Lecture Objectives:

• Clarify issues related to eQUEST – for midterm project

• Learn more about various HVAC - economizer

- heat recovery

• Discuss about the final project assignment

Integration of HVAC and building physics models

BuildingHeating/Cooling

SystemPlant

Load System Plant model

Qbuiolding Q

including

Ventilation

and

Dehumidification

Primary and Secondary Building Systems

AHU

ECJ buildingCooling(chiller)

(or Gas)

Electricity

Gas

Heating(boilers)

Fresh air For ventilation

Distribution systems

Air transport

Secondary(HVAC) systems

Primary (Plant)systems

AHU – Air Handling Unit

Processes in AHU

filterfan

cooling coil

heating coil

filter steamhumidifier

Building

mixing

damper fresh air

Processes in AHU presented in psychrometric chart - cooling

OA Case forSummer in Austin

IA

MA

SA

Processes in AHU presented in psychrometric chart - heating

OA

Case forWinter in Austin

IA

MA

SA

Simple modeling of HVAC system

Models for heat transfer in building elements

-External boundaries (weather data)- convection - conduction - radiation - infiltration

QLoad – for every hour

Does not include ventilationby HVAC system

)(/

)()(/

)()(

sup

sup

sup

airpLoadindoorply

plyindoorairpLoad

plyindoorairpLoad

cVQTT

or

TTcQV

or

TTcVQ

Disadvantages of this model:- Does not include the characteristics of HVAC components- Assume that whole building is a single zone- Assume always all air system

Supply volume flow rate for every hour

Psychrometric Chart

- External boundaries (weather data)- Points in chart - Heating, cooling, mixing, humidification, dehumidification- Find enthalpies and V

QHVAC – for every hour

VAV

Supply temperature for every hour

CAV

Final project topics:Software based• Energy analysis of building form Integrated design course, • Envelope analysis of glass buildings• ….

Detail Modeling (your model)• Heat recovery systems, • Economizers, • Water cooled chiller,• Geothermal heat pump, • Solar hot water systems,• Mass transfer (moisture, ozone, VOCs,…) • ….Your ideas

Requirement for Thursday Email me:• Group members • Project title• One paragraph (200-300 words) including

- Project objective - Methodology- Expected results

Any schematic drawing is welcome

Thursday afternoon long office hours to discuss

your project

Modeling of AHU systemEconomizers & Heat recovery systems

IA

OAsummer

OAwinter

OA

What to do if OAIs here ?

Economizer

mixing

damper

fresh air

T & RH sensors

recirc. air

Controlled devices are damper

Economizer Fresh air volume flow rate control

mixing

damper

Fresh(outdoor) air

T & RH sensors

Recirc. air

% fresh air

Minimum for ventilation

100%

TOA (hOA)

enthalpy

Economizer – cooling regime with CAV

How to control the fresh air volume flow rate?

% fresh air

Minimum for ventilation

100%

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

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

Heat Recovery SystemsAir to Air Heat Exchanger

Plate heat exchangers

Enthalpy wheel Effectiveness ~60%

Effectiveness ~75%

Effectiveness ~50%

Ventilation Heat Recovery Systemsfor cooling and heating

Commercial buildings Residential buildings

Saving % - depends on how much ventilation we have in the building

Water Cooled Chiller

Outside air 95°F

Inside 75°FWater 42°F

BuildingWater 52°FWater 120°F

Water 100°F

Cooling tower

Chiller

Task: analyze COP for the whole yearand different locations

Solar hot water system

Geothermal Energy Systems(in combination with a cooling machine / heat pump)

Summer Winter

In the summer, the earth acts as a cooling tower. The Cooling Machine loads the loop with heat, sending warmed water to be cooled by the earth

In the winter, the earth acts as the boiler. The Heat Pump extracts heat from the loop, sending cooled water to be warmed by the earth.