Evaluation at the Couple Building-System Level

The energy performance of a building [22] shall be expressed in a transparent manner and shall include an energy performance indicator and a numeric indicator of primary energy use based on primary energy factors per energy carrier, which may be based on national or regional annual weighted averages or a specific value for on-site production.

The energy performance indicator is energy class of the building, which by Energy Performance Certificates (EPCs) give information only on building prop­erties, resulting in energy needs (used).

For the mCCHP system, the energy efficiency indicator indicate conversion efficiency on the system and the PES indicator indicate the percentage of fuel saved from the energy production of the CCHP system compared to the same energy produced by the reference system, without indicating the share of renewable energy.

The new numeric indicators of primary energy use refer to specific value for on­site production and the share of renewable energy.

A new generation of EN standards [23] for implementing the Energy Perfor­mance of Building Directive introduced a clear distinction, between renewable and nonrenewable primary energy. In this sense was defined for assessment of energy performance of building, the two new indicators namely:

• integrated energy performance of building, Ep, tot;

• share of renewable or Renewable Energy Ratio (RER).

The integrated energy performance of building depends on:

• building properties, resulting in a value of the energy need;

• technical systems losses, resulting in a required delivered/exported energy;

• weighting of the delivered energy.

The integrated energy performance of building is calculated as difference between weighting of delivered energy and exported energy per energy carrier.

Total energy performance of building (Ep, tot) is the sum of the nonrenewable (Ep, nren) and renewable energy performance (EP;len) by following equation:

Ep, tot Ep, nren + Ep ,ren (69)

By renewable energy use for buildings, the new standard defines the ratio between renewable and total integrated energy performances, namely share of renewable or Renewable Energy Ratio (RER) by equation:

E

RER = – p^ren .100 % (70)

Ep, tot

In this way was introduced a clear distinction, between renewable and non­renewable primary energy and their connection with the total primary energy factor, to support renewable energy share evaluation. This is possible by introduce the final weighting factor namely primary energy conversion factors to define the integrated energy performance of buildings, so:

where:

• Ep—The primary energy demand,

• Edelji’—final energy demand of energy carrier i,

• fp;del;i—primary energy factor for demand energy carrier i,

• Eexp;i—exported final energy of energy carrier i,

• fp;exp;i—primary energy factor for export energy carrier i,

• i —the current number of the carrier.

For electricity delivered/exported, the primary energy factor is shown in Table 39.

The primary energy weighting is done depends of the fuel type and have the values given in the Table 40.

In the structural model 1 the electrical energy is produced by two sources: the Stirling engine and the photovoltaic source (PV panel) while the thermal energy is produced by three sources: Stirling engine, a boiler and a ST panel.

Table 40 Primary energy factors [24] Type of the energy supplier Primary energy factor Renewable fp. ren. Non-renewable-fp. nren Total fp. tot District heat/nearby 0 1.3 1.3 Grid electricity 0.2 2.3 2.5 Solar thermal 1 0 1 Photovoltaics 1 0 1 Bio gas 0.2 0.9 1.1 Natural gas 0 1.1 1.1

The results of evaluation with the new numeric indicators of primary energy use at the couple building-system level if the building is off-grid or on-grid (for elec­tricity connection) are shown in Tables 41 and 42.

Table 41 Case 1—Structural model 1 type off-grid Energy used (kWh/ m2 year) Delivered energy (kWh/ m2 year) fp. ren Ep. ren (kWh/ m2 year) fp. nren Ep. nren (kWh/ m2 year) fp. tot Ep. tot (kWh/ m2 year) Electrical 40.00 PV 24.42 1.00 24.42 0.00 0.00 1.00 24.42 CHP unit 15.54 0.00 0.00 1.10 17.09 1.10 17.09 Thermal 110.00 ST 50.29 1.00 50.29 0.00 0.00 1.00 50.29 CHP 46.63 0.00 0.00 1.10 51.29 1.10 51.29 Back-up 22.49 0.00 0.00 1.10 24.74 1.10 24.74 Exported energy 0.00 On site 0.20 0.00 2.30 0.00 2.50 0.00 Energy performance indicator of building Ep. ren 74.71 Ep. nren 93.13 Ep. tot 167.84 Renewable energy ratio RER [%] 44.51

	Energy used (kWh/ m2 year)	Delivered energy (kWh/ m2 year)	fp. ren	Ep. ren (kWh/ m2 year)	fp. nren	Ep. nren (kWh/ m2 year)	fp. tot	Ep. tot (kWh/ m2 year)
Electrical	40.00
PV		58.46	1.00	58.46	0.00	0.00	1.00	58.46
CHP unit		5.36	0.00	0.00	1.10	5.90	1.10	5.90
Thermal	110.00
ST		50.29	1.00	50.29	0.00	0.00	1.00	50.29
CHP		16.07	0.00	0.00	1.10	17.68	1.10	17.68
Back-up		45.45	0.00	0.00	1.10	50.00	1.10	50.00
Exported energy	23.82	On site	0.20	4.76	2.30	54.79	2.50	59.55
Energy performance indicator of building	Ep. ren	103.99	Ep. nren	18.78	Ep. tot	122.77
Renewable energy ratio	RER	%	–	–	–	84.70

Fig. 48 Renewable energy ratio of the structural models

Evaluation at the couple building-system level for the set of potential structural models (from model 1 to model 6) if the mCCHP system work off-grid. showed as in terms of renewable energy ratio the model 1 is the best. The share of renewable energy for these models is shown in Fig. 48.