It's telling you that the design parameters do not conform with psychrometrics. Usually, design values for water-side and air-side are 5.5C and 11.1C, respectively. Your air-side delta T does not provide this value. Now you can operate at a supply air temperature of 18C if you like, but you should "size" the coil differently. As the message states, I would change the sizing information accordingly. I have tried this and it still leads to the same error, hopefully this won't happen to you. So I am not exactly sure if the error will disappear without some iteration.
If you do want to size your coil for an exiting air temperature of 18C at this air flow, entering air condition, and water temp/flow rate, then you will have to manually size the coil to get there.
The amount of reheat you use will depend on the supply air temperature (your 18C) and flow rate vs the zone loads. You can also reset the supply air temperature based on outdoor temperature (SetpointManager:OutdoorAirReset) to help reduce the amount of reheat.
On 7/29/2011 10:38 AM, Jean marais wrote:
I have the following error:
************* Beginning System Sizing Calculations
************* Beginning Plant Sizing Calculations
** Warning ** In calculating the design coil UA for Coil:Cooling:Water DOAS COOLING COIL
** ~~~ ** the apparatus dew-point is below the coil design inlet water temperature;
** ~~~ ** the coil bypass factor is unrealistically large;
** ~~~ ** the coil outlet design conditions will be changed to correct the problem.
** ~~~ ** The initial design conditions are: Tair,in = 24.4500
** ~~~ ** Wair,in = 9.478796E-003
** ~~~ ** Twater,in = 6.0000
** ~~~ ** Tair,out = 18.0000
** ~~~ ** Wair,out = 8.000000E-003
** ~~~ ** The revised design conditions are: Tair,out = 14.5987
** ~~~ ** Wair,out = 9.371939E-003
All my coil inputs possible are autosized. Zone and System humidity designs are 0.008 (default). My outlet Tair design is 18 deg (as seen in the error msg.)
1) What is going on here exactly?
2) How can I enter other parameters so that the error does not occur and no reheat is nessesary.
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