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Safwan, It is always a VERY good idea to do an energy balance and if it is balancing to within 1kWh over a month then I think you can have great confidence that your model is correct (of course that doesn't necessarily mean that the model reflects reality but it is a good first step). 2- I found there was no way to calculate cooling load while running the simulation, so I calculated it separately. any idea? this question gets to the heart of how TRNSYS is different from a lot of other building modeling tools. Many tools calculate a space load and then try to meet that load with the HVAC system model. It is difficult in this case to write an energy balance because you have to make the assumption that the HVAC system can deliver exactly the amount of energy required by the load at all times. While TRNSYS can operate in that manner, you can also use it to get a lot closer to the way that a building actually operates. To do so you turn off the automatic heating and cooling in TRNBuild and allow the building temperature to float. Then you implement a thermostat model and decrease the simulation time step to something on the order of 1 minute. You then implement your HVAC system and control it (determine whether fans, pumps, and equipment) should be ON or OFF based on your thermostat's output. The HVAC system outputs (air flow rate, temperature, and RH) are inputs to VENTILATION types defined in TRNBuild. You can then do your energy balance using the actual amount of energy that was transferred by the equipment to the zone. 3-When I come to (pipes, duct and fan loss) some of cold pipe will gain heat instead of lost it, so should I add it to heat losses or subtract it? you just need to be consistent about the sign of the terms in your energy balance. In a water loop you might define energy into the loop as positive (an energy gain) and energy out of the loop as negative (an energy loss). If the liquid in a pipe is hotter than the ambient then it will lose energy to the ambient and you take that term to have a negative sign in your balance. If the liquid is colder than ambient then it will gain energy from its surroundings and you would take that as a term with a positive sign. regards, David On 09/21/2015 08:48, Safwan Kanan
wrote:
-- *************************** David BRADLEY Principal Thermal Energy Systems Specialists, LLC 22 North Carroll Street - suite 370 Madison, WI 53703 USA P:+1.608.274.2577 F:+1.608.278.1475 d.bradley@tess-inc.com http://www.tess-inc.com http://www.trnsys.com |