1.Approximately how many hours per year you will be operating the unit 2.How much a kilowatt-hour (kWh) costs in your area Let's say that you plan to use the air conditioner in the summer (four months a year) and it will be operating about six hours a day. Let's also  imagine  that  the  cost  in your area  is $0.10/kWh. The difference in energy consumption between the two units is 200 watts, which means that every five hours the less expensive unit will consume 1 additional kWh (and therefore $0.10 more) than the more expensive unit. Assuming that there are 30 days in a month, you find that during the summer you are operating the air conditioner: Since the more expensive unit costs $100 more that means that it will take about seven years for the more expensive unit to break even. See this page for a great explanation of seasonal energy efficiency rating (SEER). Split-system Units A split-system air conditioner splits the hot side from the cold side of the system。 The  cold  side,  consisting  of  the  expansion  valve  and  the  cold  coil,  is  generally  placed  into  a furnace or some other air handler. The air handler blows air through ducts. The hot side known as the condensing unit, lives outside the building. The unit consists of a long, spiral coil shaped like a cylinder.  Inside  the  coil  is  a  fan,  to  blow  air  through  the  coil,  along  with  a  weather-resistant compressor  and  some  control  logic.  This  approach  has  evolved  over  the  years  because  it  is low-cost, and also because it normally results in reduced noise inside the house (at the expense of increased noise outside the house). Besides the fact that the hot and cold sides are split apart and the capacity is higher (making  the coils and compressor  larger), there is no difference between a split-system and a window air conditioner. In warehouses, businesses, malls, large department stores, etc., the condensing unit normally lives on the roof and can be quite massive. Alternatively, there may be many smaller units on the roof, each attached inside to a small air handler that cools a specific zone in the building. Let's take a look now at a chilled-water air conditioner. Chilled-water System In  larger buildings  and  particularly  in multi-story buildings,  the  split-system  approach begins  to run  into  problems.  Either  running  the  pipe  between  the  condenser  and  the  air  handler  exceeds distance limitations (runs that are too long start to cause lubrication difficulties in the compressor), or the amount of duct -work and the length of ducts become unmanageable. At this point, it is time to think about a chilled-water system. In  a  chilled-water  system,  the  entire  air  conditioner  lives  on  the  roof  or  behind  the  building.  It cools water to between 40 and 45 F (4.4 and 7.2 C). This chilled water is  then piped  throughout the building and connected to air handlers as needed. There is no practical limit to the length of a chilled-water pipe if the system can be got well - insulated. Whenever you walk behind a building and  find a unit  that has  large quantities of water  running through a plastic mesh, you will know you have found a cooling tower! In many office complexes and college campuses, cooling  towers and air conditioning equipment are  centralized,  and  chilled water  is  routed  to  all of  the buildings  through miles of underground pipes. Based  on  dynamic  load  track  central  air-conditioning  system  entire  closed  loop  energy conservation technology research. 1. introductions The energy conservation may say is the building character automatic control system starting point and  the  home  to  return  to.  It  is  well  known,  in  the  intelligent  construction,  HVAC  (heating, ventilates and air conditioning) the system consumes to have to occupy the building consumption total energy  enormous partial proportions, approximately about 50% ~60%. Specially cold: East the  unit,  the  cooling  tower,  the  circulating  water  pump  and  the  air  conditioning  unit,  the  new atmosphere  unit,  all  are  consumes  energy  the  big  household.  Therefore  really  has  essential develops one effective air-conditioning system energy conservation method, especially uses  is  in improves  in  the  existing  building  air-conditioning  system  automation  the  aspect.  DDC (Directdigitalcontr01) the direct of numerical control, is a structure simple operation easy control device, it may borrow by the connection switches over the equipment to make the systems control along  with  the  load  change,  like  the  air  conditioning  cold  water  circulatory  system,  the  air conditioning  box  frequency  conversion  automatic  amount  of  wind  adjustment  and  the  cooling tower  radiation  ventilator  frequency  conversion  holds  controls  and  so  on,  may  let  an air-conditioning system more effective revolution, like this, not only brings the very big economic efficiency for the estate management, moreover also may cause the system to move under a better operating mode, thus lengthens the equipment the service life as well as achieved provides goal of the comfortable air conditioning environment and the energy conservation. The  general  building  commonly  used  air-conditioning  system  has CAV, VAV, VWV  and  so  on, respectively has differently holds controls the way, all may use DDC to control. 1 decides the amount of wind system (ConstantAirVolume, is called CAV). Decides  certainly  the  amount  of wind  system  the  amount  of wind which  blows  out  for  the  air conditioner certainly, provides coldly  (is warm)  the gas which  the air conditioning  region needs. When air conditioning region load variation, then changes the blast temperature to deal with in the room  to  shoulder,  and  achieves  the  maintenance  indoor  temperature  to  the  comfortable  area request.  空调节能技术英文文献和中文翻译(2):http://www.youerw.com/fanyi/lunwen_31576.html