[TRNSYS-users] problem about type 121b auxiliary heating

[Jay Zhu <zhujiang1124@gmail.com>]

Hey There:
I tried to use unitary air conditioner type 651 (for cooling) and type 121 auxiliary heating  (for heating) to connect with type 56 house controlled by thermostat type 108 , i found a very curious result after testing these types by adding and deleting them 

First time, When i totally delete the type 121, make the system runs, the simulation obvious will show the cooling only.
Second time, when i add the type 121 auxiliary heating, but i set heating point of the thermostat  as low as 5 C, it means the heating will still not running based on the Tampa, Fl weather condition.  So the result will shows the cooling only also without heating.   

it is supposed the plot for these two cases should be exactly same in my opinion. However, cooling consumption of the second case with type 121(but i set it not work at all ) is lower than the first case, and the plot for the room temperature is also different. 

Am i wrong somewhere ? i am so confused for this problem. Thank you in advance 

I changed my simulation to air source heat pump now, but i still wanna know what the exactly problem is for the two simulation cases