Available online at ScienceDirect. Energy Procedia 101 (2016 )

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1 Available online at ScienceDirect Energy Procedia 101 (2016 ) st Conference of the Italian Thermal Machines Engineering Association, ATI2016, September 2016, Turin, Italy Analysis of the coupling between CHP and EHP in an office building applied to the Italian energy market Sandro Magnani a *, Piero Danti a, Lorenzo Pezzola a a Yanmar R&D Europe, Viale Galileo 3/A, Florence 50125, Italy Abstract The increasing need for energy and cost efficient solutions for thermal and electric supply is giving new life to CHP plants, even for small power sizes. It is renowned that the optimal application of a CHP plant is to satisfy as much as possible both the electricity and the thermal requirements of the loads, but the frequent applicative context, especially for residential and/or tertiary buildings, is unbalanced towards the thermal needs, so that the sizing of the CHP is determined by the electric loads, at least in the Italian tariff structure context, with the consequence that the generator is relatively small and, consequently, the installation costs represent a consistent part of the capital investment. The increasing level of the performance of the electric heat pump can sensitively minimize the former issue: the combination between a CHP and an EHP can led to a larger size of the co-generative unit, whose exceeding power output can feed the heat pump so that to efficiently satisfy most of the thermal loads of the plant. In this paper an application case referred to an office building is presented: the optimal size of the system will be discussed, and the economic results (in terms of PBT and NPV) of the management of the plant compared with other commonly exploited solutions: Conventional supply, with the heat produced by a gas boiler, the cooling from an electric chiller, and the electricity purchased by the grid; Optimal sizing of the CCHP based on the heating loads duration curve, with the engine operated in thermal-led; Optimal sizing of the CCHP based on the electric loads duration curve, with the engine operated in power-led. The environment performance will be discussed as well, focusing on the comparison between the different solutions in terms of equivalent CO 2 emissions and primary energy consumptions The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the Scientific Committee of ATI Peer-review under responsibility of the Scientific Committee of ATI Keywords: CHP; cogeneration; EHP; design optimization; energy efficiency; CO 2 reduction * Corresponding author. Tel.: /5; fax: ;. address: sandro_magnani@yanmar.com The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the Scientific Committee of ATI doi: /j.egypro

2 Sandro Magnani et al. / Energy Procedia 101 ( 2016 ) Introduction In recent times, the level of the CO 2 concentration in the atmosphere has increased to a level that may determine remarkable changes in the climate. If no modifications to energy use and production will happen in the next future, this trend is going to become more and more detrimental for human activities: with this focus in mind, the developed and growing Countries are taking measures to minimize the carbon footprint of their activities (e.g. the European policy of the target [1] or the recent results of 2015 Paris Cop21 conference [2]), with interventions spacing in all energy-related fields. Particular attention is payed to the decrease of the energy consumption in buildings, coupled with the increase in the efficiency of their energy supply pieces of equipment: as reported in [3] they are one of the largest voices in the energy consumption in Europe, representing about 27% of the total final use. One of the options to minimize building carbon footprint stands in the adoption of efficient technologies for room conditioning: the spread of micro-combined Heat and Power (CHP) systems (also suggested by the COGEN Europe Response document [4]) and the improvement of the performance of Electric Heat Pumps (EHPs), whose diffusion is remarkably increased in the last years, can give promising results if widely adopted. The correct integration of these two types of devices can enhance the respective benefits, leading to a decrease in the environmental footprint of the households consumptions and in the reduction of the O&M costs of the buildings energy supply systems. In the following, an example of the integration between μ-chp and EHP systems will be analyzed: in paragraph 2 the details of the energy consumptions of the considered case study will be described, as well as the economic conditions applied to the Italian energy market. The results of the performance of the hypothesized configurations, in economic (Pay-Back Time PBT and Net Present Value NPV) and environmental (CO 2 emissions and primary energy consumptions) terms will be presented in part 4, with the main conclusions summarized in paragraph 5. Nomenclature CAR Cogenerazione ad Alto Rendimento CCHP Combined Cooling, Heating and Power CHP Combined Heating and Power COP Coefficient Of Performance EER Energy Efficiency Ratio EHP Electric Heat Pump ELF Electric Load Following ICE Internal Combustion Engine NPV Net Present Value PBT Pay-Back Time PES Primary Energy Saving TEE Titoli di Efficienza Energetica TLF Thermal Load Following 2. Problem definition 2.1. Definition of the case study For the present analysis, an office building is considered as the case study. The load profiles for this context are retrieved by Macchi et. al in [5], giving indications on the energy consumptions during two example days, one for the winter period and the other one for the summer time. The considered data are shown in Fig. 1. The reference day load profiles are furtherly elaborated on both monthly and daily basis to consider the differences in the energy use, especially on heating and cooling, when the environmental conditions are modified and the building has a different use during holiday periods. To assess the typical consumptions during the months of the year, the profiles are shifted on the basis of the monthly energy ratios shown in Table 1, derived from [5]. About holidays, an estimation of working days, pre-holidays, and holidays is carried out for each month, allowing to consider the different consumptions in contexts like offices, where holidays demand is very low, if null. The details of this division are reported in Table 2.

