Energy Plus & Open Studio Class Today, 5:45 PM Computer lab ECJ 3.402 Instructor: Wesley Cole

ASHRAE Student Chapter Meeting Monday Nov 26th at 6pm ECJ 5.410

Lecture Objectives: Finish with common HVAC system configurations Discuss control systems Discuss the life cycle cost analysis Learn about empirical modeling

HVAC systems in eQUEST

Basic purpose of HVAC control Daily, weekly, and seasonal swings make HVAC control challenging Highly unsteady-state environment Provide balance of reasonable comfort at minimum cost and energy Two distinct actions: 1) Switching/Enabling: Manage availability of plant according to schedule using timers. 2) Regulation: Match plant capacity to demand

Basic Control loop Example: Heat exchanger control Modulating (Analog) control air water Cooling coil x (set point temperature)

Cooling coil control valve Electric (pneumatic) motor Position (x) fluid Volume flow rate Vfluid = f(x) - linear or exponential function

The control in HVAC system – only PI Proportional Integral value Set point Proportional affect the slope Set point Integral affect the shape after the first “bump”

Detail control system simulation MatLAB - Simulink Control system simulation - take into account HVAC component behavior but focus more on control devices and stability of control scheme

Models integrated in HVAC System simulation Example: Economizer (fresh air volume flow rate control) Controlled device is damper - Damper for the air - Valve for the liquids fresh air damper mixing recirc. air T & RH sensors

HVAC Control Economizer (fresh air volume flow rate control) Controlled device is damper - Damper for the air - Valve for the liquids fresh air damper mixing recirc. air % fresh air T & RH sensors 100% Minimum for ventilation

Economizer – cooling regime How to control the fresh air volume flow rate? If TOA < Tset-point → Supply more fresh air than the minimum required The question is how much? Open the damper for the fresh air and compare the Troom with the Tset-point . Open till you get the Troom = Tset-point If you have 100% fresh air and your still need cooling use cooling coil. What are the priorities: - Control the dampers and then the cooling coils or - Control the valves of cooling coil and then the dampers ? Defend by SEQUENCE OF OERATION the set of operation which HVAC designer provides to the automatic control engineer % fresh air 100% Minimum for ventilation

Economizer – cooling regime Example of SEQUENCE OF OERATIONS: If TOA < Tset-point open the fresh air damper the maximum position Then, if Tindoor air < Tset-point start closing the cooling coil valve If cooling coil valve is closed and T indoor air < Tset-point start closing the damper till you get T indoor air = T set-point Other variations are possible Sequence of calculation in energy simulation modeling is different than sequence of operation ! We often assume perfect aromatic control

What are the reasons for energy simulations? System Development (research) Building design (evaluate different design solutions) Economic benefits Budget planning

Life Cycle Cost Analysis Engineering economics

Parameters in life cycle cost analysis Beside energy benefits expressed in $, you should consider: First cost Maintenance Operation life Change of the energy cost Interest (inflation) Taxes, Discounts, Rebates, other Government measures

Example Using eQUEST analyze the benefits (energy saving and pay back period) of installing - low-e double glazed window - variable frequency drive in the school building in NYC

What are the reasons for energy simulations? System Development (research) Building design (evaluate different design solutions) Economic benefits Budget planning

For budget planning Empirical model For average year use TMY2 Load vs. dry bulb temperature Measured for a building in Syracuse, NY Model For average year use TMY2 =835890ton hour = 10.031 106 Btu