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Reducing AHU energy consumption by a new layout of using heat recovery units

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Abstract

In this study, a new design for energy recovery from the return air has been introduced to improve the air handling unit (AHU) performance through the energetic analysis. The main objective is defined as the reduction in cooling and heating coils energy demand. In the novel AHU, the coldness from the exhaust air is transferred to the fresh air through the primary heat exchanger to reduce the cooling coil energy usage, while in the secondary heat exchanger, the warmness from the return air is recovered to the outlet cold air of the cooling coil to reduce the heating coil energy usage. Results showed that using air-to-air heat exchanger in hot and dry climate regions, the total energy consumption decreased up to 26.38%, which in turn increased the first law efficiency up to 35.84%, while in hot and humid climate these figures are 13.11% and 10.57%, respectively. It is concluded that the effect of using the air-to-air heat exchangers in hot and dry climate has priority over the hot and humid one.

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Abbreviations

A:

Area \(\left( {{\text{m}}^{2} } \right)\)

\(c\) :

Specific heat \(\left( {{\text{J}}\;{\text{kg}}^{ - 1} \,{\text{K}}^{ - 1} } \right)\)

\(C\) :

Heat capacity rate \(\left[ {C = \dot{m}c} \right]\)\(\left( {{\text{W\,K}}^{ - 1} } \right)\)

\(C^{*}\) :

Capacitance rate ratio

\(C_{\text{s}}\) :

Effective specific heat \(\left( {{\text{J}}\;{\text{kg}}^{ - 1} \,{\text{K}}^{ - 1} } \right)\)

\(\dot{E}\) :

Power \(\left( {\text{W}} \right)\)

FER:

First efficiency ratio

h :

Enthalpy \(\left( {{\text{J}}\;{\text{kg}}^{ - 1} } \right)\)

\(h_{\text{s}}\) :

Supply air enthalpy

\(\dot{m}\) :

Mass flow rate \(\left( {{\text{kg}}\,{\text{s}}^{ - 1} } \right)\)

\(\dot{m}_{\text{s}}\) :

Supply air mass flow rate \(\left( {{\text{kg}}\,{\text{s}}^{ - 1} } \right)\)

\(\dot{m}_{\text{f}}\) :

Fresh air mass flow rate \(\left( {{\text{kg}}\,{\text{s}}^{ - 1} } \right)\)

\(\dot{m}_{\text{r}}\) :

Return air mass flow rate \(\left( {{\text{kg}}\,{\text{s}}^{ - 1} } \right)\)

\(\dot{m}_{\text{c}}\) :

Cold water mass flow rate \(\left( {{\text{kg}}\,{\text{s}}^{ - 1} } \right)\)

PENR:

Percent of energy recovery

Q :

Power (W)

\(Q_{\text{S}}\) :

Sensible heat transfer rate

\(\vartheta\) :

Specific volume \(\left( {{\text{m}}^{ 3} \,{\text{kg}}^{ - 1} } \right)\)

RPR:

Required power ratio

T :

Temperature (K)

\(T_{\text{c}}\) :

Cooling water temperature (K)

\(T_{\text{o}}\) :

Ambient temperature (K)

\(T_{\text{s}}\) :

Supply air temperature (K)

\(\varphi\) :

Relative humidity

\(\omega\) :

Humidity ratio \(\left( {{\text{kg}}_{\text{v}} \;{\text{kg}}_{\text{a}}^{ - 1} } \right)\)

\(\varepsilon\) :

Effectiveness

cc:

Cooling coil

ci:

Chilled water inlet

co:

Chilled water outlet

cond:

Condensation

cw:

Chilled water

dew:

Dew point

f:

Fluid

h:

Heating coil

hi:

Hot water inlet

ho:

Hot water outlet

hw:

Hot water

max:

Maximum

min:

Minimum

mix:

Mixing box

o:

Ambient

pr:

Primary heat exchanger

r:

Conditioned space

se:

Secondary heat exchanger

sat:

Saturation

t:

Total

v:

Vapor

w:

Water

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Authors and Affiliations

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

    Rasool Kalbasi

  2. Department of Mechanical Engineering, Kermanshah University of Technology, Kermanshah, Iran

    Amin Shahsavar

  3. Laboratory of Magnetism and Magnetic Materials, Advanced Institute of Materials Science, Ton Duc Thang University, Ho Chi Minh City, Vietnam

    Masoud Afrand

  4. Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City, Vietnam

    Masoud Afrand

Authors
  1. Rasool Kalbasi
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  2. Amin Shahsavar
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  3. Masoud Afrand
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Correspondence to Masoud Afrand.

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Kalbasi, R., Shahsavar, A. & Afrand, M. Reducing AHU energy consumption by a new layout of using heat recovery units. J Therm Anal Calorim 139, 2811–2820 (2020). https://doi.org/10.1007/s10973-019-09070-2

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  • DOI: https://doi.org/10.1007/s10973-019-09070-2

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