Domestic and non-domestic energy performance certificates review: supplementary notes

5. Community Heating

Community heating is defined in RdSAP under Convention 4.05:

"A system in which a heat generator provides heat and/or hot water to more than one premises."^[22]

The convention then notes that "each dwelling to be assessed individually."

5.1 Community Heating in RdSAP

In RdSAP, community heating is entered into the program via four considerations:

• the heat source: boilers / CHP / heat pump
• the system fuel: mains gas / LPG / oil / mineral oil or biodiesel / biodiesel from any vegetable source / biodiesel from vegetable oil only / B30D / coal / biomass / electricity / waste combustion / biogas / waste heat / geothermal heat source
• the main heating controls: none / programmer only / room thermostat only / TRVs only / programmer and room thermostat / programmer and TRVs / two or more room thermostats
• the method of charging for consumption: whether flat rate charging or consumption-based charging

All other variables used in the RdSAP calculation are defaulted to in the program, for example, the system efficiency, the characteristics of the distribution network, and the price of the system fuel, regardless of the actual age of the system, the system's efficiency, its distribution system, or the actual fuel used. It also appears that RdSAP uses a single default value for most of these variables.

Table DH1 presents the results of an RdSAP assessment for a single, multi-storey flat heated by a community heating boiler system^[23] where only the main fuel was changed in each iteration. What is evident from Table DH1 is that regardless of the main heating fuel selected, the results are identical for the SAP score and various calculated fuel costs. The Environmental Impact (EI) rating and the CO₂ emissions change depending on the fuel, but nothing else.

Table DH1: Results of an RdSAP Assessment of Flat heated by Community Heating

	Community Heating Boiler Fuel
	Mains gas	LPG	Coal	Biomass
SAP rating	73	73	73	73
EI rating	62	58	37	98
CO2 tonnes/year	6.3	7.1	11	0.6
Lighting £/year	£134	£134	£134	£134
Space heating £/year	£1190	£1190	£1190	£1190
Water heating £/year	£128	£128	£128	£128

When the RdSAP assessment was repeated for the same multi-storey flat but assuming a combined heat and power (CHP) system^[24] instead of community heating boiler system^[25], and the changing of the main system fuel repeated, the SAP score improved, and the space and water heating fuel costs reduced, but they remained constant across all four system fuels. Again, the EI rating and the CO₂ emissions changed depending on the system fuel (see Table DH2).

Table DH2: Results of an RdSAP Assessment of Flat heated by Combined Heat and Power scheme

	Combined Heat and Power System Fuel
	Mains gas	LPG	Coal	Biomass
SAP rating	76	76	76	76
EI rating	68	62	37	111
CO2 tonnes/year	5.5	6.4	12.0	-1.6
Lighting £/year	£134	£134	£134	£134
Space heating £/year	£1074	£1074	£1074	£1074
Water heating £/year	£115	£115	£115	£115

The problem here is that if you were to upgrade an existing community heating or CHP scheme with a newer more efficient boiler plant, or a better insulated distribution system, you would get exactly the same SAP and EI rating and CO₂ and fuel cost results as before, as long as the system fuel did not change. There would be no improvement in any of the energy performance indicators - not exactly an incentive for investing in a system upgrade. If you changed the system fuel (for example, switched from mains gas to biomass) then the rating and fuel costs would remain the same although the CO₂ emissions would change.

5.2 Community Heating in Full SAP

A full SAP assessment requires more information on a community heating / CHP system to complete an assessment on a dwelling:

