Lecture Objectives: Analyze several modeling problems –Examples from the final project list Economizer Solar collectors Phase change thermal storage materials

Example 1: HVAC Control Economizer (fresh air volume flow rate control) mixing damper fresh air T & RH sensors recirc. air % fresh air Minimum for ventilation 100%

Economizer – cooling regime How to control 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 the 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 Sequence of calculation in energy simulation modeling is different than sequence of operation ! We often assume perfect aromatic control

Solar radiation Storage tank Perforated tube City water T2 Example 2: Solar Collector T1 Bathroom

Solar collectors Storage tank Flat plateEvacuated tube

Solar collector system Solar collector Water flow Water tank Area Property of solar collector (collector heat removal factor) Total solar radiation coefficient which define lost of energy from solar collector surfaces to surrounding define lost of energy from water tank to surrounding Used energy

More details about hot water system

Example 3: Phase change materials -Next generation of energy efficient building materials -Integrate phase change materials (PCMs) to insulation -Reduce peak heat transfer rates across walls and ceilings, -Shift peak cooling loads and reduce size of equipment, -Large potential for reduction of energy use, -Use nanotechnology, -Can be used in insulation or any other building material.

You need to evaluate potential for reduction of energy use with p hase change materials Howe would you model phase change materials integrated into building materials?