Lecture 22: Primary System Loops in EnergyPlus Notes: __________________________________________________________________ ________________________________________________________________________ Material prepared by GARD Analytics, Inc. and University of Illinois at Urbana-Champaign under contract to the National Renewable Energy Laboratory. All material Copyright 2002-2003 U.S.D.O.E. - All rights reserved

Purpose of this Lecture Gain an understanding of: Water (fluid) side loop structures in EnergyPlus How to control fluid flow rates using the EnergyPlus pump strategies

Defining Loops Loops define the movement of mass and energy within an HVAC system Plant loop Condenser loop Heat recovery loop Systems defined by the order of branches/components on the HVAC loop

Defining Loops (cont’d) Main loops divided into “sub-loops” or “semi-loops” for organizational clarity & simulation logistics Sub-loops are matched pairs that consist of half of the main loop. For example, plant and condenser loops are broken into supply and demand sides.

Demand- & Supply-Side Sub-Loops Plant demand-side sub-loop contains equipment that creates a load on the plant. Plant supply-side sub-loop contains equipment that meets these loads. Each supply-side sub-loop must be connected to a demand-side loop.  

Demand- & Supply-Side Loops (cont’d) Heating Coil HW Pump Outlet Node ± HW Pump HW Demand Outlet Node Boiler Inlet Node HW Supply inlet Node Heating Coil Inlet Node Exit Pipe Boiler Heating Coil Outlet Node Inlet Pipe HW Supply Outlet Node HW Demand Inlet Node Boiler Outlet Node HW Supply Outlet Pipe Demand-Side Loop Supply-Side Loop

Branches for Water-Side Loops Maximum Branch Flow Rate (Ignored) Comp1 Type Comp1 Name Comp1 Inlet Node Name Comp1 Outlet Node Name Comp1 Branch Control Type

Branches for Water-Side Loops - Example Heating Supply Inlet Branch, !- Branch Name , !- Maximum Branch Flow Rate {m3/s} PUMP:VARIABLE SPEED, !- Comp1 Type HW Circ Pump, !- Comp1 Name HW Supply Inlet Node, !- Comp1 Inlet Node Name HW Pump Outlet Node, !- Comp1 Outlet Node Name ACTIVE; !- Comp1 Branch Control Type

Layout for Individual HVAC Supply or Demand Sub-Loops Elements can be defined in series, in parallel, or both with some restrictions Branches are defined as individual legs within the loop structure Segment between point A & B is defined as a branch, as is the section between points E and F

Layout for Individual HVAC Supply or Demand Sub-Loops The first supply side component between A & B must be the loop pump, which controls the loop flow. There may be multiple branches between the splitter and mixer (between points C1 & D1 to Cn & Dn). Each sub-loop may only have one splitter and one mixer.

Layout for Individual HVAC Supply or Demand Sub-Loops Equipment may be in parallel between the mixer and splitter, Within any branch, there can only be elements in series. Sub-loops do not require a splitter or mixer, if all equipment on the sub-loop is in series—a single branch defines the entire sub-loop.

Pumping Rules Pumps must be on the supply side Splitter Mixer Components Loop Pump From Demand- Side Sub-Loop To Demand- Side Sub-Loop Supply-Side Sub-Loop Pumps must be on the supply side Pumps can operate as constant or variable flow Pumps can run continuously or intermittently

Pumping Rules (cont’d) Single boiler/chiller with NO bypass, PUMP:CONSTANT SPEED Boiler/chiller should be constant flow Pump should be intermittent Single boiler/chiller with NO bypass, PUMP:VARIABLE SPEED Boiler/chiller should be variable flow, regardless of whether pump is intermittent or continuous (runs at the minimum if demand is less than minimum, this includes zero.)

Pumping Rules (cont’d) Single boiler/chiller with bypass, PUMP:CONSTANT SPEED Boiler/chiller can be constant or variable flow Pump may be intermittent or continuous as long as the bypass can handle the entire pump volume when the boiler is not operating

Pumping Rules (cont’d) Multiple branches add more complexity, but it is nothing more than continuity. If the pump is putting out flow then it has to have a branch to flow down whether it is a chiller or a bypass.

Pumping Rules (cont’d) You are always safer adding the bypass for a simulation. If the active machines require the flow the bypass will be dry Thermodynamically it does not make any difference if the flow goes through a machine that is OFF or it flows down the bypass. There is no pressure simulation and flow losses are not accounted for.

