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Dynamic model and response characteristics of liquid desiccant air-conditioning system driven by heat pump

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Abstract

The liquid desiccant air-conditioning system is considered as an energy-efficient alternative to the vapor compression system. The dynamic response characteristics of the system under variable cooling load play an important role in the air temperature and humidity control performance of the system. However, the dynamic response characteristics have not been fully revealed in previous studies. Thus, a dynamic model for a heat pump driven liquid desiccant air-conditioning (HPLDAC) system is established to investigate the dynamic response characteristics of the system in this study. Subsequently, experiments were conducted to validate the accuracy of the dynamic model. The simulation results show a good agreement with the experimental data. The simulation results reveal that evaporating water from the solution is a time-consuming process, compared to adding water to the solution. It spends a long time for the HPLDAC system to decrease the high relative humidity of supply air to a low value, which limits the air temperature and humidity control performance of the system. The upper band for the water replenishing value opening (Δφup) is a crucial parameter to improve the limitation. When Δφup decreases from 1.0% to 0.25%, the time consumed to reduce the supply air relative humidity to the new lower set value can be saved by 30.6%.

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Abbreviations

A :

heat transfer area (m2)

c p :

specific heat capacity of dry packing (kJ/(kg·K))

c s :

specific heat capacity of solution (kJ/(kg·K))

Gr :

Grashof number (—)

H :

height (m)

h :

enthalpy (kJ/kg)

h e :

enthalpy of air in equilibrium with liquid desiccant (kJ/kg)

K :

product of heat transfer coefficient and area (W/K)

k :

heat transfer coefficient (W/(m2·K))

l :

characteristic length (m)

Le :

Lewis number (—)

M :

mass (kg)

m :

mass flow rate (kg/s)

NTU :

number of heat transfer units

NTU m :

number of mass transfer units

Pr :

Prandtl number (—)

Q a :

cooling capacity obtained by process air (kW)

Q c :

heat capacity provided by condenser (kW)

Q e :

cooling capacity provided by evaporator (kW)

Re :

Reynolds number (—)

r :

vaporization latent heat of water (kJ/kg)

t :

temperature (°C)

W :

electricity consumption (kW)

X :

desiccant solution mass concentration (%)

ε :

heat transfer efficiency (—)

λ :

thermal conductivity (W/(m·K))

Ï„ :

time (s)

ω :

humidity ratio (g/kg)

ω e :

humidity ratio air in equilibrium with liquid desiccant (g/kg)

a:

air

c:

condenser

com:

compressor

e:

evaporator

fan:

fan

in:

inlet

out:

outlet

p:

packing

pump:

solution pump

s:

solution

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Acknowledgements

This research was supported by the National Key Research Program of China (No. 2018YFC0705202) and National Natural Science Foundation of China (No. 51638010).

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Authors and Affiliations

  1. Department of Building Science and Technology, Tsinghua University, Beijing, 100084, China

    Bowen Guan, Xiaohua Liu & Tao Zhang

  2. Department of Electrical and Electronic Engineering, University of Hong Kong, Hong Kong, 999077, China

    Andong Wang

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  1. Bowen Guan
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  2. Xiaohua Liu
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  3. Tao Zhang
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  4. Andong Wang
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Correspondence to Xiaohua Liu.

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Guan, B., Liu, X., Zhang, T. et al. Dynamic model and response characteristics of liquid desiccant air-conditioning system driven by heat pump. Build. Simul. 14, 1773–1784 (2021). https://doi.org/10.1007/s12273-021-0789-4

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  • DOI: https://doi.org/10.1007/s12273-021-0789-4

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