Page 261 - Defrosting for Air Source Heat Pump

256 Defrosting for Air Source Heat Pump

defrosting performance were experimentally examined and quantitatively evaluated.
For a traditional ASHP unit, if the outdoor coil was enlarged by 50%, the MES effects
were changed from positive (0.33%) to negative ( 2.18%). For a novel ASHP unit,
the MES effects changed from 0.44% to 3.67%. The negative value suggested
more cold energy stored in the outdoor coil metal, and thus certain energy ta the
ken from indoor air should be first used to balance the stored energy; (3) The melted
frost effect on MES was analyzed. After the melted frost was taken away during
defrosting by installing water-collecting trays under each circuit in an multicircuit out-
door coil, the MES effects on defrosting performance for an ASHP unit could be
increased; and (4) Indoor thermal comfort during defrosting was discussed when using
an ASHP unit for space heating and the discussion results could help further optimize
a defrosting operation.
References

[1] Cole RA. Refrigeration loads in a freezer due to hot gas defrost and their associated costs.
ASHRAE Trans 1989;95(1):1149–54.
[2] Krakow KI, Lin S, Yan L. An idealized model of reversed-cycle hot gas defrosting of
evaporators, Part 1: Theory. ASHRAE Trans 1993;99(2):317–28.
[3] Krakow KI, Lin S, Yan L. An idealized model of reversed-cycle hot gas defrosting of
evaporators, Part 2: Experimental analysis and validation. ASHRAE Trans 1993;99
(2):329–38.
[4] Kim JH, Braun JE, Groll EA. A hybrid method for refrigerant flow balancing in multi-
circuit evaporators: upstream versus downstream flow control. Int J Refrig 2009;32
(6):1271–82.
[5] Kim JH, Braun JE, Groll EA. Evaluation of a hybrid method for refrigerant flow balancing
in multi-circuit evaporators. Int J Refrig 2009;32(6):1283–92.
[6] Wang ZH, Wang FH, Ma ZJ. Numerical study on the operating performances of a novel
frost-free air-source heat pump unit using three different types of refrigerant. Appl Therm
Eng 2017;112:248–58.
[7] Qu ML, Xia L, Deng SM, Jiang YQ. A study of the reverse cycle defrosting performance
on a multi-circuit outdoor coil unit in an air source heat pump-Part II: Modeling analysis.
Appl Energ 2012;91:274–80.
[8] Dong JK, Deng SM, Jiang YQ, Xia L, Yao Y. An experimental study on defrosting heat
supplies and energy consumptions during a reverse cycle defrost operation for an air
source heat pump. Appl Therm Eng 2012;37:380–7.
[9] Song MJ, Deng SM, Xia L. A semi-empirical modeling study on the defrosting perfor-
mance for an air source heat pump unit with local drainage of melted frost from its
three-circuit outdoor coil. Appl Energ 2014;136:537–47.
[10] Song MJ, Xia L, Deng SM. A modeling study on alleviating uneven defrosting for a ver-
tical three-circuit outdoor coil in an air source heat pump unit during reverse cycle
defrosting. Appl Energ 2016;161:268–78.
[11] Qu ML, Xia L, Deng SM, Jiang YQ. Improved indoor thermal comfort during defrost with
a novel reverse-cycle defrosting method for air source heat pumps. Build Environ 2010;45
(11):2354–61.
[12] Dong JK, Deng SM, Jiang YQ, Xia L, Yao Y. An experimental study on defrosting heat
supplies and energy consumptions during a reverse cycle defrost operation for an air
source heat pump. Appl Therm Eng 2012;37:380–7.