HOME HEATING EFFICIENCY

IMPROVEMENT

Trevor ThompsonSenior Project II

Vermont Technical CollegeSpring 2011

Problem StatementInefficient heat distribution from the living room woodstove to

other rooms in the house resulting in ~7deg delta in temperature between the living room and the nursery (room 1).

Living Room~70 deg

~63 deg

Room 1Room 2

Room 3

Room 4

House Layout

Room 5

Solution Statement• Design a heat distribution system that takes heat provided from the living

room wood stove and distributes it to other rooms when called for.

• If the temperatures are not being met the controller will trigger the furnace to turn on and compensate.

Room 1

Room 4

Room 2Room 3

Living Room

Controller

V(T)

Actuator

room 5

Damper

V(T)V(T)

V(T)

V(T)

ActuatorDamper

Actuator Damper

ActuatorDamper

Damper

Furnace

Room 5

OutsideTemp

IntakeTemp

Project Plan

Mechanical Design

Step #1: Calculate Required Btu/hr

Formula:

BTU/hr Required = Volume of Room (ft3) X Insulation Rating + (# of Windows X 1000)

Length (ft) X Width (ft) X Height (ft)

* All Formula’s Obtained at www.engineeringtoolbox.com

Step #2: Determine Required Air Flow

23000 Btu/hr

1 kW (kJ/s) = 859.9 kcal/h = 3,413 Btu/h(23,000 Btu/hr) X (1kW/3413Btu/hr) = 6.76kW

Formula

~700 cfm Required

Air Flow (cfm) = [(6.76kW)(3.42)] / [(1.08)(30deg F)]

= 713 cfm

Step #3: Choosing Duct Size

Main Branch Duct Calculation

v = 900ft/minq = 700cfm *This will be used in the next step

Duct X-Sectional Area = 144 X (700cfm / 900ft/min) = 112in2

Area = pi X r2 so; r = sqareroot (Area / pi)

r = square root(112in2 / pi) = 5.97 inches

Duct Diameter = 12inches

• Air velocities in ducts should not exceed certain limits to avoid high pressure losses and unacceptable

noise generation.

Branch Duct Calculation

v = 400ft/minq = 78cfm

Duct X-Sectional Area = 144 X (78cfm / 400ft/min) = 28in2

Area = pi X r2 so; r = sqareroot (Area / pi)

r = square root(28in2 / pi) = 3 inches

Duct Diameter = 6 inches

Formula

Step 1: Determine Desired Air Velocity

Step 2: Calculate Duct Diameter

700 cfm

Friction Loss = [0.109136 X (700cfm)1.9 ] / (12in)5.02

Friction Loss = 0.1 inch H2O

Formula

Step #4: Determining Friction Loss in the Duct

Step #5: Choosing Fan

Confirmation that the existing duct can carry the same air volume as the new 12” round.

Step #6: Verifying Duct Equivalence

Step #7: Choosing Return Locations

What Do We Know?

• Each room has a fixed volume.

• As hot air is forced into the room existing cool air needs to be pulled out.

• Want air flow in each room to envelope the room with hot air to reduce cold air from penetrating the exterior walls.

• Since hot air rises I choose a low location for the return vent so the air that was force out was the cold air that resided in the room.

Solidworks Flow SimulationInitial Hot Air Vent Location

Final Hot Air Vent Location

SolidWorks Modeling

SolidWorks Modeling

12 inch Main Trunk6 in BranchesDampers

Actuator

Centrifugal Fan

Duct Intake

Main Existing Trunk

Transition Box

45deg Elbow

90deg Elbow

Controllable Damper Assembly

Damper

DamperDuct

Actuator

Controllable DamperAssembly

DamperAssembly

Complete SolidWorks Assembly

New Duct AssemblyExisting Duct Assembly

Combined Duct Assembly

Hot Air Control Vent System Level Diagram

Centrifugal Fan

Room 1 Actuator

Room 1 Damper

Room 2 Damper

Room 3 Damper

Room 4 Damper

Room 1 Temperatur

e Plate

Room 5 Relay

Room 5 Damper

Room 2 Actuator

Room 3 Actuator

Room 4 Actuator

Furnace

Computer

0-10V Signal

Ethernet Port

10K Type 3

24VAC

24VAC OutsideTemp

IntakeTemp

Room 2 Temperatur

e Plate

Room 3 Temperatur

e Plate

Room 4 Temperatur

e Plate

Room 5 Temperatur

e Plate

Electrical Wiring Diagram• Four wire to each actuator.

• Two wire to;1. Temperature Plates2. Fan Control3. Outside Temperature4. Intake Temperature5. Furnace

• Power to Fan.

• Power to Transformer.

• Tie into Controller

Furnace OA Temp Intake Temp

• 8 Universal Inputs• Temperature Plates (4)• Outside Air Temp Probe (1)• Intake Temp Probe (1)

• 4 Analog Outputs• Actuators (4)

• 4 Digital Relay Outputs• Furnace• Centrifugal Fan

• 15 VDC Out

• Ethernet Ports

• Battery Backup Pack

Controller Layout

Fabrication / Installation Process

1. Cut in zone control dampers and attach actuators

2. Install clearance extension

3. Install 90deg elbow

4. Install fan

5. Install 45deg tie-in elbow

6. Install back draft damper

7. Install 12” round duct pipe

8. Install Temperature Plates

9. Install Outside & Intake Temp Probes

Installation Process

Cross sectional area of intake must equal or exceed that of the 12’ round duct.

Clearance behind woodstove limits width to 4 inches.

Intake must travel from duct in basement through floor to rear of woodstove.

Design must include a removable filter to remove dust/ash/smoke before going through system.

Area of 12” Round Duct = (pi)r2 = pi x 62 = 113.1 in2

Area Intake = Length X Width

Length = 113.1 in2 / 4in = 28.3 in ~29 inches

Designing Intake

1. Find location of woodstove in the basement

2. Review basement layout for any obstructions

3. Determine where to tie into existing duct

Initial Design Verification

Initial Sketch of Intake

Controller Wiring

Run Trunk Line / Install Mounting Board

Mount Controller

Connect Wires to Terminals

List of Materials / BOM

Demo

Questions