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 Building Heating/Cooling System Plant Load System Plant model Q buiolding Q including Ventilation and Dehumidification

Primary and Secondary Building Systems AHU ECJ building Cooling (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 filter fan cooling coil heating coil filter steam humidifier Building mixing damper fresh air

Processes in AHU presented in psychrometric chart - cooling OA Case for Summer in Austin IA MA SA

Processes in AHU presented in psychrometric chart - heating OA Case for Winter 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 Q Load  – for every hour Does not include ventilation by HVAC system 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 Q HVAC  – 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 me: Group members Project title One paragraph ( words) including - Project objective -Methodology -Expected results Any schematic drawing is welcome Thursday afternoon long office hours to discuss your project

Modeling of AHU system Economizers & Heat recovery systems IA OA summer OA winter OA What to do if OA Is 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% T OA (h OA ) enthalpy

Economizer – cooling regime with CAV How to control the fresh air volume flow rate? % fresh air Minimum for ventilation 100% If T OA < T set-point → Supply more fresh air than the minimum required The question is how much? Open the damper for the fresh air and compare the T room with the T set-point. Open till you get the T room = T set-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 T OA < T set-point open the fresh air damper the maximum position Then, if T indoor air < T set-point start closing the cooling coil valve If cooling coil valve is closed and T indoor air < T set-point start closing the damper till you get T indoor air = T set-point Other variations are possible

Heat Recovery Systems Air to Air Heat Exchanger Plate heat exchangers Enthalpy wheelEffectiveness ~60% Effectiveness ~75% Effectiveness ~50%

Ventilation Heat Recovery Systems for 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°F Water 42°F Building Water 52°FWater 120°F Water 100°F Cooling tower Chiller Task: analyze COP for the whole year and 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.