Features of the operation of air conditioning systems in the summer time

There should be no problems with the operation of properly designed, assembled in accordance with the project and competently serviced air conditioning systems in the summer period, just as there should not be any serious features in their operation.
But it was not for nothing that I immediately made a reservation: “properly designed, installed and maintained”, since all these operations are performed by people who, alas, are prone to make mistakes ...

Design errors, sadly, are quite common. The most common design error is the incorrectly chosen ambient air temperature for calculating refrigeration units (air cooled cooling towers or condensers). Often, designers when selecting equipment take for the calculated maximum temperature specified in the manufacturer's catalog, i.e., +35 ° C. How many customers fell into this trap on peak hot days! In fact, the ambient air temperature around the installed refrigeration equipment on the roof with soft waterproofing in black reaches more than +40 ° , in the shade at outdoor temperature - +35 ° . What happens to refrigeration equipment at such exceeding the estimated conditions? At best, the cooling capacity of each refrigerant circuit will decrease. At the worst - as soon as we reach the pressure limit of the built-in protection, the compressors of the refrigeration circuits will start shutting down and the whole system will stop until the pressure in it decreases. Moreover, it is impossible to predict in advance or accurately calculate at what ambient air temperature the value of the emergency pressure in the compressor will be exceeded.

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 in the calculations to overestimate the ambient air temperature. As a result, the system usually turns out to be somewhat “oversized”, but more resistant to high peak temperatures.

To avoid serious mistakes in the project, in my opinion, a good practice is its audit, carried out 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.
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But if the system is already built on the basis of a “lowered” working temperature, there are two ways to maintain the cooling capacity:
1. The easiest way is to put the backup refrigeration unit into operation: in this way we will be able to somewhat compensate for the decrease in cooling capacity. But in this case we have two serious limitations: firstly, the presence of sufficient electrical power to start the backup chiller, and secondly, this option will work only when the ambient temperature does not cause the upper limit pressure values ​​of the compressors to be exceeded.

2. The most accessible method is artificial adiabatic lowering of the ambient air temperature. Simply need to organize watering of the cooling towers or condensers with water. It is the properly organized service of adiabatic cooling of the outside air entering the refrigeration equipment that can save the situation with the cooling capacity during peak hot hours, and during the rest of the summer time - significantly reduce the rate of electricity consumption by compressors.

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

The answer to the first question is with a liquid that does not impair the efficiency of the units. Often, watering at peak temperatures is made with ordinary tap water, as a result of which insoluble calcium salts of aluminum lamellae and copper tubules are gradually coated with insoluble calcium salts. Under the action of these salts, the lamellae simply begin to break down and crumble, and a crust of calcium carbonate forms on the tubes. Accordingly, the heat exchanger ceases to be properly purged with air, plus the area of ​​heat exchange 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 needs to be made with prepared water that does not contain calcium ions, even when using irrigation only in situations where the temperature exceeds the calculated one.

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

Now about the installation ...

Involvement of an experienced installation organization in assembly work is practically a guarantee of high-quality assembly, but for complete confidence it is necessary to conduct operational control of assembly work (technical supervision with maintaining a work log) and control of compliance of the system to the project, displaying all the shortcomings and changes made in the author's supervision and as-built documentation.

There is still a very important point before installation: this is the choice of the manufacturer and supplier of equipment. Very often at this stage, in order to save money, they replace the equipment specified in the project with a similar, but cheaper, other manufacturer. Here lies the danger! To reduce the price, suppliers very often unfairly, or, in the absence of sufficient time to work out a solution, only the catalog data compares the equipment. As a result, equipment is selected that meets the requirements of the project only in certain modes, and the stability reserve that was laid during the design process is coming to naught. As a result, the system needs to be refined and the power consumption of the entire cooling system is too high from the design.
Our recommendation: in the struggle to save 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 carefully examine the compliance of technical indicators with design requirements.

Now about the operation ...

According to the Russian proverb, sledges need to be prepared in the summer, and a cart - in the winter, for cold supply systems, winter and summer are not exactly the right time to prepare for another season ...

Our "cart" is better to prepare in the spring, and the "sleigh" - in the fall.

Summer and winter is the time of constant monitoring and testing of design decisions, as well as experiments and training for 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 experiments on efficiency. During the cold period of the year, it is impossible to carry out full maintenance on street air-cooled units (chillers, condensers or cooling towers) because it is impossible to diagnose the systems operating pressures. The only suitable time is spring with a street temperature above +5 ° C.

We should not forget about the previously mentioned water treatment system used for the irrigation of condensers or cooling towers. If the station has not been operated during the cold season, it is necessary to work on its re-entry and start-up.
Proper planning and organization of maintenance is the key to trouble-free work in general and a quiet life in summer, with peak loads on the system.

With 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 comes from a single server room of 550 kW, organized on freon cabinet air conditioners with remote air-cooled condensers. Long chose the location of street capacitors. They chose the darkest place - the north side of the facade. For a long time they chose an indent from the fence and the outer wall of the facade. Finally reached a consensus, by that time it was December. In March, the installation began, and by the end of the summer, the data center had already started working under a minimum load. In general, May - and abundantly blossoming and growing, after a meter planted along the northern facade of the poplar, were not noticed and taken into account by anyone. However, the next year, by the 20th of May, we received an emergency server shutdown. Well, the customer didn’t expect his 16 capacitors to gently “vacuum” the entire sidewalk from poplar fluff ... It seemed obvious to buy a high-pressure washing station or hire a service organization with a certain time of arrival, but the customer pulled the net around everyone 16 capacitors, and after three days the surface area of ​​the collector increased more than three times the original. True, now they could be cleaned without the use of special means ... Pooh 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 that must arrive and remove poplar fluff from outdoor heat exchange equipment within a specified time. Or these works should be able to perform service operation.

One more feature in service of freon central airs with portable condensers. Such units must be equipped with sets of low-temperature start of the compressor. Paradoxically, the correct calculation of the winter low-temperature start-up system affects the stability of the system in summer.

As it is known, the compressor circuit can safely operate at ambient temperatures below -60 ° C, only lubrication in the condenser fans can serve as a limitation. The low-temperature kit is needed to start the cooled refrigeration compressor circuit when the freon in the condenser and pipes outside starts to compress when cooled and the pressure in the whole circuit drops below the compressor’s alarm value.

The standard precision conditioner of direct evaporation (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 enlarged built-in receivers. Such a compromise leads to the fact that every fall in such air conditioners it is necessary to refuel the freon to the maximum, and in the spring period to bleed it (at best, to collect the regeneration station) in the ozone layer of the atmosphere. If it is not set off, the compressor will stop due to the high-pressure sensor triggering. Manufacturers of precision air conditioners or engineering services with years of experience and high-class engineers recommend individually counting all low-temperature kits, depending on many factors. Freon systems with such correctly selected low-temperature kits do not require any additional actions in the summer season.

A working draft by professionals and its installation with commissioning is the key to the perfect operation of the air-conditioning system at its peak period of the year, that is, in the summer.

Author: Vladimir Levin, TsODY.RF Magazine No. 3