Features of the operation of air conditioning systems in the summer

There should be no problems with the operation of correctly designed, installed in accordance with the project and competently maintained air conditioning systems in the summer, just as there should not be any serious features in their operation.
But it was not in vain that I immediately made a reservation: “correctly designed, installed and maintained,” since all these operations are performed by people who, alas, tend to make mistakes ...

Design errors, sadly enough, are quite common. The most common design error is the incorrect ambient temperature for the calculation of refrigeration units (air-cooled cooling towers or condensers). When choosing equipment, designers often take the calculated maximum temperature indicated in the manufacturer’s catalog, i.e. +35 ° C. How many customers came to this trap during the peak hot days! In fact, the ambient temperature around the installed refrigeration equipment on the roof with soft black waterproofing reaches over +40 ° C, in the shade at street temperature - +35 ° C. What happens to refrigeration equipment with such excesses of design conditions? In the best case, the cooling capacity of each refrigeration circuit will decrease. In the worst case, as soon as we reach the limit value of the built-in protection pressure, the compressors of the refrigeration circuits will turn off and the entire system will stop until the pressure in it decreases. Moreover, it is impossible to predict in advance or accurately calculate at what temperature the ambient air will exceed the value of the emergency pressure in the compressor.

In order to avoid this error, it is necessary to ask the manufacturer for technical data on the behavior of their equipment at elevated temperatures, and when calculating, increase the ambient temperature. As a result, the system usually turns out to be somewhat “oversized”, but more resistant to high peak temperatures.

In order to avoid serious mistakes in the project, in my opinion, it is good practice to audit it by independent experts, as well as certification for compliance with one or another standard (Uptime Institute, BICSI, TUV, etc.), which focuses on ensuring given readiness systems in any, including critical, operating conditions.

But if the system has already been built based on the calculation of the "lowered" operating temperature, there are two ways to maintain refrigeration capacity:
1. The easiest way is to put the backup refrigeration unit into operation: this way we can somewhat compensate for the decrease in refrigeration capacity. But in this case, we have two serious limitations: firstly, the availability of sufficient electric power to start the backup refrigeration machine, and secondly, this option will work only if the ambient temperature does not exceed the upper pressure limits of the compressors.

2. The most affordable way is to artificially adiabatically lower the ambient temperature. It is simply necessary to organize watering of cooling towers or condensers with water. It is precisely the adiabatic cooling of the outdoor air that enters the refrigeration equipment that is properly organized by the maintenance service that can save the situation with refrigeration power during peak hot hours, and in the rest of the summer, significantly reduce the energy consumption of compressors.

Let's look at the concept of “properly organized adiabatic cooling”. There are two questions: what and how?

The answer to the first question is a liquid that does not impair the performance of the units. Often, irrigation at peak temperatures is carried out with ordinary tap water, as a result of which aluminum lamellas and copper tubes are gradually coated with insoluble calcium salts. Under the influence of these salts, the lamellas begin to simply collapse and crumble, and a calcium carbonate crust forms on the tubes. Accordingly, the heat exchanger ceases to be normally purged with air, plus the heat exchange area is sharply reduced. After three years, all this leads to a decrease in the capacity of refrigeration equipment to an almost unacceptable level, and there is a need to replace heat exchangers. So, irrigation must be done with prepared water that does not contain calcium ions, even when using irrigation only in situations if the temperature exceeds the calculated one.

The answer to the second question is refinement, namely the creation of a complete irrigation system for heat exchangers. The creation of such a system will not only allow trouble-free temperature peaks to pass, but also significantly reduce power consumption during normal operation.

Now about the installation ...

Attracting an experienced installation organization to the installation work is almost a guarantee of high-quality installation, however, for complete confidence it is necessary to conduct operational control of installation works (technical supervision with a log of work) and control of the compliance of the completed system with the project, showing all the shortcomings and changes in the journal of architectural supervision and executive documentation.

There is still a very important point before installation: this is the choice of the manufacturer and supplier of the equipment. Very often at this stage, in order to save financial resources, replace the equipment specified in the project with a similar, but cheaper, other manufacturer. This is where the danger lies! To reduce the price, suppliers very often in bad faith or, in the absence of sufficient time to develop a solution, only on the basis of catalog data compare equipment. As a result, equipment is selected that only, under certain conditions, meets the requirements of the project, and the stability margin that was laid down during the design comes to naught. As a result, the system refinement is again required and the power consumption of the entire cooling system is inflated from the design power consumption.
Our recommendation: in the fight for saving money, you need to rely on common sense, engineering culture, and without fail, try to see with your own eyes the equipment that you intend to install, as well as more carefully and thoroughly examine the conformity of technical indicators with design requirements.