• the source of data: SAP Table / manufacturer declared
• the type of System: CHP / boilers / heat pump / geothermal heat source / waste heat from power station
• the system fuel: mains gas / LPG / oil / mineral oil or biodiesel / biodiesel from any vegetable source / biodiesel from vegetable oil only / B30D / coal / biomass / waste combustion / biogas
• the fraction of heat: the fraction of dwelling heat coming from the community heating system
• the efficiency of the system: the efficiency of the community heating system (if from manufacturer declared or system records, it can be whatever values is declared; if from the SAP table: community heating and CHP are deemed to be 75% efficient, geothermal heat source and waste heat from power station are deemed to be 100% efficient, and a heat pump is deemed to be 300% efficient)
• the Heat to Power ratio: the efficiency of the thermal generation divided by the efficiency of the electricity generation
• the Distribution Loss Factor: the distribution Loss Factor can be calculated using equations in the SAP manual or selected in certain instances from Table 12c of the SAP 2012 manual – see over the page for both approaches taken from the SAP 2012 manual.
• the main heating controls: none / programmer only / room thermostat only / TRVs only / programmer and Room thermostat / programmer and TRVs / two or more room thermostats
• the method of charging for consumption: whether flat rate charging or consumption-based charging
• the heat emitter in the dwelling: radiators, underfloor (timber) / underfloor (concrete) / underfloor (timber) and radiators / underfloor (concrete) and radiators / underfloor (screed) / underfloor (screed) and radiators / warm air by fan coil

A full SAP assessment needs all of the data of RdSAP and much more, with consequential implications for the calculated SAP score and space and water heating costs. However, even within the SAP process, the system fuel does not affect the fuel cost calculations (see Table DH3), but does affect the EI rating and CO₂ emission results. If the efficiency of the boiler, the fraction of heat, the heat to power ratio, Distribution Loss Factor, and controls remain the same changing the system fuel will have no effect on the SAP-calculated rating. However, in a full SAP assessment the efficiency of the boiler plant and the heat to power ratio are unlikely to remain the same for different community heating or CHP schemes, so the actual results will vary in practice.

Table DH3: Results of a full SAP Assessment^[26] of Flat heated by Combined Heat and Power scheme

	Combined Heat and Power System Fuel
	Mains gas	LPG	Coal	Biomass
SAP rating	80	80	80	80
EI rating	89	85	63	98
CO2 tonnes/year	0.709	0.978	2.475	0.134
Lighting £/year	£37	£37	£37	£37
Space heating £/year	£208	£208	£208	£208
Water heating £/year	£60	£60	£60	£60

In Table DH4, the difference between the full SAP and RdSAP results for the same multi-storey flat are compared directly. As can be seen, RdSAP results in a lower SAP score being calculated, a lower EI rating, higher CO₂ emissions, and higher space and water heating costs.

Table DH4: Comparative Results of a full SAP Assessment and RdSAP assessment of the of same multi-storey flat being heated with a Combined Heat and Power scheme

	Combined Heat and Power System Fuel
	Mains gas	LPG	Coal	Biomass	RdSAP[27]
SAP rating	80	80	80	80	76
EI rating	89	85	63	98	78
CO2 tonnes/year	0.709	0.978	2.475	0.134	1.60
Lighting £/year	£37	£37	£37	£37	£48
Space heating £/year	£208	£208	£208	£208	£263
Water heating £/year	£60	£60	£60	£60	£92

5.3 Distribution Loss Factor

A significant factor in determining the overall efficiency of a community heating / CHP system is the distribution loss factor, that is, how much heat is wasted in getting the heat from the boiler plant to the heat emitters. This is an area of the SAP methodology that appears to be well-outdated. The default distribution loss factors, as can be seen in Figure DH1, differentiate between systems installed either before or after 1991. Have there been no improvements in distribution systems in the almost 30 years since?

However, in RdSAP, as there is no allowance to select the Distribution Loss Factor for a community heating / CHP system, it is defaulted to the value for a pre-1990 pre-insulated system, that is, a factor of 1.10^[28]

Figure DH1: Default Distribution loss factors – Table 12c, SAP 2012 methodology^[29]

The use of these default values are specifically limited to situations where any of the following conditions are met:

1) The only dwellings connected to any part of the network are flats, or

2) The total trench length of the network is no longer than 100 metres, or

3) The linear heat density is not less than 2 MWh/year per metre of network^[30].

Where these SAP Table 12c values cannot be used , the calculation of the Distribution Loss Factor is set out section C3.1 of the SAP methodology (see Figure DH2 below).