3 560 Sandro Magnani et al. / Energy Procedia 101 ( 2016 ) a b Fig. 1. Office building load profiles for the example winter day (a) and summer day (b). Table 1. Energy use correction coefficients for each month of the year. Load Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Electricity Heating Cooling Table 2. Days type for each month of the year. Day type Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec TOT Working Pre-holiday Holiday The loads for working days are estimated as the same as winter and summer days with the monthly correction factor. Pre-holidays are considered equal as the working days for the first half of the day, while for the second half a base electric load is considered (i.e. the night consumption); in summer the air conditioning system is considered switched off (i.e. the cooling load is null), while the room heating in winter is assumed to be half of the average night demand. For holidays the electric load is assumed to be as the second half of pre-holidays, the cooling loads in summer are always considered null, and the heating demand is considered as the second half of pre-holidays. The summary of the energy consumptions of the considered case study are summarized in Table 3. Table 3. Case study characteristics. Parameter Unit of measurement Value Building volume m 3 6,000 Electricity peak (year) kw e 37.8 Heating peak (winter) kw th 78.0 Cooling peak (summer) kw c 61.8 Yearly electricity request kwh e 137,954 Yearly heating request kwh th 150,447 Yearly cooling request kwh c 35,527 In the analysis, the energy loads are supposed to be satisfied by 4 different plant configurations: BASE: the heating loads are satisfied by a natural gas condensing boiler, while the cooling request is matched by an electric chiller; the power grid connection supplies all the electricity needs; CCHP-TLF: the plant is equipped with a micro-chp system coupled with an absorption chiller, operated with a thermal-led logic (Thermal Load Following, TLF), i.e. trying to satisfy the heating request during winter time and the cooling needs in summer; the mismatching between the output from

4 Sandro Magnani et al. / Energy Procedia 101 ( 2016 ) the tri-generation system and the energy request is satisfied by a natural gas condensing boiler, an electric compression chiller and the external power grid for heating, cooling and electricity respectively; CCHP-ELF: again, a micro-chp coupled with an absorption chiller is considered, with the management logic aiming to satisfy as much as possible the electric requests (Electric Load Following, ELF); the fulfillment of thermal loads is ensured by back-up systems, i.e. a natural gas condensing boiler and an electric compression chiller; additional electric requests are satisfied by the external power grid; CCHP+EHP: a tri-generation system is coupled with an electric heat pump, this latter one providing to close the thermal balance of the plant; the CCHP management considers two different aspects, maximizing the efficiency of the tri-generation system and avoiding the sale of the exceeding electricity to the grid because of the poor remuneration; the CCHP is thus operated in TLF until the electric balance with the grid reach the null value: if the thermal request is not satisfied, the EHP is enabled, with an increase in the electric demand of the building, balanced by an increase of the output of the CCHP, with a larger thermal output; the procedure iteratively considers the two aspects until a perfect balance between the electric and thermal request is reached (see the flow chart in Fig. 2). Fig. 2. CCHP operation strategy for CCHP+EHP configuration. The size of the back-up systems, i.e. of the gas boiler, of the electric chiller, and of the heat pump, is determined by the peak request of the loads and is established once for all the different plant scenarios. The size of the tri-generation system is different for each configuration. For the standards operation strategy for the CCHP system (i.e. TLF and ELF) the method of the maximum rectangle area of the cumulative load curve is considered: all the yearly loads are ordinated from the maximum to the