Objectives Propose residential system related final project –Compare VAV systems with DOAS systems

One more project topic Residential system with mechanical ventilation –Analyze operation of the heat recovery system Heating Cooling 72ºF OA 72ºF Outdoor Air Exhaust Fresh Air

Commercial Project Zone orientation Commercial building Base size is ft x ft with perimeter zone depth of ft. Floor to floor is 12 ft and floor to suspended ceiling is 9 ft.

Project Cooling and heating load for each zone and whole building: Fresh air requirement based on number of occupants: To provide acceptable IAQ in the building, ventilation system supply minimal amount of fresh air is in all spaces (except plenums) that produce 0.2 ACH.

VAV System Terms & Equations (you can find them in ASHRAE Standard 62) Fraction of minimum outdoor air in space/zone supply air X i = V OAi / V SAi Critical space Space with maximum X i, Z=max ( X i ) Fraction of outdoor air in system supply air X = sum(V OA ) / sum(V SA ) Required Fraction of outdoor air: Y=X/(1+X-Z)

Other Issues Related to VAV Reheaters (sizing and control) Fan control Minimum supply air Occupancy sensors Some references at:

DOAS with multi-split systems Fresh air?

DOAS fresh air configurations

Issues Related to DOAS Split of sensible and latent load Selection of hydronic system Winter vs. summer operation –Winter operation with DX systems (heat pump)

Sequence of operation for the control system design mixing CC OA RA SA HC Adiabatic humidifier Define the sequence of operation for: WINTER operation and: - case when humidity is not controlled - case when humidity is precisely controlled Solution on the whiteboard

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 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