Figure DH2: Calculating the Distribution loss factor – Section C3.1, SAP 2012 methodology^[31]

Regardless of how the Distribution Loss Factor is derived in a full SAP assessment, there is no opportunity to change it all in RdSAP.

5.4 An Aberdeen Case Study

Differences in the results calculated by full SAP and RdSAP can be magnified because community heating and CHP systems usually impact on significantly more than 2 dwellings.

For a specific 55-flat, multi-storey dwelling block in Aberdeen being considered at the time of these assessments for connection to a CHP system, all of the different flat types were surveyed, and full SAP assessments completed to assess the potential CO₂ emissions associated with switching from electric storage heating to CHP. These assessments have been reworked in a current full SAP program^[32] and the sample results set out in Table DH5.

Table DH5 – Sample audits for multi-story block in Aberdeen: Full SAP analysis

Flat	position	CHP - full SAP analysis – pre-install EPC data
		Full SAP SAP score	Full SAP Space heating _hot water + lighting costs (£/year)	Full SAP CO2tonnes / year	Full SAP EI score	Full SAP Space Heating demand kWh/year
1 meadow	GF	75	563	1.58	83	8749
5 meadow	FF	79	350	0.868	88	3928
6 meadow	FF	79	348	0.86	88	3862
7 meadow	FF	76	402	1.059	85	5411
8 meadow	FF	76	401	1.042	86	5287
9 meadow	FF	76	394	1.017	86	5096
10 meadow	FF	76	402	1.059	85	5411
11 meadow	MF	80	324	0.779	89	3227
42 meadow	MF	82	276	0.619	91	1968
28 meadow	MF	80	328	0.793	89	3356
56 meadow	TF	77	384	0.985	87	4809
57 meadow	TF	79	339	0.83	89	3629
55 meadow	TF	77	385	1.001	86	4954

The same dwellings were also assessed using an approved RdSAP v9.93^[33]. These results are set in Table DH6.

Table DH6 – Sample audits for multi-story block in Aberdeen: RdSAP analysis

Flat	position	CHP RdSAP analysis – pre-install EPC data
		RdSAP SAP score	RdSAP Space heating _hot water + lighting costs (£/year)	RdSAP CO2 tonnes / year	RdSAP EI score	RdSAP Space Heating demand kWh/year
1 meadow	GF	70	682	3.1	67	8336
5 meadow	FF	75	411	1.7	77	3656
6 meadow	FF	78	364	1.4	81	2712
7 meadow	FF	71	493	2.1	71	5363
8 meadow	FF	72	482	2.1	72	5072
9 meadow	FF	74	438	1.8	75	4171
10 meadow	FF	71	493	2.1	71	5363
11 meadow	MF	77	375	1.5	80	2954
42 meadow	MF	80	328	1.2	84	1990
28 meadow	MF	76	393	1.6	79	3278
56 meadow	TF	73	461	1.9	73	4650
57 meadow	TF	75	416	1.7	77	3736
55 meadow	TF	72	472	2	72	4949

The differences between the full SAP and RdSAP assessment for these same flats are set out in Table DH7. The SAP scores vary between 1 SAP and 5 SAP points less in the RDSAP assessment than in full SAP assessment; the EI scores vary by between 7 and 16 rating points less in the RdSAP assessment; the CO₂ emissions vary by between 0.54 and 1.52 tonnes more per year in the RdSAP analysis; and the fuel costs vary by between £16 and £119 more per year in the RdSAP analysis.

