Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Estimation of Evaporator Valve Sizes in Supermarket Refrigeration
  Cabinets   In many applications, e.g. fault diagnostics and optimized control of
supermarket refrigeration systems, it is important to determine the heat demand
of the cabinets. This can easily be achieved by measuring the mass flow through
each cabinet, however, that is expensive and not feasible in large-scale
deployments. Therefore it is important to be able to estimate the valve sizes
from the monitoring data, which is typically measured. The valve size is
measured by an area, which can be used to calculate mass flow through the valve
-- this estimated value is referred to as the valve constant. A novel method
for estimating the cabinet evaporator valve constants is proposed in the
present paper. It is demonstrated using monitoring data from a refrigeration
system in a supermarket consisting of data sampled at a one-minute sampling
rate, however it is shown that a sampling time of around 10-20 minutes is
adequate for the method. Through thermodynamic analysis of a two-stage CO2
refrigeration system, a linear regression model for estimating valve constants
was developed using time series data. The linear regression requires that
transient dynamics are not present in the data, which depends on multiple
factors e.g. the sampling time. If dynamics are not modeled it can be detected
by a significant auto-correlation of the residuals. In order to include the
dynamics in the model, an Auto-Regressive Moving Average model with eXogenous
variables (ARMAX) was applied, and it is shown how it effectively eliminates
the auto-correlation and provides more unbiased estimates, as well as improved
the accuracy estimates. Furthermore, it is shown that the sample time has a
huge impact on the valve estimates. Thus, a method for selecting the optimal
sampling time is introduced. It works individually for each of the evaporators,
by exploring their respective frequency spectrum.

21
The categories of this paper are: adap-org
18
The categories of this paper are: econ
23
The categories of this paper are: solv-int
30
The categories of this paper are: q-alg
25
The categories of this paper are: patt-sol
9
The categories of this paper are: nlin
0
The categories of this paper are: hep-ph
15
The categories of this paper are: nucl-ex
20
The categories of this paper are: acc-phys
28
The categories of this paper are: alg-geom
22
The categories of this paper are: chao-dyn
29
The categories of this paper are: funct-an
2
The categories of this paper are: math
33
The categories of this paper are: plasm-ph
8
The categories of this paper are: hep-ex
36
The categories of this paper are: cmp-lg