Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
This a rather large question, and it's going to be hard to really explain in detail how the different sizing routines work and play together. That's why the Engineering Reference has such a huge section treating about sizing.
I'll do my best to get to the point and you'll have to forgive any gross simplification.
The first of such simplifications, is that I'll take out the WaterHeater:Mixed from the problem, I'm assuming it doesn't have a built in heater and is just served by the PlantComponent:TemperatureSource[1]
For the sizing, it's done on the design days indeed.
It's going to size stuff in this order (that's what I understand at least): Zone, System (airloop), Component, and Plant. Important: please read more in the Sizing Manager section of the engineering reference.
(FYI, it's also going to start by looking at the global Sizing:Parameters)
First, it's going to size your zones, based on the Sizing:Zone (I/O) object, in which you enter the supply air temperature, humidity ratio, and potentially air flow rate (or tell it to calculate the air flow rate based on design days). That'll give you the heating and cooling loads.
You have no airloop here, so System is skipped.
Second, it's going to look at your components, in your case the ZoneHVAC:Baseboard:Convective:Water, and try to size the heating coil. The relevant section of the engineering reference is Coil:Heating:Water Sizing > Zone Coils
Get input from Zone Sizing
First, it gets a few input stored in the Zone Sizing routine in Zone Design Data Array (read for variable definition)
It gets the zone heating coil design air inlet temperature [C]:
$$T_{in,air} = DesHeatCoilInTemp_{zone}$$
This is calculated by checking the zone temp at sizing (from the Tstat), and the potentially Outside Air Fraction and temperature (at the design day).
And the zone design heating supply air temperature [C]:
$$T_{out,air} = HeatDesTemp_{zone}$$
This is directly entered in Sizing:Zone.
The zone heating coil design air inlet humidity ratio [kg/kg] will be used later for $cp,air$
$$W_{out,air} = HeatDesHumRat_{zone}$$
This is directly entered in Sizing:Zone.
Then the the zone design heating air mass flow rate in [kg/s]
\begin{equation} \dot mair,des = DesHeatMassFlow_{zone} \end{equation}
This is calculated from in the Zone Sizing, based on what's provided for air flow rate (can be a number, or "DesignDay" or "DesignDayWithLimit")
Size the coil
It then calculates the coil capacity:
\begin{equation} Qcoil,des = cp,air\dot mair,des\cdot (Tout,air - Tin,air) \end{equation}
Here $cp,air$ is calculated at the outlet humidity and the average of the inlet and outlet temperatures.
With the coil load and the user specified (in a Sizing:Plant object - important!) design hot water temperature decrease, calculate the max water flow rate:
\begin{equation} \dot Vcoil,water,max = Qcoil,des/(Cp,water\cdot \rho water\cdot \Delta Tplt,hw,des) \end{equation}
Documentation:
The design plant loop flow rates are set by the sum of the needs of the demanding components on each loop. For hot water loops that's the hot water coils.
What you need to really remember: to size your hot water coil, the program actually gets user inputs defined in several objects and uses several sizing routines. It will use the design temperatures (and air flow rates in some cases) defined in the Sizing:Zone object and the resulting calculated laods, as well as the plant delta T you specify in Sizing:Plant.
It's up to you to determine whether you do need to feed information for the sizing routines to work properly.
My two cents is that if in your application the zone design temps aren't changing, and if you intend to keep the same constant delta T in the plant loop, you shouldn't need to feed new info for co-simulation.
If you do need to change it for the sizing routines, I'm sure there's a way (post a new question though).
[1]You can read on how to autosize its built-in heater capacity using a WaterHeater:Sizing, which you'll want to set to Peak Draw given your specific application and carefully chose the indirect recovery time to determine the heater capacity needed.
| | 2 | No.2 Revision |
This a rather large question, and it's going to be hard to really explain in detail how the different sizing routines work and play together. That's why the Engineering Reference has such a huge section treating about sizing.
I'll do my best to get to the point and you'll have to forgive any gross simplification.
