Topics: Thermodynamics, HVAC, Heat Pages: 5 (1610 words) Published: June 11, 2013
In the modern days energy has the significant role in our life. With development where we got comfortable life and much modern facilities where we got some problem with excessive use of energy resources as declining of energy sources, climate change. So it is an big challenge for present and future generations as the cost of energy increase and its supply decrease, older buildings needs to modified and new buildings designed to use less energy. The optimization of heating, ventilation and air conditioning system in term of energy efficiency is part of this assignment as how wisely to manage and use the energy recourses in our daily life and how the technology can help us in minimize the energy use in building sector particularly in HVAC field,

In energy consumption Australia is the world’s eighteenth largest energy consumer and ranks fourteenth on per person basis. Building sector is responsible for 19% of total energy consumptions of the country and 23% green house emission (residential 13% commercial 10% ) residential and commercial buildings use the energy for different purposes. Nearly 65% of residential energy consumption use is for heating and cooling. 70% of energy consumption are estimated to contribute to HVAC systems in building sector. Running cost of all building appliances and systems depends upon the following factors as size of unit, time, load and electricity rate an example of the running cost If the data sheet has Power Input figure in kW (not the heating or cooling capacity of the unit) you simply multiply this number by your local energy cost in kWh (kilowatt hours) to give you a running cost in cents. If the input power figure is not given you will need to divide the Cooling Capacity figure by the EER (energy efficient rating) figure and then multiply this by your local energy cost. EER can vary for each machine according to its design and technology For example Input power rating for a 6.0kW of a wall hung split system Electricity local rate is 25 cent per KW

Cooling capacity of unit has 3.26 EER
Cooling Capacity is 6.0 divided by EER of 3.26 = 1.84
e.g.2 Running cost = 1.84 X 25 = 46 cents per hour
For heating use the heating capacity and the COP figures instead of cooling capacity and EER. For this unit the Heating capacity is 7.0 and the COP is 3.41 7.0 divided by 3.41= 2.05 multiply this by your energy cost (25c*) and you get a heating mode running cost of 51.25 cents per hour.

The capacity of hvac systems is degined in the maximum operation conditions. Most important factors are solar load, occupancy ambient temperature equipment and lighting load etc if the design capacity is greater than the actual load the system will become unstable and oveheat or over cool and effwct the consumption and running cost Cycling control is most effective way to meet the part load conditions as conditioning space needs less enery as the system designed to deliver the system will run for particular time and turn off and start the lod increase the system will run for longer timeand off period will be shorter * It is desirable to avoid the use of single large compressor where the refrigeration load is variable. Multiple smaller machines, with working machines operating close to full load is more desirable.

The economizer is part of the control system that senses this condition, opens the OA damper and closes the RA damper, using the cooler OA instead of mechanical cooling to condition the space.  In order to have a better temperature control, low limit thermostat modulates outside air, return air and exhaust air dampers to keep the desired mixed air temperature. Moreover, other controls, such as outside air high limit or morning warm up low limit, can be added to make a more efficient system. Temperature economizers are controlled by temperature; sensors read...
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