Final Projects Grading criteria is posted on the course website Preliminary results are due Next Tuesday Final Project delivery on Monday Dec. 7 th –Final Project presentation at noon

Field Trip to the central cooling and power plants Monday, November 30: anytime in the afternoon Thursday, December 3: 8-9:30 a.m. or 1- 2:30 p.m. or 1:30-3 p.m. Friday, December 4: p.m.

Objectives Finish with design of VAV and DOAS System Control

Other building load calculation tools

Cooling and Heating Loads from eQUEST Zone orientation 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.

Example of Cooling and Heating Loads Cooling and heating load for each zone and whole building: Fresh air requirement based on number of occupants:

Ventilation Loads asses/ARE389H/Handouts/Std pdf

VAV System

VAV Example -One system -Multiple Spaces/Zones - VAV box for each space/zone

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)

Example Solution Space1Space 2Space 3Space 4 V SA V OA Xi X Z Y

Other Issues Related to VAV Fan control Minimum supply air Occupancy sensors

VAV with fan terminal units

DOAS System

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)

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

HVAC Control Example 2: Dew point control (Relative Humidity control) filter fan cooling coil heating coil filter mixing damper fresh air T & RH sensors We either measure Dew Point directly or T & RH sensors substitute dew point sensor Humidity generation Heat gains We should supply air with lower humidity ratio (w) and lower temperature

Relative humidity control by cooling coil T DP Mixture Cooling Coil Room Supply Heating coil

Relative humidity control by cooling coil (CC) Cooling coil is controlled by T DP set-point if T DP measured > T DP set-point → send the signal to open more the CC valve if T DP measured < T DP set-point → send the signal to close more the CC valve cooling coil heating coil mixing Fresh air T air & T DP sensors Control valves Heating coil is controlled by T air set-point if T air < T air set-point → send the signal to open more the heating coil valve if T air > T air set-point → send the signal to close more the heating coil valve

Sequence of operation (ECJ research facility) Control logic: Mixture in zone 1: IF (( TM<TSP) & (DPTM<DPTSP) ) heating and humidifying Heater control: IF (TSP>TSA) increase heating or IF (TSP<TSA) decrease heating Humidifier: IF (DPTSP>DPTSA) increase humidifying or IF (DPTSP<DPTSA) decrease humid. Mixture in zone 2: IF ((TM>TSP) & (DPTM<DPTSP) ) cooling and humidifying Cool. coil cont.: IF (TSP TSA) decrease cooling Humidifier: IF (DPTSP>DPTSA) increase humidifying or IF (DPTSP<DPTSA) decrease hum. Mixture in zone 3: IF ((DPTM>DPTSP) ) cooling/dehumidifying and reheatin Cool. coil cont.: IF (DPTSP>DPTSA) increase cooling or IF (DPTSP<DPTSA) decrease cooling Heater control: IF (TSP>TSA) increase heating or IF (TSP<TSA) decrease heating Set Point (SP) Mixture 2 Mixture 3 Mixture 1 DBT SP DPT SP