The first of such simplifications, is that I'll take out the WaterHeater:Mixed from the problem, I'm assuming it doesn't have a built in heater and is just served by the PlantComponent:TemperatureSource[1]
I'm writing the conclusion here because the section where I explain the sizing is lengthy
What you need to really remember: to size your hot water coil, the program actually gets user inputs defined in several objects and uses several sizing routines. It will use the design temperatures (and air flow rates in some cases) defined in the Sizing:Zone object and the resulting calculated laods, as well as the plant delta T you specify in Sizing:Plant.
It's up to you to determine whether you do need to feed information for the sizing routines to work properly.
My two cents is that if in your application the zone design temps aren't changing, and if you intend to keep the same constant delta T in the plant loop, you shouldn't need to feed new info for co-simulation.
If you do need to change it for the sizing routines, I'm sure there's a way (post a new question though).
For the sizing, it's done on the design days indeed.
It's going to size stuff in this order (that's what I understand at least): Zone, System (airloop), Component, and Plant. Important: please read more in the Sizing Manager section of the engineering reference.
(FYI, it's also going to start by looking at the global Sizing:Parameters)
First, it's going to size your zones, based on the Sizing:Zone (I/O) object, in which you enter the supply air temperature, humidity ratio, and potentially air flow rate (or tell it to calculate the air flow rate based on design days). That'll give you the heating and cooling loads.
You have no airloop here, so System is skipped.
Second, it's going to look at your components, in your case the ZoneHVAC:Baseboard:Convective:Water, and try to size the heating coil. The relevant section of the engineering reference is Coil:Heating:Water Sizing > Zone Coils
Get input from Zone Sizing
First, it gets a few input stored in the Zone Sizing routine in Zone Design Data Array (read for variable definition)
It gets the zone heating coil design air inlet temperature [C]:
$$T_{in,air} = DesHeatCoilInTemp_{zone}$$
This is calculated by checking the zone temp at sizing (from the Tstat), and the potentially Outside Air Fraction and temperature (at the design day).
And the zone design heating supply air temperature [C]:
$$T_{out,air} = HeatDesTemp_{zone}$$
This is directly entered in Sizing:Zone.
The zone heating coil design air inlet humidity ratio [kg/kg] will be used later for $cp,air$
$$W_{out,air} = HeatDesHumRat_{zone}$$
This is directly entered in Sizing:Zone.
Then the the zone design heating air mass flow rate in [kg/s]
\begin{equation} \dot mair,des = DesHeatMassFlow_{zone} \end{equation}
This is calculated from in the Zone Sizing, based on what's provided for air flow rate (can be a number, or "DesignDay" or "DesignDayWithLimit")
Size the coil
It then calculates the coil capacity:
\begin{equation} Qcoil,des = cp,air\dot mair,des\cdot (Tout,air - Tin,air) \end{equation}
Here $cp,air$ is calculated at the outlet humidity and the average of the inlet and outlet temperatures.
With the coil load and the user specified (in a Sizing:Plant object - important!) design hot water temperature decrease, calculate the max water flow rate:
\begin{equation} \dot Vcoil,water,max = Qcoil,des/(Cp,water\cdot \rho water\cdot \Delta Tplt,hw,des) \end{equation}
Documentation:
The design plant loop flow rates are set by the sum of the needs of the demanding components on each loop. For hot water loops that's the hot water coils.
What you need to really remember: to size your hot water coil, the program actually gets user inputs defined in several objects and uses several sizing routines. It will use the design temperatures (and air flow rates in some cases) defined in the Sizing:Zone object and the resulting calculated laods, as well as the plant delta T you specify in Sizing:Plant.
It's up to you to determine whether you do need to feed information for the sizing routines to work properly.
My two cents is that if in your application the zone design temps aren't changing, and if you intend to keep the same constant delta T in the plant loop, you shouldn't need to feed new info for co-simulation.
If you do need to change it for the sizing routines, I'm sure there's a way (post a new question though).
