-box in APcdb, is not excluded from the Table 8.3 checks (contrary to the treatment in Part L (England & Wales)).

 

Vehicle access and similar large doors, as specified by the check-box in APcdb, form a special category in Table 8.3 with U-value limit 0.7 W/m²K.

 

Elements defined as walls in ModelIT are treated as roofs if they have a slope less than 70 degrees, and elements defined as roofs in ModelIT are treated as walls if they have a slope greater than or equal to 70 degrees. The same principle applies to windows and rooflights.

 

For link-exposed elements, Table 8.3 note 1 offers two options. The software always applies EN ISO 13798:1999 (the less stringent requirement).

 

"The specified building elements must have areas of windows, doors and rooflights not more than those prescribed in the table to this standard" (Part J, paragraph J8.4).

 

In accordance with paragraph 8.4, checks are performed on the total areas of heat-loss windows, doors and rooflights in heated rooms. A heat-loss element is any environment-exposed, link-exposed or earth-contact element.

 

The percentage figure for windows and doors is calculated as the total area of heat-loss windows (excluding display windows) and doors (excluding vehicle access and similar large doors and any doors used to represent wall or roof elements) divided by the overall wall area above ground level, which is calculated as the sum of the areas of all heat-loss walls, windows and doors excluding earth-contact walls but including all types of window and door. Earth-contact walls are excluded from the area calculation in accordance with a ruling posted on the Part L FAQ website3. Earth-contact walls are identified as walls with adjacency type ‘Outside air with offset temp.’ or ‘Temp. from profile’. Any windows and doors with these adjacency types are also classified as earth-contact walls.

 

The percentage figure for rooflights is calculated as the total area of rooflights (including any link-exposed ceiling windows) divided by the overall roof area, which is calculated as the total area of roofs and rooflights excluding earth-contact ceilings but including any link-exposed ceiling windows and display rooflights. Earth-contact ceilings are identified as ceilings with adjacency type ‘Outside air with offset temp.’ or ‘Temp. from profile’. Any rooflights with these adjacency types are also classified as earth-contact ceilings.

 

Any rooflight assigned a ‘display window’ glazing type is treated as an ordinary rooflight.

 

Buildings of type ‘Hospital’ are placed in the category ‘Residential buildings (where people temporarily or permanently reside)’ – that is, buildings in Purpose Group 2.

 

Buildings of type ‘School’ are placed in the category ‘Places of assembly, offices and shops’ – that is, buildings in Purpose Groups 4 & 5.

 

"When using this method - a. the total rate of heat loss through the envelope of the proposed building must not be more than that from a notional building of the same size and shape designed to comply with the Elemental Method...." (Part J, paragraph J8.5).

 

"When comparing the proposed building with the notional building –

 

a. if the U-value of the floor next to the ground in the proposed building is less than that required by J8.3, with no added insulation, then the lower value must be used in the notional building: and

...

c. a maximum of half of the permitted rooflight area can be converted into an increased area of window and doors." (Part J, paragraph J8.6).

 

Clause 8.5c causes some difficulty. The equivalent clause in Part L (England and Wales) is clarified by an example in ADL2 Appendix E, which makes clear that (at least in Part L) this requirement is more stringent than a literal reading might suggest, and is to be interpreted as

 

“c) no more than half of the allowable rooflight area can be converted into an increased area of window and doors or traded off in any other way (for instance against glazing U-values)”.

 

It is thus equivalent to the following constraint on the notional building:

 

"The area of rooflights in the notional building should not exceed that in the proposed building by more than half the Table 8.4 allowance (that is, by more than 10%)".

 

This is the interpretation applied in the software for both Part L & Section 6. However, it is inconsistent with the example given in Part J Appendix H, which appears to ignore clause J8.5c.

 

The constraints on floor U-value and glazing/door area are applied by the software when setting the properties of the notional building, and their effect can be seen in the tables presented in the results file. Display windows are subject to the same U-value constraints as other windows and doors. Paragraph 8.6b is dealt with as a separate requirement (see below).

 

The area of vehicle access and similar large doors in the notional building is set equal to the area of such doors in the proposed building, since Table J8.4 imposes no area limit in this case. The same principle applies to display glazing. In accordance with Table J8.3, the U-value for vehicle access doors is set to 0.7 W/m2/K in the notional building.

 

The apportioning of area between personnel doors and windows in the notional building makes no difference to the heat loss characteristics. However, the rule applied is that the area of personnel doors in the notional building is normally set equal to the area of such doors in the proposed building, any adjustments being made to window area. The only exception to this rule would be in the unlikely event that personnel doors alone accounted for more than the Table J8.4 allowance.

