Question-and-Answer Resource for the Building Energy Modeling Community
Get s tarted with the Help page
 Ask Your Question

# How can I simulate a CoolingCoilDX with a high air flow (rated air volume flow rate)?

I'm simulating a DataCenter equipped with CRACs. These devices have a very high rated air volume flow rate. For the equipment I'm using the ratio is 0.00006822 m³/s per W (0.2456 m³/h per W or 865 m³/h per TR).

The problem is that the equipment Coil:Cooling:DX:SingleSpeed accepts a maximum 0.00006041 m³/s per W and when I put a higher flow relation than this, EnergyPlus reports an error that the flow ratio by load is higher than the maximum acceptable.

** Severe  ** Sizing: Coil:Cooling:DX:SingleSpeed "CRAC - DATA CENTER": Rated air volume flow rate per watt of rated total cooling capacity is out of range.
**   ~~~   ** Min Rated Vol Flow Per Watt=[4.027E-005], Rated Vol Flow Per Watt=[6.821E-005], Max Rated Vol Flow Per Watt=[6.041E-005]. See Input Output Reference Manual for valid range.


Is there any other component in EnergyPlus that properly represents a CRAC and supports a greater rated air volume flow rate ratio?

edit retag close merge delete

## 1 Answer

Sort by » oldest newest most voted

There are actually 2 limits on DX coil flow/capacity. One is for rated capacity/sizing, and the other is for operating performance.

The limits are as follows:
1) min/max rated flow/capacity
2) max flow/capacity in cooling or heating mode
3) min flow/capacity in either mode

// Airflow per total capacity range (Regular DX coils)
Sizing Constraints:
Real64 const MaxRatedVolFlowPerRatedTotCap1( 0.00006041 ); // m3/s per watt = 450 cfm/ton
Real64 const MinRatedVolFlowPerRatedTotCap1( 0.00004027 ); // m3/s per watt = 300 cfm/ton
Operating Constraints:
Real64 const MaxHeatVolFlowPerRatedTotCap1( 0.00008056 ); // m3/s per watt = 600 cfm/ton
Real64 const MaxCoolVolFlowPerRatedTotCap1( 0.00006713 ); // m3/s per watt = 500 cfm/ton
Minimum limit:
Real64 const MinOperVolFlowPerRatedTotCap1( 0.00002684 ); // m3/s per watt = 200 cfm/ton


What this means is that the DX coil can be sized to meet the coil sizing requirements, and then simulated to meet the operational requirements (which may exceed the rated requirements).

If you autosize a DX coil you will get a capacity and air flow rate that are constrained to the min/max "rated" flow/capacity limits.

Coil:Cooling:DX:SingleSpeed, ( child object that is used in parent "wrapper")<br>
Furnace ACDXCoil 1,      !- Name<br>
FanAndCoilAvailSched,    !- Availability Schedule Name<br>
autosize,                   !- Gross Rated Total Cooling Capacity {W}<br>
autosize,                    !- Gross Rated Sensible Heat Ratio<br>
3.0,                     !- Gross Rated Cooling COP {W/W}<br>
autosize,                    !- Rated Air Flow Rate {m3/s}<br>


If you also autosize the parent object (one that also has a flow rate input), then you will get the same capacity and flow values as with the child component. The parent objects do not have a capacity input since the child component specifies that performance aspect.

However, if you do not autosize the parent object, and that parent has a flow rate input field, then you can operate the coil "outside" the rated flow/capacity limits. If the parent object does not provide a flow rate input, then the only constraint is with the child component (i.e., the DX coil) and you cannot exceed the rated flow/capacity limit. If the parent does have these inputs, then you can operate the DX coil outside the rated limits.

As an example, the DX coil shown above was either autosized, or hard sized. That coil was then configured in a unitary system parent object. The parent then selects the air flow rate to operate during the simulation. During sizing, the child (the DX coil) uses the "rated" flow/capacity limits. During the simulation, the parent uses the operating flow rate specified.

This way one can select a component with certain design specifications, and operate that component at "off design" operation. For example, I pick a coil with 400 cfm/ton, and then operate that coil at 450 cfm/ton.

Assume here that the DX coil had a 1.5 m3/s design flow rate. In this parent a flow rate of 1.6 m3/s is specified.

AirLoopHVAC:Unitary:Furnace:HeatCool, ( parent object that ...
more

## Comments

Did not get an answer, can someone clarify how parent object should changed if DXcoil is set to autosized. Can be CoilSystem:Cooling:DX be counted as parent object?

( 2018-02-22 11:57:07 -0600 )edit

CoilSystem:Cooling:DX does count as a parent object but does not have operating air flow rate inputs (the furnaces and unitary systems do have these inputs). If the parent object has these inputs then input the operating air flow rate in the parent and the coil will operate at higher m3/s/W (CFM/ton) air flow rates. If the parent does not have air flow rate inputs, then something else in the program needs to set the flow rate, probably the terminal units.

( 2018-02-22 12:04:53 -0600 )edit

## Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

## Stats

Asked: 2015-08-20 17:35:27 -0600

Seen: 900 times

Last updated: Feb 02 '16