Method for predicting cooling load
View Patent ↗Disclosed is a method for predicting the cooling load for efficient operation of a heat accumulation system by obtaining a prediction function regarding outdoor air temperature and specific humidity from meteorological office data, predicting the outdoor air temperature and specific humidity by using the prediction function and the highest and lowest temperatures of the weather forecast, and predicting the cooling load based on the sensible heat load coefficient, outdoor air coefficient, sensible heat load constant, and latent heat load constant, which are obtained from the building design data. The cooling load can be predicted without using a complicated mathematical model and with no reference to past operation data regarding the target building, but solely based on four air-conditioning design values of the building and the highest and lowest temperatures of the next day, which can be easily obtained from the weather forecast of the meteorological office.
1. A method for predicting a cooling load of a cooling system for a building, comprising the steps of:
calculating, using the cooling system, a sensible heat load and a latent heat load, respectively, of solar radiation heat, conduction heat of the building, heat caused by infiltrated outdoor air and ventilated outdoor air of the building, and internally generated heat for every conditioned space of the building; and
adding the calculated sensible heat load and latent heat load to obtain the cooling load of the cooling system for the building so that the cooling system is run at the obtained cooling load, wherein the sensible heat load of the cooling load is calculated by
{dot over (Q)} s =P s ( T o −T i )+{dot over (m)} s ( h io −h i )(1−ε s )+ C s (1)
wherein,
{dot over (Q)} s is the sensible heat load,
P s is a sensible heat load coefficient,
{dot over (m)} a is an outdoor air coefficient,
C s is a sensible heat load constant,
T o is an outdoor air temperature,
T i is an indoor temperature,
h io is enthalpy of air at a point where an indoor specific humidity meets the outdoor air temperature on a psychrometric chart,
h i is enthalpy of air in an indoor condition, and
εs is a sensible heat recovery ratio of infiltrated and ventilated air, and
wherein the latent heat load of the cooling load is calculated by
{dot over (Q)} l ={dot over (m)} a ( h o −h io )(1−ε l )+ C l (2)
wherein,
{dot over (Q)} l is the latent heat load,
{dot over (m)} a is the outdoor air coefficient,
C l is a latent heat load constant,
h o is an enthalpy of air in an outdoor air condition,
h io is the enthalpy of air at the point where indoor specific humidity meets the outdoor air temperature on the psychrometric chart, and
ε l is a latent heat recovery ratio of infiltrated and ventilated air.
2. The method as claimed in claim 1 ,
(i) wherein the calculation by the equation (1) is performed by providing the sensible heat load coefficient P s to the cooling system for the building,
wherein the sensible heat load coefficient P s is obtained from
{dot over (Q)} s,d =P s ( T o,d −T i,d )+ {dot over (m)} a ( h io,d −h i,d )(1−ε s,d )+ C s (3)
wherein,
a design sensible heat load {dot over (Q)} s,d ,
the outdoor air coefficient {dot over (m)} a ,
the sensible heat load constant C s ,
an outdoor air design temperature T o,d ,
an indoor design temperature T i,d ,
an enthalpy h io,d of air at a point where indoor design specific humidity meets outdoor air design temperature on the psychrometric chart,
an enthalpy h i,d of air in an indoor design condition, and
a design sensible heat recovery ratio ε s,d of infiltrated and ventilated air
are obtained from given design specifications of the building and provided to the cooling system for the building, and
(ii) wherein the calculation by the equation (2) is performed by providing the latent heat load constant C l to the cooling system for the building,
wherein the latent heat load constant C l is obtained from
{dot over (Q)} l,d ={dot over (m)} a ( h o,d −h io,d )(1−ε l,d )+ C l (4)
wherein,
a design latent heat load {dot over (Q)} l,d ,
the outdoor air coefficient {dot over (m)} a ,
the enthalpy h o,d of air in the outdoor air design condition,
the enthalpy h io,d of air at the point where the indoor design specific humidity meets the outdoor air design temperature on the psychrometric chart, and
a design latent heat recovery ratio ε l,d of infiltrated and ventilated air
are obtained from the given design specifications of the building and provided to the cooling system for the building.