 

The comparison between the proposed building and the notional building appears in the results file as a table showing areas, average U-values and heat loss coefficients for each category of heat-loss element. Average U-values for the proposed building (Uact) and for the notional building (Uref) may be read off from the bottom of the table.

 

A separate table displays, for the proposed and notional buildings, the window/door area percentage for the walls and the rooflight area percentage for the roofs.

 

Finally, Ureq is compared with the average U-value for the proposed building (Uact).

 

"When using this method... b. the U-value of any building element must not be more than that shown in the table to this standard." (Part J, paragraph J8.5).

 

These checks follow the same pattern as those described in section E 1.1.1 U-value (Table J8.3) Requirement, but apply only to roofs, walls and floors.

 

 

"When comparing the proposed building with the notional building –

 

b. if the total area of windows, doors and rooflights in the proposed building is less than the total area required by J8.4, then the average U-value of the roof, wall or floor cannot exceed the appropriate value given in the Table to J8.3 by more than 0.02 W/m2K." (Part J, paragraph J8.6).

 

A calculation is carried out to determine the maximum allowable area of heat-loss openings (windows, personnel doors and rooflights) permitted by the Table J8.4 requirements. If the actual area of heat-loss openings is less than this figure, the average U-values of the roofs and heat-loss walls and floors are checked against the appropriate Table J8.3 values plus 0.02 W/m2K.

 

In the table displaying element categories failing this test, the category ‘Flat roof or roof with integral insulation’ includes any earth-contact ceilings, and the category ‘Wall’ includes any earth-contact walls.

 

 

"The building's fabric must be constructed to minimise thermal bridges and gaps in the insulation layer(s)..." (Part J, paragraph J9.1).

 

"The infiltration of air into a building through extraneous air paths must be limited as far as is reasonably practical."  (Part J, paragraph J10.1).

 

These requirements cannot be analysed in software, but reference is made to them in the results file for reasons of completeness.

 

 

"The heating system of a building must be designed and installed to make efficient use of energy for the conservation of fuel and power." (Part J, paragraph J11.1) 

 

"The requirements of J11.1, as regards the efficiency of the boiler or other primary heat source, will be met - a. where the rating-weighted average carbon intensity of the boiler or other primary heat source is in accordance with Table 1 to this standard; or b. in the case of a liquid or gaseous fuelled boiler only, by compliance with the Boiler Efficiency Regulations 1993 and 1994" (Part J, paragraph (J11.1)) (Option b is not covered by the software.)

 

The Heating Systems analysis performed by the software is based solely on the data entered via the Heating Systems tab of Building Regs Building & System data. Results are presented both in the interface and in the Part J results file.

 

The interface provides facilities for specifying one or more heating systems and describing their characteristics. It also displays the Part J analysis results for the currently defined set of systems.

 

Equation 1 to (J11.1) provides the basis for the analysis:

 

A = B / C

 

where:

 

A          is the carbon intensity of the heating system (kgC/kWh of useful heat)

B          is the carbon emission factor of the fuel (kgC/kWh of delivered fuel) (see Table 2 to (J11.1))

C          is the gross thermal efficiency of the heating system (kWh of heat divided by kWh of delivered fuel)

 

In the case of heating provided by combined heat and power, equation (2) to (J11.1) applies:

 

A = (B / D) – (F / E)

 

where:

 

A          is the carbon intensity of the heating system (kgC/kWh of useful heat)

B          is the carbon emission factor of the fuel (kgC/kWh of delivered fuel) (see Table 2 to (J11.1))

D          is the heat output ratio of the CHP engine (kWh of heat per kWh of delivered fuel)

E          is the electrical output ratio of the engine (kWh of electricity per kWh of delivered fuel)

F          = 0.123 kgC/kWh is the carbon emission factor for grid supplied electricity

 

The software extends the treatment (in line with Part L) to cover cases where there is more than one heating system. In such cases the expression for the mean carbon intensity of the heating systems becomes a weighted sum over all the heating systems in the building:

 

A_mean = (1/ΣP) Σ(P A)

 

where:

 

A          is the mean carbon intensity of the heating systems (kgC/kWh of useful heat)

P          is the percentage of total building heating at either 30% or 100% design capacity

A          is the carbon intensity of each contributing heating system (kgC/kWh of useful heat)

 

These equations are used to calculate carbon intensity values for the heat generating equipment working at a) the design capacity of the heating system and b) 30% of the design capacity.

