RE: [EnergyPlus_Support] Time heating setpoint not met

Setting the zone thermostat value to a different value to observe the result is a very powerful degugging tool.

"if i set heating setpoint =25C then i see in the winter design day the zone mean air temperaure is nearly 24-25C . "

In this case, the highest temperaute is the same as the set point. The system is controlling the temperature. For the 24°C period, the system is under capacity. If the sizing was doen with people, lighting , and equipment, removing these would need more heating.

"if i set heating setpoint =30C then i see in the winter design day the zone mean air temperaure is nearly 24-25C".

In this case, the system under capacity, and the thermosat is not controlling the temperature.

If the desired Winter temperature is 15-20°C, the system capacity can be reduced some more.

The above two cases assume that the heating setpoint is for the zone thermostat.

However, if the value is for the HW heater outlet feeding the radiator, the 25°C set point will have lower zone emperatures as given below, nearly 20-21-19°C.

This is because the exit temperature of a radiator is always below the inlet temperature of 25°C. When the water is not following, a radiator will transfer heat slowly to or from the zone by conduction and convection, until the temperature is the same.

When you run the sizing simulation, the flowrate for the radiator is adjusted to the worse case of that day or period for that zone only. In your case, the solar radiation is also turned off. Therefore, the flow rate obtained is only good for that outdoor and indoor condition

The zone temperature is expected not to me the setpoint temperature of the zone, for all hours of a day.

Dr. Li

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: t.t111ir@xxxxxxxxx
Date: Sat, 3 Mar 2012 12:00:38 +0000
Subject: Re: [EnergyPlus_Support] Time heating setpoint not met

i wrote wrong in the yellow highlighted line , the red line in correct

From: Tooran <t.t111ir@xxxxxxxxx>
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Sent: Saturday, March 3, 2012 3:26 PM
Subject: [EnergyPlus_Support] Time heating setpoint not met

dear members ,

i want to design the hot water plant loop and i wnat to know what size pump and boiler must have to that their capacity is engough for keeping the zone mean air temperature = 25 C ( i set heating setpoint =25C) for winter design day , but when i run it i see in the winter design day i have time heating setpoint not met and the zone mean air temperature is nearly 20-21-19 C.
if i set heating setpoint =25C then i see in the winter design day the zone mean air temperaure is nearly 24-25C .
if i set heating setpoint =30C then i see in the winter design day the zone mean air temperaure is nearly 24-25C .
could you help me and describe it why this happens?
thanks

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