Now about the operation ...

In accordance with the Russian proverb, sledges need to be prepared in the summer, and the cart in the winter, for winter and summer cooling systems are not quite the right time to prepare for another season ... It is

better to prepare our "cart" in the spring, and the "sleigh" in the fall.

Summer and winter is a time of tireless monitoring and verifying the operability of design decisions, as well as experiments and training on actions in critical situations and during peak loads.

It is in the summer periods that one can see the effectiveness of the modernization carried out, which means that it is necessary to conduct efficiency experiments. In the cold season, it is impossible to carry out full-fledged maintenance on outdoor air-cooled units (chillers, condensers or cooling towers) due to the impossibility of diagnostics at the operating pressures of the systems. The only suitable time is spring with street temperatures above +5 ° C.

We must not forget about the previously mentioned water treatment system used to irrigate condensers or cooling towers. If the station was not operated during the cold season, it is necessary to carry out work on its decommissioning and putting it into operation.
Proper planning and organization of maintenance is the key to trouble-free operation in general and a quiet life in the summer, with peak loads on the system.

Having a detailed schedule of scheduled maintenance for each device, you can quickly prepare the entire refrigeration system for operation in the summer.

An interesting story is recalled from a server room at 550 kW, organized on freon cabinet air conditioners with remote air-cooled condensers. Long chose the location of street capacitors. We chose the darkest place - the north side of the facade. For a long time they chose the indent from the fence and the outer wall of the facade. They finally reached a consensus, by which time it was December. Installation began in March, and by the end of summer, the data center had already started under minimal load. In general, May - both abundantly blooming and growing, a meter later planted along the northern facade of the poplar, was not noticed and taken into account by anyone. However, the very next year, by the 20th of May, we received a server emergency stop. Well, the customer didn’t expect it, that its 16 condensers gently “vacuumed” the entire sidewalk from poplar fluff ... It seemed obvious - to purchase a high-pressure washing station for your operation service or to hire a service organization with a certain arrival time, but no: the customer pulled a mesh around all 16 capacitors, and three days later the surface area of ​​the down box has increased more than three times from the original. True, now they could be cleaned without the use of special equipment ... Fluff from poplars, willows, dandelions is a temporary phenomenon, but the operation service should have clear instructions on how to act at this time. and after three days, the surface area of ​​the downbox increased more than three times from the original. True, now they could be cleaned without the use of special equipment ... Fluff from poplars, willows, dandelions is a temporary phenomenon, but the operation service should have clear instructions on how to act at this time. and after three days, the surface area of ​​the downbox increased more than three times from the original. True, now they could be cleaned without the use of special equipment ... Fluff from poplars, willows, dandelions is a temporary phenomenon, but the operation service should have clear instructions on how to act at this time.

During the flowering of poplars, it is necessary to have a mobile outsourcing team, which within a specified time should come and remove poplar fluff from the outdoor heat exchange equipment. Or these operations should be able to perform the service operation.

Another feature in the maintenance of freon air conditioning systems with remote condensers. Such units must be equipped with compressor low temperature start kits. Paradoxically, the correct calculation of the winter low-temperature start-up system affects the stability of the system in the summer.

As you know, the compressor circuit can easily operate at outdoor temperatures below -60 ° C, only lubrication in the condenser fans can serve as a limitation. A low-temperature kit is needed to start a cooled refrigeration compressor circuit, when the freon located in the condenser and pipes on the street starts to compress during cooling, and the pressure in the entire circuit drops below the compressor alarm value.

The regular precision direct evaporation air conditioner (freon) is equipped with a freon receiver. Its volume is not enough to compensate for the decrease in pressure. Some manufacturers complete the so-called low-temperature kits with larger integrated receivers. Such a compromise leads to the fact that every fall in such air conditioners it is necessary to refuel freon to the maximum, and in the spring to bleed it (at best, collected by a regeneration station) into the ozone layer of the atmosphere. If it is not vented, the compressor will stop due to the operation of the high pressure sensor. Manufacturers of precision air conditioners or engineering services with many years of experience and high-class engineers recommend individually calculating all low-temperature kits depending on many factors.

A working project completed by professionals and its installation with commissioning is the key to the flawless operation of the air conditioning system in its peak season, that is, in the summer.

Author: Vladimir Lyovin, TsODy.RF Journal No. 3