 

The carbon intensity values are then compared with entries in Table 1 to (J11.1) to generate:

 

a)     a pass/fail result based on the performance at design capacity.

b)     a pass/fail result based on the performance at 30% of design capacity.

c)     an overall pass/fail result.

 

Table 1 to (J11.1) gives maximum allowable carbon intensities at design capacity and 30% of design capacity for: 1. Natural gas, 2. Other fuels. In cases where more than one heating fuel is used, an average of the values in Table 5 is used, weighted by system output at design capacity or 30% design capacity as appropriate.

 

The requirements on heating controls are set out in paragraphs J11.2-J11.5. These requirements cannot be analysed in software but are included for completeness.

 

The requirements on the insulation of pipes, ducts and vessels are set out in paragraphs J11.6-J11.7. These requirements cannot be analysed in software but are included for completeness.

 

"A building provided with artificial lighting must have general purpose artificial lighting systems designed to make efficient use of power, except - a. emergency lighting; and b. specialist process lighting; and c. buildings with a floor area not more than 100m²." (paragraph J12.1).

 

Lighting system requirements are not analysed by the current Part J software implementation.

 

 

"A building incorporating air conditioning or mechanical ventilation must be designed and constructed so that - a. the form and fabric of the building do not result in a requirement for excessive installed capacity of cooling equipment; and b. fans, pumps, refrigeration equipment and other components are reasonably efficient and appropriately sized to have no more capacity for demand and standby than is necessary; and c. there are appropriate means of managing, controlling and monitoring the operation of equipment and systems." (paragraph J13.1).

 

"The requirements of J13.1, for energy efficiency of air conditioning and mechanical ventilation will be met - a. for buildings of purpose group 3, by achieving a Carbon Performance Index of at least 100, or in the case of a conversion, at least 90....' (Part J, paragraph (J13.1))

 

The CPI Method applies only to offices (buildings in Purpose Group 3). For the method to be applied the building type must be set to ‘Office’ and the check-box ‘Include Office CPI Method’ must be ticked.

 

The data required by the Office CPI Method is entered via the tabs ‘Office CPI Mech Vent’ and ‘Office CPI Air Cond’ in the Part J Building & System Data dialogue. If both mechanical ventilation and air conditioning are used in the building, compliance must be demonstrated for both systems. Results from the analysis are displayed in boxes at the bottom of the data input tabs and are updated as the input data is edited.

 

The calculation of a CPI value involves first calculating a ‘Carbon Performance Rating’ (CPR) as a sum of contributions of the form:

 

CPR = P x H x C x F

 

where:

 

P = Input power rating of the plant (kW/m² for the calculation, but W/m² for data entry)

H = Number of hours per year that the plant operates (standard values assumed)

C = Conversion factor for the fuel used (kgC/kWh)

F = Factor depending on provisions made to control and manage the installed plant

 

Parameter P forms part of the input data. Part J Appendix K provides detailed procedures for setting parameters H, C and F.

 

The CPI rating is calculated as a constant divided by the Carbon Performance Rating. To pass the Part J checks the CPI rating must exceed a given value.

 

 

The method is set out in Part J paragraphs (J13.1) and Appendix K, from which the following extracts are taken:

 

"The assessment is based on the calculation of a Carbon Performance Index using the following relationship:

 

CPI(MV) = MV / (PD x HD x CD x FD)

 

where the value of the factor MV=800 has been set so that the design is considered to represent acceptable practice where the result of the calculation is 100 or greater" (paragraph K2.1) "... or in the case of a conversion, at least 90' (paragraph (J13.1))

 

The suffix D refers to plant for air distribution.

 

 

The method is set out in ADL2 paragraphs (J13.1) and Appendix K, from which the following extracts are taken:

 

"The assessment is based on the calculation of a Carbon Performance Index using the following relationship:

 

CPI(ACMV) = ACMV / (PD x HD x CD x FD + PR x HR x CR x FR)

 

The value of the factor ACMV=1200 has been set so that the design is considered to represent acceptable practice where the result of the calculation is 100 or greater" (Part J, paragraph K2.2) "... or in the case of a conversion, at least 90' (Part J, paragraph (J13.1))

 

The suffixes D and R refer to plant for air distribution and refrigeration, respectively.

 

“The requirements of J13.1, for energy efficiency of air conditioning and mechanical ventilation, will be met - … b. for buildings of purpose groups 2 and 4 to 7, by providing air conditioning or mechanical ventilation with a total specific fan power (i.e. the design power of all fans in the distribution system divided by the design ventilation rate through the building) not greater than 1.5 W/ls^-1.

 

These requirements are not analysed by the software.