3. The method as claimed in claim 1 ,
(i) wherein the calculation by the equation (1) is performed by providing the sensible heat load coefficient P s the cooling system for the building,
wherein the sensible heat load coefficient P s is obtained from
{dot over (Q)} s,d =P s ( T o,d −T i,d )+ {dot over (m)} a ( h io,d −h i,d )(1−ε s,d )+ C s (5)
wherein,
a design sensible heat load {dot over (Q)} s,d ,
the outdoor air coefficient {dot over (m)} a ,
the sensible heat load constant C s ,
an outdoor air design temperature T o,d ,
an indoor design temperature T i,d , the enthalpy h io,d of air at a point where indoor design specific humidity meets the outdoor air design temperature on the psychrometric chart,
an enthalpy h i,d of air in an indoor design condition, and
a design sensible heat recovery ratio ε s,d of infiltrated and ventilated air
are obtained from given design specifications of the building and provided to the cooling system for the building, and
(ii) wherein the calculation by the equation (2) is performed by providing the latent heat load constant C l to the cooling system for the building,
wherein the latent heat load constant C l is directly obtained from the given design specifications of the building and provided to the cooling system for the building.
4. The method as claimed in claim 1 , wherein, in order to obtain the outdoor air temperature T o and the specific humidity necessary to calculate enthalpy of the outdoor air h o , the method further comprising the steps of
(i) setting a highest and a lowest temperatures of an average outdoor air temperature as 1 and −1, respectively,
(ii) obtaining a non-dimensional outdoor air temperature T*(h) by using the nondimensional equation (6) below
T
*
(
h
)
=
T
(
h
)
-
T
avg
T
max
-
T
avg
,
0
≤
T
*
(
h
)
≤
1
wherein
,
(
6
)
T*(h) is the nondimensional outdoor air temperature,
T(h) is the outdoor air temperature at a given time,
T max is the highest temperature during a given day, and
T avg is an arithmetic mean of the highest and the lowest temperatures during the given day, and
(iii) obtaining a temperature prediction function using the equation (7) below
T *( h )=−0.94+0.46 h− 0.25 h 2 +0.04 h 3 −0.003 h 4 +1.07 E− 4 h 5 −1.29 E− 6 h 6 (7)
wherein,
T*(h) is the nondimensional outdoor air temperature and h is a value of an hour hand at the given time of the given day,
(iv) obtaining a monthly average specific humidity using relative humidity and the outdoor air temperature at the given time in reference to the psychrometric chart,
(v) obtaining the linear correlation equation (8) below
f ( d )= C 1 |d− 46|+ C 2 (8)
wherein,
f(d) is a daily specific humidity correlation function,
d is a number of days counted from June 15 to the given day, and
C 1 and C 2 are constants determined by regional characteristics, so that increase and decrease of the daily specific humidity is proportional to a passage of days counted from June 15 to the given day, and
(vi) adding the daily specific linear correlation function □ and an hourly specific humidity of each month to obtain a hourly specific humidity prediction function SH(h,d) represented by equation (9) below
SH ( h,d )=0.011−5.31 E− 4 h+ 2.19 E− 4 h 2 −3.61 E− 6 h 3 +2.52 E− 6 h 4 −7.51 E− 8 h 5 +7.67 E− 10 h 6 −0.000141| d− 46|+0.006375 (9)
wherein,
SH(h,d) is the hourly specific humidity prediction function,
h is the value of an hour hand at the given time of the given day, and
d is the number of days counted from June 15 to the given day;
(vii) obtaining the highest and the lowest temperatures of the next day of the given day from a meteorological office,
(viii) obtaining a hourly prediction temperature T es (h) of next day using the highest and the lowest temperatures and the prediction temperature equation (10) represented below
T es ( h )= T avg +T* ( h )( T max −T avg ) (10)
wherein,
T es (h) is the hourly prediction temperature,
T*(h) is the nondimensional temperature obtained from the equation (6), and
T max and T avg are the highest temperature and an average temperature of next day, respectively,
(ix) obtaining a hourly prediction specific humidity during the next day using the hourly specific humidity prediction function represented by the equation (9), and
(x) providing the hourly prediction temperature T es (h) obtained in the step (viii) to the cooling system for the building as the outdoor air temperature T o and providing the hourly prediction specific humidity obtained in the step (ix) to the cooling system for the building as the specific humidity so that the cooling system for the building can perform the calculation represented by the equation (2).