minimum value, and their correspondent time duration is also plotted, determining the loads duration curve; the ideal size of the engine is defined by the power reference of the vertex lying on the curve determining the subscribed rectangle with the largest area possible. By doing so, the number of operating hours of the system at rated power (at the maximum efficiency) is maximized, and a consistent part of the loads with smaller power values can also be covered, as shown in Fig. 3 (a) for the CCHP-TLF case and in Fig. 3 (b) for the CCHP-ELF case. Two different loads are considered for the CCHP-TLF and CCHP-ELF sizing method: the generator power output for the former one is determined by considering the thermal loads, i.e. the heating loads in winter period and the equivalent heating loads for the summer time, by multiplying the cooling loads for a fixed conversion coefficient representing the average conversion efficiency of the absorption chiller; similarly, for the CCHP-ELF case the loads considered are the electric ones. As a consequence, in CCHP-TLF case, the estimated ideal size of the PM results in 15.3 kw th : by the analysis of Yanmar micro-chp catalogue, the closest option is the CP10WE1 model, with a rated electric output of 10 kw e, corresponding to 16.2 kw th. When considering CCHP-ELF configuration, the theoretical best size of the cogeneration system results 31.8 kw e : the Yanmar product with the closest output is the CP35VC model, with a rated power output of 35 kw e and a heat recovery of 52.2 kw th. Both systems are based on a gas-fed Internal Combustion Engine (ICE), with an inverter and capable of a maximum output temperature of 85 C, compliant with the energy characteristics requested by the office building. No general rule exists for the definition of the ideal size of the CHP for the CCHP+EHP configuration. The power output of the tri-generation system is so determined by a simplified consideration by the authors: the sum of the rated thermal output and the conversion of half of the rated power of the ICE (needed for feeding the electric heat pump) shall be as closest as possible to the

5 562 Sandro Magnani et al. / Energy Procedia 101 ( 2016 ) heating peak load. As a consequence the selected option is the Yanmar CP25WE, with a rated electric output of 25.1 kw e and a maximum heat recovery capacity of 38.4 kw th. The size of the generators and their characteristics are reported in Table 4 and Table 5, respectively. a b Fig. 3. (a) equivalent heating loads duration curve for CCHP-TLF sizing; (b) electric loads duration curve for CCHP-ELF sizing. Table 4. Equipment size for the considered configurations. Equipment BASE CCHP - TLF CCHP - ELF CCHP + EHP CHP [kw e] N.A Absorption chiller [kw c] N.A Gas boiler [kw th] N.A. Electric chiller [kw c] N.A. EHP [kw th]/[kw c] N.A. N.A. N.A. 80/70 Table 5. Equipment performance. Equipment Rated output [kw] Min output [kw] Rated efficiency CP10WE1 electric % CP10WE1 heating % CP25WE electric % CP25WE heating % CP35VD electric % CP35VD heating % Gas boiler % Electric chiller (EER) EHP heating (COP) EHP cooling (EER) Absorption chiller (EER) The size of the absorption chiller is determined by considering the rated thermal output of the Yanmar CHPs and multiplying this value for a fixed reference conversion factor for the chiller, estimated in 0.7. The lower output of the Yanmar micro-chp systems is also considered: if the power request is under the technical limit, the system is not run, and the back-up generators (or the power grid) satisfy the requests. The partial load performance of all the generators are considered as well: for Yanmar products, the global efficiency is constant in all the operating range, with the electric efficiency slightly decreasing in favor of the thermal efficiency, like in [6]. The gas boiler is considered with a constant efficiency, due to the negligible loss of efficiency at partial loads; the EHP and chiller partial load behavior is supposed to be as in [7], while for the absorption chiller data in [8] is considered; for sake of simplicity, no dependency of the performance on the external temperature is considered.

