Document m2oKXqe6m8RZd7E52j7akoqJ

Heating VentiiiATing Air Conditioning Guide 1939 performance of the unit under rated conditions, whereas the contracts ` installing the complete unitary system is normally held responsible f0r the complete performance of the system. Unit equipment justifies its existence due to the following features' 1. Lower cost per unit capacity. Standardized design and volume production mate, possible low cost factory assembly thereby eliminating individual design and handling of every part for each installation. * 2. Flexibility and mobility of equipment. Unitary equipment can be readily located in existing buildings without the necessity of running large ducts through floors and many partitions. Such equipment can. be shifted to meet changing requirements Tenants may obtain the advantages of conditioning when the entire building is not equipped with a conditioning system. In industrial process work, the flexibility of unitary equipment is also advantageous. 3. Lower installation costs. The fact that the equipment arrives on the job in an assembled condition, coupled with the lesser problems of duct work and connecting piping, materially reduces installation costs. s- 4. Small capacities. The small capacities available in unitary equipment have' brought the advantages of controlled air conditions to a number of small offices, stores shops, and individual rooms where specially designed and built central system equips ment would have been uneconomic. SUB-DIVISION OF UNITARY EQUIPMENT For descriptive purposes unitary equipment is sub-divided on a purely functional basis. The following definitions are included in the previously referred to code2. 1. A Heating Unit is a specific air treating combination consisting of means for air circulation and heating within prescribed temperature limits. 2. A Cooling Unit is a specific air treating combination consisting of means for air circulation and cooling within prescribed temperature limits. 3. A Humidifying Unit adds water vapor to and circulates air in a space to be humidified. 4. A Dehumidifying Unit removes water from and circulates air in a space to be dehumidified. 5. An Air Conditioning Unit is a specific air treating combination consisting of means for ventilation, air circulation, air cleaning and heat transfer with control means for maintaining temperature and humidity within prescribed limits. 6. A Cooling Air Conditioning Unit is a specific air treating combination consisting of means for ventilation, air circulation, air cleaning and heat transfer with control means for cooling and maintaining humidity within prescribed limits. 7. A Heating Air Conditioning Unit is a specific air treating combination consisting of means for ventilation, air circulation, air cleaning and heat transfer with control means for heating and maintaining humidity within prescribed limits. 8. A Self-Contained Air Conditioning or Cooling Unit is one in which a condensing unit is combined in the same cabinet with the other functional elements. Self-contained Air Conditioning Units are classified1 according to the method of rejecting condenser heat (water cooled, air cooled, and evaporatively cooled), method of introducing venti lation air (no ventilation, ventilation by drawing air from outside, ventilation by ex hausting room air to the outside, or ventilation by a combination of the last two methods), and method of discharging air to the.room (free delivery or pressure type). 9. A Free Delivery Type Unit takes in air and discharges it directly to the space to be treated without external elements which impose air resistance. *Loc. Cit. Note 1. ^Proposed Standard Method of Rating and Testing Self-Contained Air Conditioning Units for Comfort Cooling prepared by a Joint Committee of the American Society of Refrigerating Engineers, American Society or Heating and Ventilating Engineers. Refrigerating Machinery Association, National Electrical Manufacturers' Association, and Air Conditioning Manufacturers' Association. 432 Chapter 22. Unit Heaters. Ventilators, Air Conditioning. Cooling Units 10 A Pressure Typo Unit is for use with one or more external elements which impose ail resistance. There has grown up in the industry definite branches, in which the neering and application of the equipment vary quite widely. Thus Common acceptance recognizes the following groups of the unitary equip ment defined above. 1 Unit Heaters consisting of an encased heating surface through which air is forced hv means of a fan or blower, located either in or closely adjacent to the heated space, and normally employed only for industrial and commercial applications. 2 Unit Ventilators which are similar in principle to unit heaters but are designed to use outside air with or without provision for recirculation of the air. While unit heaters are largely used for commercial and industrial applications, unit ventilators are intended primarily for school, offices and semi-commercial applications. 3 Cooling Units which are similar to unit heaters except that a cooling medium is used in place of a heating medium and provision is made to collect and remove the con densate. Cooling units are normally applied to the cooling of products for their pre servation or processing (commercial air conditioning) and air conditioning units are used for cooling for comfort. 4. Air Conditioning Units which consist of equipment, to provide control of heating with humidifying or cooling with dehumidifying, coupled with air circulation; all com pactly housed in a single casing. 5. Miscellaneous Unit Equipment and Accessories such as filtering equipment, attic fans, humidifying units and special controls. UNIT HEATERS A unit healer consists of the combination of a heating element and fan or blower having a common enclosure and placed within or adjacent to the space to be heated. Generally no ducts are attached to inlets or outlets, although it is common practice with many unit heaters to equip them with directional outlets or adjustable louvers. While unit heaters are designed primarily to handle all recirculated air, they may be installed to handle either partial or total outdoor air. Compared' with the older method of heating by means of radiation, properly designed and applied unit heaters should: 1. Circulate air in the building at a rapid rate but without objectionable draft. 2. Reduce the temperature differential between the floor and ceiling. 3. Direct the heated air so that uniform temperature distribution be obtained throughout the heated space. 4. Prevent or remove the cold stratum of air commonly found at the floor level. 5. Reduce the number of heating elements required and thereby decrease the cost and extent of the piping, necessary. 6. Maintain a closer control of room temperature either manually or by means of simple thermostats. 7. Produce an economy in heating costs resulting from the sum total of the above advantages. 8. Provide a means of saving floor area or room'space due to.the compactness of the equipment and flexibility of application. TYPES OF UNITS - There are two major types of unit heaters, propeller fan type and centrifugal housed fan type. The housed fan, high velocity (1500 to , 2500 fpm) discharge units with outlets adjustable to deliver air in several directions, are able to project their heating effect over distance of from 433