3. Drill the pronunciation of the words suggested above

4. Translate the following noun-groups into Russian:

All air central air-conditioning systems, space thermostat, air-water central air-conditioning systems, conditioned systems, space loads, supply air temperature, a cooled air stream, load conditions, constant tem­perature, conditioned air, fixed minimum ventilation rates, hybrid systems, system efficiency.

5. Answer the questions using the given words in brackets:

1. What groups of central air-conditioning systems exist?

(constant volume, variable temperature system, variable volume, constant temperature system)

2. What does the constant volume variable temperature system supply?

(a constant amount of conditioned air at proper temperatures)

3. What does the variable volume, constant temperature systems supply?

(a varying amount of constant temperature conditioned air)

6. Reader the following English sentences into Russian:

1. Generally, these systems are very simple to design and reliable to operate.

2. Energy is washed under partial load conditions because of mixing or reheat.

3. Space temperature control is not dependant on mixing or reheat.

4. However, only cooling can be provided.

5. A group of hybrid systems evolved from these two basic groups. ?

7. Read the text "Central Air-conditioning Systems" and

• mark the paragraphs characterizing central air-conditioning systems;

• say if the same groups of systems exist in Russian;

• find the information on the difference between constant volume, variable temperature systems and variable volume temperature systems;

• define if these two systems are the only ones used and what the text says about it;

• analyzing the text from the point of view of the future engineer, express your attitude towards the problems discussed in the article, say if everything could be accepted without doubts. And if you had the opportunity of talking to its author of the article what would you clear up?

Central air-conditioning systems

All air or air-water central air-conditioning systems can be catego­rized into two basic groups as follows:

1. Constant volume, variable temperature systems.

2. Variable volume, constant temperature systems.

Constant volume, variable temperature systems supply a constant amount of conditioned air at proper temperatures in response to each thermostat to meet prevailing space loads. Supply air temperature is controlled by:

1. mixing a cooled air stream with a heated or bypassed air system;

2. reheating a cooled air stream.

Generally, these systems are very simple to design and reliable to operate. Although any space served by the system can be heated or cooled, energy is wasted under partial load conditions because of mixing or reheat.

Variable volume, constant temperature systems respond to each space thermostat by supplying a varying amount of constant temperature conditioned air to meet the prevailing space load. Since this type is rela­tively new, some adjustment in design philosophy is necessary in the minds of engineers who are used to constant volume system design.

Space temperature control is not dependent on mixing or reheat thereby. Eliminating energy washed, however, only cooling can be pro­vided. Heating is generally supplied by some form of supplementary sys­tem. These systems also have limitations for buildings where fixed mini­mum ventilation rates are required.

Recognizing that both constant volume and variable volume systems have good features and limitations, a group of hybrid systems evolved from these two basic groups to optimize system efficiency, cost and con­venience.