feasibility of retrofitting centralized hvac systems for...

Feasibility of Retrofitting Centralized HVAC Systems for Room-Level Zoning

Tim Sokoor, Brian Holben, Kamin Whitehouse

Work of:Link Lab @ University of Virginia

Presented by:Rakan Alseghayer

Energy Consumption§ Distribution of energy consumption In the paper (2012):

– US: 43%– Canada and UK > 60%

§ 2015 in the US: 37%

§ U.S. Department of Energy (DOE), Energy Information Administration (EIA) (2015) Annual Energy Outlook 2015

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Home HVAC Zoning

§ Usually floor level zoning– Bedrooms in upper floor– Living areas in bottom

§ Each zone has a separate thermostat.

§ Aiming for comfort, and not energy savings.

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Commercial Buildings HVAC Zoning

§ Discharge Air Regulations Technique (DART)– Fan speed controlling– Ex: Millenial Net, Siemens APOGEE, etc

§ Micro-environment systems:– Fine-grained temperature control (typically a desk).– Ex: Johnson Controls, InterfaceAR, etc

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HVAC Zoning Shortcomings§ Commercial:

– Expensive and hard to result in investment return.– In micro-environments reaches 20K and 100K per desk!

§ Homes:– Expensive and difficult to retrofit an existing system.

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Existing Studies§ Single room and small areas:

– Conc: efficiency loss.– But: How about the savings?

§ Room-level zoning VS house level:– Conc: less energy to change a zone by a dgree than a whole

house.– But: Maintaining that degree?

§ Occupancy-based room-level zoning:– Occupancy prediction of the whole house.– But: across rooms interactions and patterns?

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Goal and Approach§ Goal:

– Achieving room-level zoning by using cheap sensors and actuators to retrofit an existing HVAC system.

§ Approach: – Conducting a pre-analysis study for the feasibility of

such system.– Implementation and evaluation of such system with

occupancy model.

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Outline§ Motivation

§ Prelim Studies§ Challenges§ Implementation and Evaluation§ Future Directions§ Conclusions

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HVAC Size§ Does oversized HVAC systems reduce the energy

saving potential?§ EnergyPlus simulation of different buildings with same

HVAC size.

§ Energy gain outweighs efficiency loss for small spaces.

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Efficiencyloss

Thermal Leakage§ EnergyPlus simulation of two rooms in a building.§ Heat one room with different layouts.§ energy reduced as the exterior walls reduce.

§ Energy Gain is not eliminated by thermal leakage.

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Room Occupancy§ Particular rooms are occupied at certain times.

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Outline§ Motivation§ Prelim Studies

§ Challenges§ Implementation and Evaluation§ Future Directions§ Conclusions

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Back Pressure§ HVACs have different stages of operation with different

air-flows.– Ex: stage 1 à 830 CFM – stage 2 à 1200 CFM

§ Ductwork is designed to accommodate air-flow which is different in each stage.

§ If air-flow is not released through registers Back Pressure happens:– increase leakage through cracks in ducts.– Damage HVAC parts.

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Short Cycling§ Minimum time of operation during a stage is highly

recommended before transitioning between stages in HVAC.

§ Transitioning without going through the minimum time can increases wear and tear of HVAC.

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Occupancy§ Reactive occupancy:

– Operates when there is an active occupancy in a room or house.– Drawbacks: when a lot of activity is in place, it acts as a whole

house HVAC, and can result in short cycling.

§ Predictive:– Ahead of time operation based on predictions to avoid short

cycling.– Drawback: need a lot of historical data for precision.

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Outline§ Motivation§ Prelim Studies§ Challenges

§ Implementation and Evaluation§ Future Directions§ Conclusions

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Temperature HW§ 21 off-the-shelf sensors from La Crosse Technology.§ BAYweb Internet-controllable thermostat.

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Air-Flow Control HW§ Active registers and dampers integrated with a wireless

control system.§ Retrofitted and designed active registers.§ TelosB mote used for wireless communication.§ Airflow validation through Kestrel 4100 Pocket Air Flow

Tracker.

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Temperature Sensing§ External wall has erratic readings and not a good

reflective of the interior temperature– Due to direct air flow from ducts and heat around windows.

§ Zone temperature is the average of its interior walls readings

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Air-Flow Efficiency§ Cooling only half of the house doesn't result in double

airflow in the other half.– Due to air loss from back pressure, and duct friction, and air

leakage.§ Closing registers reduces the air-flow as well as the

efficiency.

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HVAC Controlling

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§ Simple HVAC controlling states.

§ Float: turn off§ Hold: maintaining the temperature.§ Cool1: stage 1 cooling.§ Cool2: stage 2 cooling.

The Building§ 1400 sqf, single floor, 7-rooms, 2 zones.§ Red is zone 1 (living area).

– Conditioned 8:00am to 9:30pm§ Blue is zone 2 (bedroom area).

– Conditioned 12:00am to 8:00am

§ Both zones conditioned between 9:30pm and 12am.

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Experiment§ 20 days duration.§ Running 2 systems (10 days each):

– Sub zoned and single zoned§ Each system run every other day such that weather

factor is minimized.§ Energy was monitored by The Energy Detective device.

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Consumed Energy§ Average energy saved by sub-zoning is ~20%

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Room Temperatures§ Temperature in non-conditioned rooms is higher than

others.

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Air-Flow in Zones§ Closing other registers increase the flow in others.§ Inactive zones still have air flow, however, have no

substantial effect.

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Outline§ Motivation§ Prelim Studies§ Challenges§ Implementation and Evaluation

§ Future Directions§ Conclusions

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Occupancy Prediction§ Stay Tuned J

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Other Building Layouts

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§ Office buildings consumption§ What about apartments?§ Scalability?

GW Architectures§ We looked at centralized architectures for a house, how

to scale that to larger buildings?§ Hierarchical structure of GWs can be employed. (Slave

master).

§ Fault tolerance has to be taken into consideration.

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M

S

S

HVAC

Analytics On Data§ Through collected, we can apply some analytics that

further save more energy:– Observe the temperature changing behavior.– Occupancy information.– Feedback for efficiency (too much energy cosumed during a

specific time)

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Current Zoning Systems§ Lennox and many other vendors.

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Conclusions§ Feasibility study of the potential energy savings in

homes through room-level zooning is promising.

§ A prototype of COTS hardware (< $500) was implemented and evaluated in a 7-room 1400 sqf house which is a single floor divided into 2 zones.

§ Results show a ~20% gain of energy comparing with the whole floor zoning.

§ Further challenges have to be addressed.

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Questions?Thank you J