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Economic, exergy, and the environmental analysis of the use of internal combustion engines in parallel-to-network mode for office buildings

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Abstract

In recent times, the tendency toward the use of combined heat and power cogeneration systems to supply the electrical and heat requirements has provided the heat for the buildings in addition to the cost reduction of the power distribution networks. In this study, the Carrier Software per 15th of each month did the hourly analysis of heating, cooling, and electrical loads for a 5-floor office building with a net area of 1000 m2 (200 m2 per each floor) in Tehran City (in Iran) and besides the average loads in that month were assumed. The mechanical air-conditioning system with absorption chiller is used to supply the heating load in the second half of the year (the autumn and winter), the heat pump system and the cooling load in the first half of the year (spring and summer). Due to the average thermal, cryogenic, and electrical loads, the number of motors required for the parallel mode of the power distribution system was 4 and for the network-independent mode was 7. The results show that the annual productions of \(m_{{{\text{Co}}_{2} }} ,m_{\text{Co}} ,\;{\text{and}}\;m_{\text{No}}\) are 648,640, 21,395, and 68,172 kg/year, respectively. The entropy production in cogeneration mode was 801,861.120 kJ/kg year. Besides, the prices of electricity in parallel-to-network and network-independent modes were calculated as 0.96 and 0.4866 US$/kWh, respectively.

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Abbreviations

A :

Heat transfer area (m2)

C :

Constant equation 3

c f :

Capacity factor

\(\bar{c}\) :

Specific heat (J/kg K)

e :

Exergy (kJ/kg)

e :

Electrical power (kW)

e′:

Needed electrical power (kW)

h :

Heat convection coefficient (kJ/kg K)

i :

Interest rate (–)

I :

Amount of interest of loan (–)

k :

Heat conduction coefficient (W/mK)

L :

Effective life of the system (year)

LHV:

Lower heating value (kJ/kg)

M :

Molecular mass (kg)

\(\dot{m}\) :

Mass flow rate (kg/s)

n :

Number of heat and power cogeneration systems or moles (–)

P :

Pressure (kPa)

q :

Heat energy of output gases (kW)

Q :

Heating or cooling loads (kW)

q′ :

Heat energy needed for hot water (kW)

\(\bar{R}\) :

Universal gas constant (kJ/kmol K)

S :

Entropy (kJ/kg K)

\(\dot{S}\) :

Entropy generation (kW/kg K)

T :

Temperature (K or °C)

u :

flame expansion speed (m/s)

U :

Overall heat transfer coefficient (W/m K)

U :

Internal energy (kJ/kg)

V :

Volume (m3)

\(\dot{V}\) :

Daily water consumption volumetric (m3/s)

\(\dot{W}_{\text{net}}\) :

Electrical power (kW)

\(\bar{\rho }\) :

Average density of mixture (kg/m3)

β :

Effectiveness coefficient (–)

α :

Heat exchanger coefficient (–)

η :

Efficiency

A:

Social cost of air pollution

a:

Air

Abs:

Absorption chiller

b:

Combusted fuel mixture

c:

Cooling

C:

Cost

ch:

Chemical

cw:

Cooling water

CO:

Carbon monoxide

CO2 :

Carbon dioxide

e:

Electricity

f:

Fuel or flame front

gen:

Generation

h:

Heating

HP:

Heat pump

i:

Component

I:

Installation

IC:

Internal combustion

JHX:

Jacket heat exchanger

NO:

Monoxide nitrogen

O:

Operation and maintenance or ambient condition

ph:

Physical

ref:

Refrigerant

t:

Total or flame expansion

u:

Non-combusted mass

V:

Volume

W:

Consumed water

1:

Daily

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Author information

Authors and Affiliations

  1. Department of Mechanical Engineering, North Tehran Branch, Islamic Azad University, Tehran, Iran

    Saman Chegini

  2. Department of Mechanical Engineering, Pardis Branch, Islamic Azad University, Pardis New City, Iran

    M. A. Ehyaei

Authors
  1. Saman Chegini
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  2. M. A. Ehyaei
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Corresponding author

Correspondence to M. A. Ehyaei.

Additional information

Technical Editor: Jose A. R. Parise.

Appendices

Appendix 1: Tehran Weather Conditions

The mentioned office building is located in Tehran. The latitude of Tehran is 35.7°N and longitude is also considered − 51.4°. The height from the sea level is assumed as 1220 m for Tehran. The temperature of the dry-bulb and the wet-bulb in the summer are 38.9 and 23.9 °C, respectively.

The summer changes are also considered to be 15 °C, which is equal to the difference between the dry-bulb and the wet-bulb temperature in the summer. Similarly, the dry-bulb and the wet-bulb temperatures should also be defined in the winter. In this regard, the dry-bulb temperature in winter is considered to be − 6.6 °C, and also the wet-bulb temperature is considered to be − 8.7 °C. It should be noted that all the data are assumed according to the Mehrabad Meteorological Station. According to the software manual, the air quality index is assumed to 1. The average earth reflection coefficient is assumed to 0.14 and the thermal conductivity of soil is assumed to 1.385 W/mK. It is known that the time difference between Tehran and Greenwich is − 3.5 h. Another important issue that should be considered in the simulation of the building loads is the time difference. On the 30th of September, the same as each year, the official clock of the country would go back one hour and would go forward on the first day of April. Consideration for this issue for simulation of the building’s loads is essential. The monthly average global horizontal irradiance in different months of the year is shown in Fig. 12 [29].

Fig. 12
figure 12

Total global horizontal irradiance for different months of the year in Tehran City [29]

Full size image

As shown in Fig. 12, the highest solar radiation belongs to June, July, and August, which are equivalent to Khordad, Tir, and Mordad months in Iranian calendar. Also in Fig. 13, the average daily clearness amount can be seen [29].