Table DH7: Summary of differences between full SAP assessment in Table DH5 and RdSAP assessment in Table DH6

Flat	position	SAP score difference	Fuel Cost difference (£/year)	CO2 emissions difference (tonnes of CO2/year)	EI difference	Space heating demand difference (kWh/year)
1 meadow	GF	-5	119	1.52	-16	-413
5 meadow	FF	-4	61	0.832	-11	-272
6 meadow	FF	-1	16	0.54	-7	-1150
7 meadow	FF	-5	91	1.041	-14	-48
8 meadow	FF	-4	81	1.058	-14	-215
9 meadow	FF	-2	44	0.783	-11	-925
10 meadow	FF	-5	91	1.041	-14	-48
11 meadow	MF	-3	51	0.721	-9	-273
42 meadow	MF	-2	52	0.581	-7	22
28 meadow	MF	-4	65	0.807	-10	-78
56 meadow	TF	-4	77	0.915	-14	-159
57 meadow	TF	-4	77	0.87	-12	107
55 meadow	TF	-5	87	0.999	-14	-5

Some of these individual assessments were representative of other dwellings within the same block. The multipliers are provided in Table DH 8, along with the aggregated total differences in CO₂ emissions, space heating consumption, and fuel costs for the different flat types respectively.

Table DH8: Aggregated differences between full SAP assessment in Table DH5 and RdSAP assessment in Table DH6 for CO₂ emissions, fuel costs and space heating energy consumption

Flat	position	Multiplier	Total CO2 emissions difference (tonnes of CO2/year)	Total Fuel Cost difference (£/year)	Total Space heating demand difference (kWh/year)
1 meadow	GF	1	1.52	119	-413
5 meadow	FF	1	0.832	61	-272
6 meadow	FF	1	0.54	16	-1150
7 meadow	FF	1	1.041	91	-48
8 meadow	FF	1	1.058	81	-215
9 meadow	FF	1	0.783	44	-925
10 meadow	FF	1	1.041	91	-48
11 meadow	MF	14	10.094	714	-3822
42 meadow	MF	14	8.134	728	308
28 meadow	MF	14	11.298	910	-1092
56 meadow	TF	2	1.83	154	-318
57 meadow	TF	2	1.74	154	214
55 meadow	TF	2	1.998	174	-10
Total			41.909	£3337	-7791

When aggregated across the whole of the 55 flats within this multi-storey block, when compared to the full SAP assessment, RdSAP over-estimates the CO₂ emissions by 41.909 tonnes per year; it over estimates the fuel bill by £3,337 per year; and it over estimates space heating consumption by 7791 kWh per year.

5.5 Community Heating and CHP Data Availability

The differences between the results in a full SAP and an RdSAP assessment for community heating and CHP have important implications in the assessing of local heat networks. Would it be possible to complete a full SAP analysis on each dwelling connected to a community heating or CHP scheme? The likelihood is not, as the detailed information required on the operational parameters of the community heating or CHP scheme are not necessarily readily available. Further you would currently need to use a full SAP program to complete the assessment. Under current arrangements of lodging EPCs, it is possible for a full SAP assessment to be lodged in the Scottish Register for an existing dwelling. However, to do so you may need to be both a qualified RdSAP assessor and a qualified assessor for new build (what is called an on-construction dwelling energy assessor).

A way around the need to use a full SAP program would be to allow extended data entry for community heating and CHP schemes within RdSAP. The precedent exists in that there are several areas where an assessor can 'turn on' extended data entry with RdSAP (for example, with rooms in the roof and windows). However, allowing extended data entry does not provide all of the necessary data to complete the SAP assessment.

The PCDF has introduced extended data into the information that assessors can select from the PCDF in a full SAP and RdSAP assessments. The extended boiler database is a good example of this and very useful. A recent development was to include information on community heating schemes. To date, however, there is only one such scheme in the PCDF that may be selected – the Lerwick community heating scheme (see Figure DH3 below). More community and CHP schemes need to be encouraged to supply their data to the PCDF.

Figure DH3: PCDF data for Lerwick District Heating scheme

The Lerwick scheme appears to be available in RdSAP – it can certainly be selected, but when selected, the RdSAP software tested stated^[34] it did not recognise this data in the context of an RdSAP assessment. This may be a software bug, or it may reflect that the necessary data items are not fully implemented within the RdSAP software yet.

The type of data needed within a full SAP type assessment could use the approach of Display Energy Certificates, whereby the necessary data was collated and put on display outside the boiler house.