The Curious Economics of Home Heat Todd Hixon Oasis October 26, 2010
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The Curious Economics of Home Heat
Todd Hixon
Oasis October 26, 2010
$5,000 Heat Bill
• 3,800 B2 house • InsulaDon not great
• Forced hot air: oil heat + AC
• Two systems: first & second floors
• Concord, MA
2
2007-‐2009 Energy Use
0
10
20
30
40
50
60
70
0
2
4
6
8
10
12
Nov Dec Jan Feb Mar Apr May-‐Oct
Oil Gal/d
kWh/d
HDD index
Summer AC Cost is a small % of total
3
Energy Units
• BTU (BriDsh Thermal Unit) is a measure of energy in the form of heat – Heat to raise temp of 1 lb of water by 1° F – Analogous to 1 calorie = heat 1 gm of water by 1° C
• KiloWae-‐hour (kWh) = unit of electrical energy – Can be converted to heat: 1 kWh delivered to a resisDve load releases 3,412 BTUs of heat
• Thermal efficiency = heat delivered to house ÷ heat released when fuel is consumed
4
Cost of Heat By Fuel Natural Gas Is The Obvious Choice
Wholesale Cost/unit
Retail Cost/unit
Units/ MMBTU
Thermal Efficiency
Cost/Usable MMBTU
Lb CO2/Usable MMBTU
Oil (gallon)
$2.284 $3.023 7.41 82.5% $27.11 1995
N Gas (therm)
$0.372 $1.493 10.00 87.5% $17.00 1345
Electricity (kWh)
$0.0431 $0.13 293.1 100% $38.10 1626
1) ISO New England 2) U.S. EIA: hep://www.eia.gov/pub/oil_gas/natural_gas/feature_arDcles/2010/ngyir2009/ngyir2009.html#markets 3) U. S EIA, June 2010: hep://www.eia.doe.gov 4) New York harbor spot price, 10/13/10 5) Naturalgas.org: hep://www.naturalgas.org/environment/naturalgas.asp#greenhouse/ 6) 81 lbs/MMBTU for New England electric system fuel mix ÷ 50% transmission loss factor.
5
Natural Gas / Oil Price RaDo Is VolaDle
0
20
40
60
80
100
120
07/08 08/09 Current
Retail N Gas $/M
MBT
U As % of O
il
6
Electricity and Heat Are Not Equivalent
• Electricity is a more useful form of energy – Converts efficiently to mechanical energy
• Electricity is a service – difficult and expensive to store – Value different at different Dmes
This makes a simple comparison of oil and electricity misleading
7
Heat Pump Physics
• Pumps heat into house – “recycles” lost heat
• Powered by electric motor
• Delivers ~3 heat units to house per unit of electrical energy
8
Heat Pump Economics
0
0.5
1
1.5
2
2.5
3
3.5
4
17 20 30 35 40 45 47
Outside Temperature (deg F)
Delivered Heat / Energy Used • 3x+ leverage • Called “Coefficient of
Performance” (COP) • LimitaDons:
– Throughput declines with outside temperature
– Delivers heat at ~95°F • Cheap supplemental heat
– Not enough to heat house in mid-‐winter
Source: Carrier 25HPA5H Spec Sheet
9
Electricity Is Cheap At Night
Marginal Cost ($/MWh)
Source: ISO New England, Weekly Market Summary, 9/27/10 10
Electricity Is Green At Night, Too
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
NE Electric Capacity Ordered By Variable Cost/MWh
Nuclear
Hydro, Wind, etc.
NGas -‐ CoGen
Coal
NGas -‐ Conv
Oil
3am Load
Average Daily Peak
Annual Peak
Source: NE ISO, Concord Municipal Light
Electricity costs in NE are Ded to N. Gas –the marginal supply most of the year
11
Concord Off-‐Peak Tariff
Cents/kWh
Peak Hours 13.4
Off-‐Peak Hours* 5.5
• Off-‐Peak = 11p-‐6a, 1p-‐3p, for residenDal heaDng & hot water
• Implemented via a 2nd meter + load controller that responds to a power-‐line carrier signal indicaDng peak/off-‐peak
12
Cost of Heat By Fuel
Wholesale Cost/unit
Retail Cost/unit
Units/ MMBTU
Thermal Efficiency
Cost/Usable MMBTU
Lb CO2/Usable MMBTU
Oil (gal) $2.284 $3.023 7.41 82.5% $27.11 1995
Gas (therm) $0.372 $1.493 10.00 87.5% $17.00 1345
Electric (kWh)
• Peak $0.0501 $0.130 293.1 100% $38.10 1626
• Off-‐Peak $0.0278 $0.055 293.1 100% $15.63 1127
• Heat Pump $0.0501 $0.130 293.1 300% $12.70 546
• RegulaDon $0.0109 $0.035 293.1 100% $9.95 1127
1) EsDmated from ISO New England data 2) U.S. EIA: hep://www.eia.gov/pub/oil_gas/natural_gas/feature_arDcles/2010/ngyir2009/ngyir2009.html#markets 3) U. S EIA, June 2010: hep://www.eia.doe.gov 4) New York harbor spot price, 10/13/10 5) Naturalgas.org: hep://www.naturalgas.org/environment/naturalgas.asp#greenhouse/ 6) 81 lbs/MMBTU for New England electric system fuel mix ÷ 50% transmission loss factor. 7) 56 lbs/MMBTU for New England electric system off-‐peak fuel mix ÷ 50% transmission loss factor. 8) EsDmated from ISO New England data 9) VCharge CorporaDon
13
Heat Pump & Off-‐Peak Can Be Combined
Heat provided by each system proporDonal to temperature liB
Heat Pump heats air to 95° F
Electric Thermal Storage (ETS) Tops Off Heat
Return Air @ 65° F
Supply Air @ 110° F
14
New System for Upstairs Heat Pump
(on right)
Electric Thermal Storage (ETS) Unit
15
Return air
Heat Pump Condenser
Brick Stack Air Handler Supply Air
Cost Model for Upstairs
• 51% cost savings • 63% of heat from Heat Pump
16
Results Measurement
• Oil deliveries • Separate meter for off-‐peak electricity
• Installed power meter on Heat Pump supply circuit
Current Sensors Power line communicaDons node
17
Results Measurement
• Power sensor on Heat Pump shows power usage
• Maintains hourly log file
18
QuanDtaDve Results
• Cost savings = 54% ($1,300) – Invested ~$3,000 over replacement cost of old system
• Saved 850 gal oil & 4.75 tons CO2
• Heat pump carries less of heat load than expected
19
Comfort Factor
• Electric heat is inherently cleaner and more reliable
• The heat pump is an awesome air condiDoner – Made light work of the 2010 heat
• It feels good to be green – Especially if you save money
• My wife gave the new system thumbs-‐up – More powerful air handler eliminated cold spots
20
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