[1]You can read on how to autosize its built-in heater capacity using a WaterHeater:Sizing, which you'll want to set to Peak Draw given your specific application and carefully chose the indirect recovery time to determine the heater capacity needed.
| | 3 | No.3 Revision |
This a rather large question, and it's going to be hard to really explain in detail how the different sizing routines work and play together. That's why the Engineering Reference has such a huge section treating about sizing.
I'll do my best to get to the point and you'll have to forgive any gross simplification.
The first of such simplifications, is that I'll take out the WaterHeater:Mixed from the problem, I'm assuming it doesn't have a built in heater and is just served by the PlantComponent:TemperatureSource[1]
I'm writing the conclusion here because the section where I explain the sizing is lengthy
What you need to really remember: to size your hot water coil, the program actually gets user inputs defined in several objects and uses several sizing routines. It will use the design temperatures (and air flow rates in some cases) defined in the Sizing:Zone object and the resulting calculated laods, as well as the plant delta T you specify in Sizing:Plant.
It's up to you to determine whether you do need to feed information for the sizing routines to work properly.
My two cents is that if in your application the zone design temps aren't changing, and if you intend to keep the same constant delta T in the plant loop, you shouldn't need to feed new info for co-simulation.
If you do need to change it for the sizing routines, I'm sure there's a way (post a new question though).
For the sizing, it's done on the design days indeed.
It's going to size stuff in this order (that's what I understand at least): Zone, System (airloop), Component, and Plant. Important: please read more in the Sizing Manager section of the engineering reference.
(FYI, it's also going to start by looking at the global Sizing:Parameters)
First, it's going to size your zones, based on the Sizing:Zone (I/O) object, in which you enter the supply air temperature, humidity ratio, and potentially air flow rate (or tell it to calculate the air flow rate based on design days). That'll give you the heating and cooling loads.
You have no airloop here, so System is skipped.
Second, it's going to look at your components, in your case the ZoneHVAC:Baseboard:Convective:Water, and try to size the heating coil. The relevant section of the engineering reference is Coil:Heating:Water Sizing > Zone Coils
Get input from Zone Sizing
First, it gets a few input stored in the Zone Sizing routine in Zone Design Data Array (read for variable definition)
It gets the zone heating coil design air inlet temperature [C]:
$$T_{in,air} = DesHeatCoilInTemp_{zone}$$
This is calculated by checking the zone temp at sizing (from the Tstat), and the potentially Outside Air Fraction and temperature (at the design day).
And the zone design heating supply air temperature [C]:
$$T_{out,air} = HeatDesTemp_{zone}$$
This is directly entered in Sizing:Zone.
The zone heating coil design air inlet humidity ratio [kg/kg] will be used later for $cp,air$
$$W_{out,air} = HeatDesHumRat_{zone}$$
This is directly entered in Sizing:Zone.
Then the the zone design heating air mass flow rate in [kg/s]
\begin{equation} \dot mair,des = DesHeatMassFlow_{zone} \end{equation}
This is calculated from in the Zone Sizing, based on what's provided for air flow rate (can be a number, or "DesignDay" or "DesignDayWithLimit")
Size the coil
It then calculates the coil capacity:
\begin{equation} Qcoil,des = cp,air\dot mair,des\cdot (Tout,air - Tin,air) \end{equation}
Here $cp,air$ is calculated at the outlet humidity and the average of the inlet and outlet temperatures.
With the coil load and the user specified (in a Sizing:Plant object - important!) design hot water temperature decrease, calculate the max water flow rate:
\begin{equation} \dot Vcoil,water,max = Qcoil,des/(Cp,water\cdot \rho water\cdot \Delta Tplt,hw,des) \end{equation}
Documentation:
The design plant loop flow rates are set by the sum of the needs of the demanding components on each loop. For hot water loops that's the hot water coils.
[1]You can read on how to autosize its built-in heater capacity using a WaterHeater:Sizing, which you'll want to set to Peak Draw given your specific application and carefully chose the indirect recovery time to determine the heater capacity needed.
