Long-Term Performance of Anti-Freeze Protection System of a Solar Thermal System

Round 1

Reviewer 1 Report

I would like to say that paper is very nicely formed, with regards to the scientific, as well as practical aspects.
NewerthIess that, am suggesting a major revision, due to some issues:

-chapter 3.1.: authors should explain why they took a period of the 5 years as a input time series at figure 3. Isn't data from PV Gis more appropriate? Also, figure 3 shows the averaged period from 2004 till 2014; please, also explain this.
-figure 4 should have a legend which color is the consumption, and which outdoor temperature.

-figure 5 should contain basic statistical parameters when regression is done (r and equation of the trend); same story for figure 8.

I think this will approve all statements and conclusions in the paper.

Author Response

I would like to wholeheartedly thank the Reviewer for his time, patience, and efforts to review the paper. It will help me improve it to a better scientific level.

Please see the attachment for more information.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper analyses the performance of a solar collector located in south Poland that uses automatic control system for switching the solar pump as freezing prevention. Before its publications the following comments should be addressed:

 

Major Comments

• Paper only presents experimental data recorded from a solar commercial collector. What is the real contribution to science? What is the novelty of the paper and the merit of being published? There is no modelling neither optimization or comparison among different working strategies. 
• Paper uses 5 years time-span for the analysis. What is the effect of system ageing on its performance? 
• Figure 7 is not sound for many reasons; there is not a clear efficiency definition, very big differences appear among months, efficiency varies significantly for a given month depending on the year, a clear trend cannot be observed. Further discussion and reasoning behind those data is required. Authors suggest that working conditions changed along the years. Therefore, it is not fair comparing different scenarios since it could lead to wrong or biased conclusions. It is suggested finding a different way of expressing the efficiency (normalised?) in order to minimise the contribution of those factors.
• Daily efficiency and daily heat production (among other terms) are not described in the paper. How were those calculated?

 

 

Minor Comments

• No comment is made to pipes tracing (is electric heating or insulating wrapping used to prevent from freezing?)
• It sounds odd in the introduction referring to central tower receiver as tracking collectors, in that application tracking system only applies to the reflectors (heliostats) while the collector is fixed (atop of the tower). Furthermore, linear Fresnel collectors are not generally tracked, as it increases the cost of the technology and parabolic trough would be used instead. That paragraph should also mention the division between concentrating and non-concentrating solar technologies. 
• Line 38 is vague in meaning “each type has its own working principle and its efficiency”. There is not a given efficiency for each technology, there is a standard range of efficiency given typical design (or operation) conditions. It is suggested to replace references 2 to 7 for more general references on the literature
• Lines 54 and 55 are biased; selection of the fluid mainly depends on the application (it means the working temperature)
• Figure 1 could include a scheme of the solar collector as well
• The way of introducing paper [23] in line 101 does not sound scientific.
• Show manufacturer efficiency of the solar collector in Table 1
• Clarify the meaning of negative heating power in Figure 2. Are pumping losses shown anyhow in that graph? It would be also interesting accounting (showing) for pumping power based on switching strategy.
• What are the reasons behind such a big dispersion in monthly solar insolation along the years? What is the TMY-15 information for that location or Meteonorm data?
• English proof-reading is required (grammar tenses, plurals, auxiliary verbs…)

Author Response

I would like to wholeheartedly thank the Reviewer for his time, patience, and efforts to review the paper. It will help me improve it to a better scientific level.

Please see the attachment for more information.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Authors have changed paper due to my comments and suggestions. I am proposing further steps for publishing.

Reviewer 2 Report

Authors addressed reviewer comments appropriately