6 Sandro Magnani et al. / Energy Procedia 101 ( 2016 ) Definition of the energy market context The economic analysis results are strongly affected by the energy market context. In this particular case, the Italian scenario is selected as the reference one. The purchase of the electricity from the grid is characterized by three different markets: the so called Mercato di maggior tutela, whose tariffs are defined and updated by the Italian Authority for Electricity, Natural Gas and Hydric System (AEEGSI, Autorità per l Energia Elettrica, il Gas ed il Sistema Idrico), the Mercato libero, whose tariffs are directly negotiated with the electric companies on the basis of different contracts (the only possible for large customers and optional for small and medium consumer), and the Mercato di salvaguardia, to which each customer not belonging to the others refer to. In this case, the most common one is selected, the Mercato di maggior tutela, with different electricity prices on the basis of the time of the day and of the day of the week. Three segments are individuated: F1 from Monday to Friday from 8 AM to 7 PM; F2 from Monday to Friday from 7 AM to 8 AM and from 7 PM to 11 PM, and on Saturdays from 7 AM to 11 PM; F3 from Monday to Friday from midnight to 7 AM and from 11 PM to midnight, and on all Sundays. In addition to consumptions variable costs, fixed costs are also due, comprehensive of the connection charge (based on the maximum power supply), of the system operation charges and of taxes: these latter contributions represent between 50% and 70% of the total electric bill. Also the natural gas market can be divided into 3 types, but in this case the prices are flat during all the day and week. Again, other charges are due, with the pure energy component being from 40% to 60% of the total amount. For the presented case study, subsidies for CHP are also due to be considered, defined as Cogenerazione ad Alto Rendimento (CAR, high efficiency cogeneration) and whose reference is in [9]: Italian laws allow a reduction on taxes for natural gas if the operation of co-generator achieves two different thresholds: the global efficiency of the systems, that for micro-chps (< 50 kw e ) shall be larger than 75%, and the Primary Energy Saving (PES), that shall be at least 0 (an advantage in terms of primary energy use is achieved compared to the separated production). If both parameters are satisfied, a reduction of the natural gas price of about 33% is experienced. In addition, CHPs also benefit of the Titoli di Efficienza Energetica TEE (energy efficiency certifications): the system is assigned of 1 TEE when 1 MWh of primary energy is saved by the system. At present their value is about 100, but their future is not clear and their contribution is so neglected. 4. Results and discussion In addition to the energy market considerations in paragraph 2, for the economic and environmental estimation the considered additional parameters are summarized in Table 6. From the energy side, in winter period the cogeneration system can cover almost completely the energy needs in case of CCHP-ELF configuration (also wasting part of the recovered heat), while the percentage are reduced to about 44% of the electric needs and to a percentage variable from 55% to more than 70% of the heating demand for the CCHP-TLF and CCHP+EHP scenarios. A similar behavior is also experienced during the summer period, when CP25WE and CP35VD are installed, while the CP10WE1 shows a remarkable reduction in the total energy supply, covering about 1/4 of the electric load and 1/3 of the cooling one, due to the small rated output. All the details are shown in Table 7, with an estimation of both the equivalent and effective operating hours of the CHPs in the year. In terms of economic results, the configuration CCHP+EHP shows the better performance during most of the year, except than in mid-season months, when the CCHP-TLF is preferable. This may be attributable to the lower thermal request characterizing the mentioned periods: for supplying the loads the CP25WE shall operate in partial load conditions with a limited electric efficiency, while the CP10WE1 is close to the rated output, with a lower gas need and a larger electric production, with two beneficial effects: a saving both in natural gas and electricity from the grid. The details of the economic results for each month are shown in Table 8 for all the plant configurations. The CCHP-ELF is preferable than the CCHP-TLF during the periods with a larger thermal request: the possibility to supply much of the thermal load and to minimize the purchase from the grid determine this result, even if in some cases part of the heat is wasted and the natural gas cost can no longer benefit of the fiscal discount. In all the other periods the strategy for the CP35VD is not convenient compared to the other CCHP solutions, because the higher natural gas price due to the heat waste (causing the non-achievement of the efficiency and PES thresholds for the fiscal benefit) is not balanced by the larger electric production.