Summary of Loop Limitations Each sub-loop allowed one splitter and one mixer One bypass on each sub-loop optional No other components may be in series with a bypass Equipment may be in parallel only between the splitter and mixer Equipment may be in series in each branch

3-Zone VAV System We are going to look at this system input Loop by Loop

Cooling Coil & Chilled Water Demand Side

Cooling Coil & Chilled Water Demand Side Objects required: BRANCH LIST CONNECTOR LIST SPLITTER MIXER BRANCH, VAV Sys 1 ChW-Branch COIL:Water:DetailedFlatCooling, VAV SYS 1 Cooling Coil

Cooling Coil & Chilled Water Demand Side (cont’d) Objects required (cont’d): BRANCH, Chilled Water Loop 1 CHW Inlet Branch PIPE BRANCH, Chilled Water Loop 1 CHW Outlet Branch BRANCH, Chilled Water Loop 1 CHW Bypass Branch

Hot Water Demand Side

Hot Water Coils & Demand Side Objects required: BRANCH LIST CONNECTOR LIST SPLITTER MIXER BRANCH,Zone X Reheat Branch (3) COIL:Water:SimpleHeating(3) BRANCH, HW Outlet Branch PIPE BRANCH, HW Inlet Branch BRANCH, HW Bypass Branch

Hot Water Loop Supply Side

Hot Water Loop Supply Side Objects required: PLANT LOOP BRANCH LIST CONNECTOR LIST SPLITTER MIXER BRANCH, Supply Inlet Branch PUMP:VARIABLE SPEED Boiler Plant Demand Side Heating Loop Outlet Node HW Pump HW Pump Outlet Node Bypass Boiler Inlet Node HW Supply Inlet Node HW Supply Outlet Node

Hot Water Loop Supply Side Hot Water Loop Supply Side (cont’d) Hot Water Loop Supply Side Objects required: BRANCH, Boiler Branch BOILER:SIMPLE BRANCH, Supply Bypass Branch PIPE BRANCH, Supply Outlet Branch PLANT OPERATION SCHEME HEATING LOAD RANGE BASED OPERATION HEATING LOAD RANGE EQUIPMENT LIST Boiler Plant Demand Side Heating Loop Outlet Node HW Pump HW Pump Outlet Node Bypass Boiler Inlet Node HW Supply Inlet Node HW Supply Outlet Node

Chilled Water Supply Side

Chilled Water Supply Side Plant Supply Side Cooling Loop CW Pump Chiller Bypass Plant Demand Side Cooling Loop Objects required: PLANT LOOP, Chiller Plant Chilled Water Loop BRANCH LIST CONNECTOR LIST SPLITTER MIXER

Chilled Water Supply Side (cont’d) Plant Supply Side Cooling Loop CW Pump Chiller Bypass Plant Demand Side Cooling Loop Objects required (cont’d): BRANCH, Chiller Plant Cooling Supply Inlet Branch PUMP:VARIABLE SPEED BRANCH, Chiller Plant Chiller Branch CHILLER:Electric BRANCH, Chiller Plant Cooling Supply Bypass Branch PIPE

Chilled Water Supply Side (cont’d) Plant Supply Side Cooling Loop CW Pump Chiller Bypass Plant Demand Side Cooling Loop Objects required (cont’d): BRANCH, Chiller Plant Cooling Supply Outlet Branch PIPE PLANT OPERATION SCHEMES COOLING LOAD RANGE BASED OPERATION COOLING LOAD RANGE EQUIPMENT LIST

Condenser Loop Demand Side

Condenser Loop Demand Side Objects required: BRANCH LIST CONNECTOR LIST SPLITTER MIXER BRANCH, Condenser Demand Inlet Branch PIPE BRANCH, Chiller Condenser Branch CHILLER:Electric BRANCH, Cond. Demand Bypass Branch BRANCH, Cond. Demand Outlet Branch Plant Supply Side Cooling Loop Chiller Condenser Supply Side Loop Condenser Bypass

Condenser Supply Side

Condenser Loop Supply Side Condenser Supply Side Condenser Loop Supply Side Cooling Tower Condenser Pump Condenser Bypass Condenser Demand Side Loop Objects required: CONDENSER LOOP BRANCH LIST CONNECTOR LIST SPLITTER MIXER BRANCH, Supply Inlet Branch PIPE BRANCH, Condenser Branch COOLING TOWER:Single Speed

Condenser Loop Supply Side (cont’d) Condenser Supply Side Condenser Loop Supply Side (cont’d) Cooling Tower Condenser Pump Condenser Bypass Condenser Demand Side Loop Objects required (cont’d): BRANCH, Cond. Supply Bypass Branch PIPE BRANCH, Supply Output Branch CONDENSER OPERATION SCHEMES COOLING LOAD RANGE BASED OPERATION LOAD RANGE EQUIPMENT LIST

Summary Loops are backbone of HVAC simulation all equipment attached to air or fluid loops Loop structure permits assembly of any system through input—not hardwired Primary system may consist of four different loops: plant supply and demand, condenser supply and demand Pumps regulate flow while attempting to meet requests on both sides of each loop pair Individual loops may have components in series and parallel with some limitations