Fig. 13
figure 13

Daily clearness amount for different months of the Gregorian calendar in Tehran City [29]

Full size image

As shown in Fig. 13, the daily clearness amount is generally higher for summer months. In fact, the daily clearness amount is affected by different factors such as pollutant and floating particles as well as cloudy and foggy air, and so on. Due to inversion, we know that in cold seasons, the number of air particles increase and as a result, the sky gets dusty and finally, the clearness amount would reduce. Moreover, the maximum and minimum average and absolute temperatures can be seen in Fig. 14 [29].

Fig. 14
figure 14

Dry-bulb temperature differences of Tehran City in different months of the year [29]

Full size image

As shown in Fig. 14, the maximum absolute is 40.5 °C, which was previously studied. The minimum absolute is about − 5 °C. It should be noted that the maximum dry-bulb temperature was assumed to be 38.9 °C. Since in the current situation, the maximum was calculated for the middle of the month, the maximum absolute can be taken for any day of the month, though. This could be the case for the minimum dry-bulb temperature [29]. Table 14 shows the maximum and minimum monthly temperature and solar radiation [29].

Table 14 Lowest and highest dry-bulb temperature and solar radiation [29]
Full size table

As shown in Table 14, the highest dry-bulb temperature can be feeling on July 14th, at 4:00 PM. Similarly, the lowest dry-bulb temperature can be feeling at 4:00 AM on July 7th. For solar radiation, the highest radiation occurs on July 18th, and the lowest radiation would be on July 20th. That is, the above amounts are the maximum and minimum in each month. By considering Tables 1, 2, and 3, it can be understood that in January, the highest dry-bulb occurs at 13:00. As the days get longer, the hour in which the maximum dry-bulb temperature feels is little delayed. In February, the maximum dry-bulb temperature feels at 14:00, and this process would almost continue. In the spring, the maximum dry-bulb temperature feels at 15:00. However, as summer is on the way, the maximum hour would forward to 16:00. As summer passed, the hour in the maximum dry-bulb temperature would reduce due to the days getting shorter and the change in position of the sun and its radiation. In autumn, it reaches 15:00 and then, 14:00 , and this cycle would go on.

Appendix 2: Method of calculation of IC engine units

By the use of Eqs. 27 and 28, and considering the following assumptions, the number internal combustion engine units can be calculated.

$$\beta_{\text{hp}} = 3, \quad \beta_{\text{ref}} = 2.5, \quad \beta_{\text{abs}} = 0.7, \quad \alpha = 0.8$$

For calculation of the heat energy needed for hot water consumed, it can be written by the use of Eq. 25:

$$q^{\prime} = 1\,\left( {{\text{kg}}/{\text{Lit}}} \right) \times 4.2\,\left( {{\text{kJ}}/{\text{kg}}\;^\circ {\text{C}}} \right) \times 2430\,({\text{Lit}}/{\text{day}}) \times 50\left( {^\circ {\text{C}}} \right) = 510300\,({\text{kJ}}/{\text{day}}) = 5.2 \;{\text{kW}}/{\text{day}}$$

The amount of the heating load needed for supplying the hot water in 1 h would be 0.21 kW. The calculations of the number of engines for heating, and parallel-to-network mode are as follows:

$$e^{\prime} = 50\, {\text{kW}},\quad Q_{h} = 150\;{\text{kW}}, \quad q^{\prime} = 0.21\,{\text{kW}},\quad q = 61.6 \;{\text{kW}}, \quad e = 30\;{\text{kW}}$$

Considering the above values in Eq. 27, the value of n is obtained as 2.15. In other words, the number of units needed for the system is equal to 3, based on the heating load needed for the building. For the cooling mode of the building, the values are as below:

$$e^{\prime} = 50 \,{\text{kW}},\quad Q_{\text{c}} = 220 \,{\text{kW}}, \quad q^{\prime} = 0.21\,{\text{kW}},\quad q = 61.6\,{\text{kW}}, \quad e = 30 \,{\text{kW}}$$

Considering the above values in Eq. 28, the value of n is obtained as 3.15. In other words, the number of units needed for the system is equal to 4, based on the cooling load needed for the building. By the comparison of this number with that of heating load, the basis for the number of the systems needed by the building would be the cooling load. As a result, in the parallel-to-network mode, 4 power and heat cogeneration systems would be needed.

The calculations of the number of the engines in network-independent mode are as follows:

$$e^{\prime} = 125.5\,{\text{kW}},\quad Q_{\text{h}} = 235\,{\text{kW}}, \quad q^{\prime} = 0.21\,{\text{kW}},\quad q = 61.6\,{\text{kW}}, \quad e = 30 \,{\text{kW}}$$

Considering the above values in Eq. 27 and for the heating mode, the value of n is obtained as 4.40. In other words, the number of units needed for the system is equal to 5, based on the heating load needed for the building. For the cooling load supply mode of the building, the values are as below:

$$e^{\prime} = 125.5\,{\text{kW}},\quad Q_{\text{c}} = 377\,{\text{kW}}, \quad q^{\prime} = 0.21\,{\text{kW}},\quad q = 61.6\,{\text{kW}}, \quad e = 30 \,{\text{kW}}$$

Considering the above values in Eq. 28, the value of n is obtained as 6.31. In other words, the number of units needed for the system is equal to 7, based on the cooling load needed for the building. As a result, in the network-independent mode, 7 power and heat cogeneration systems would be needed.

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Chegini, S., Ehyaei, M.A. Economic, exergy, and the environmental analysis of the use of internal combustion engines in parallel-to-network mode for office buildings. J Braz. Soc. Mech. Sci. Eng. 40, 433 (2018). https://doi.org/10.1007/s40430-018-1349-4

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