7 564 Sandro Magnani et al. / Energy Procedia 101 ( 2016 ) Table 6. Economic and environmental calculation parameters. \ Value Parameter Value Electricity price F1 [ /kwh e] EHP reference cost [ /kw c] 450 Electricity price F2 [ /kwh e] Gas boiler reference cost [ /kw th] 150 Electricity price F3 [ /kwh e] Electric chiller reference cost [ /kw c] 300 Electricity selling price [ /kwh e] 0.03 CHP maintenance cost [ /h ON] (absorption chiller included) 0.30 (CP10WE1) 0.40 (CP25WE) 0.50 (CP35VD) Natural gas price [ /Sm 3 ] 0.78 EHP maintenance cost [ /h] 0.10 Italian power grid reference efficiency [%] 46 Gas boiler maintenance cost [ /h] 0.07 Natural gas CO2 emission factor [kg/sm 3 ] Electric chiller maintenance cost [ /h] 0.07 Italian grid CO2 emission factor [ /kwh e] Installation cost [ ] 7,000 (3,000 for BASE) CHP reference cost [ /kw e] 1,500 Rate of interest [%] 3.0 Absorption chiller reference cost [ /kw c] 700 Inflation rate [%] 1.0 Table 7. Yearly energy performance of the considered plant configurations. Plant layout Winter Summer E el CHP E th CHP E el backup h eq CHP h CHP E el CHP E th CHP E el backup h eq CHP h CHP CCHP-ELF 98.3 % % n.a. 3,310 5, % % 5.5 % 1,519 1,864 CCHP-TLF 44.7 % 55.9 % n.a. 5,266 5, % 39.2 % 23.6 % 1,631 1,788 CCHP+EHP 43.2 % 72.4 % 9.9 % 2,338 3, % 70.2 % 7.5 % 1,293 1,446 Table 8. Monthly and yearly economic performance of the considered plant configurations (all values in ). Plant layout Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec TOT BASE 3,895 4,117 3,734 3,393 3,093 3,194 3,865 1,768 3,094 3,489 3,763 4,262 41,667 CCHP-ELF 2,905 3,131 3,287 3,193 2,964 2,305 2,708 1,215 2,939 3,192 3,077 3,177 34,091 CCHP-TLF 3,235 3,421 3,009 2,805 2,569 3,193 3,538 1,708 2,918 2,797 3,042 3,558 35,795 CCHP+EHP 2,252 2,581 3,163 3,012 2,814 2,275 2,314 1,115 2,465 2,999 2,732 2,616 30,339 The NPV for all the hypothesized configurations, considering as reference the configuration BASE, is shown in Fig. 4. Due to the uncertainty on the future perspective of the presence and value of the TEE, their contribution is neglected in the yearly evaluations. By the analysis of the results, an evaluation of the more suitable installation based on the PBT only would bring to misleading results, because both solutions CCHP+EHP and CCHP-TLF present the return of the investment in the same period (about 5 years), but remarkably higher investment costs. The larger economic saving of the previous one compared to the other brings to a larger advantage during the rest of the life span of the tri-generation system, estimated in 15 years. On the other side, the CCHP-ELF solution would determine a longer PBT, with the NPV value becoming positive after about 11 years, a time period too large for the suitability of the investment. The analysis of the environmental footprint, in terms of equivalent CO 2 emissions and primary energy consumption, of the proposed plant layouts partially confirms the economic results, as shown in Fig. 5. The cleanest solution is the CCHP+EHP with the CCHP-TLF ranked as second, with a decrease of 10% and 9.7% in CO 2 and primary energy respectively for the former one (more than 9 t of CO 2 and 45 MWh per year), while the advantage for the other is respectively 6.5% and 6.2% (a decrease of about 6 t of CO 2 and 28 MWh). The CCHP-ELF presents the worst emissions and the largest primary energy consumption of the analyzed layouts, also worse than the BASE solution. This behavior may be attributable to the large amount of wasted heat, due to the CCHP management logic, giving advantages from the economic but not from the environmental point of view.

8 Sandro Magnani et al. / Energy Procedia 101 ( 2016 ) Fig. 4. NPV results for the considered plant configurations. a b Fig. 5. (a) yearly CO 2 emission results; (b) yearly primary energy consumptions. 5. Conclusions The reduction of energy consumptions and the increase of efficiency in buildings are the focus of the next future for developed and growing Countries: the use of micro-chp and EHP systems can help to achieve these targets. Considering an office building as the case study in the Italian energy market scenario, 4 different solutions for supplying the energy request are analyzed: the conventional layout with the heat supplied by a gas boiler, the cooling by an electric chiller and the power from the external distribution grid; three different micro-cchp based solutions, the first one with the CCHP sized on thermal demand and managed with a thermal-led strategy, the second one with the CCHP sized on the electric loads and with the engine managed in power-led, and the combination of a CCHP with and EHP, managed so that to avoid the selling of electricity from the ICE to the grid. This last configuration shows the most promising results, in terms of both economic merit and environmental performance, with a decrease in the O&M costs of more than 25%, and an increase in the environmental performance (CO 2 emissions and energy consumptions) of about 10%. These results are mainly determined by the sizing of the CCHP, implying an integrated design between the two elements, and by the operation strategy of the engine, which does not allow the waste of the heat and avoids the power selling to the distribution grid, due to the low remuneration from the entity in charge of purchasing the exceeds of the distributed local electric generators. References [1] [2] [3] [4] [5] Macchi E, Campanari S, Silva P. La microcogenerazione a gas naturale. Polipress; In Italian [6] [7] In S, Cho K, Lim B, Lee C. Partial load performance test of residential heat pump system with low-gwp refrigerants. Applied Thermal Engineering 2015; pp , vol.85. [8] [9] In Italian.