Ground Source Heat Pumps – Design for Performance...ELT EST, F LLT COP kW LST kW kW kW COP 80 30 87 4.1 2.1 24 interpolated 45 89 5.1 2.1 38 0.50 0.3 2.9 3.6 50 90 5.4 2.1 42 100

Ground Source Heat Pumps –Design for Performance

Andy ShapiroEnergy Balance, Inc.

andy@energybalance.us

Ground Source Heat Pumps – Design for Performance

• Part I – Basics of systems, houses and summary of results

• Part II – Details of systems design and data collected

• My limited experience• Data is a work in progress

Ground Source Heat Pumps – Design for Performance

• Part I – Basics of systems, houses and summary of results

Credits

• Design: Tom Reilly, Salem Engineering and Marc Rosenbaum, Energysmiths

• Install: E&M Mechanical, VT Energy Contracting, Spafford Well

• Construction: Bill Heigis and Hobie Guion, Chuck Reiss, Jim Huntington

The HousesHouse Name Stone Pill Knight Location E.Montpelier VT Charlotte VT Hinesburg VTSquare feet 2,308 2,800 1,800 Design load, BTU/hr 25,000 28,000 26,000 Modeled annual heat load, MMBtu/yr

37 29 34

Renewable Electric 6 kW PV 10 kW Wind 3 kW PV

Pill - Maharam House

Pill - Maharam House

Knight House

Atwood-Stone House

The Houses

• Lots of insulation –– (worry about details)

The Houses • Great windows

Fiberglass frame window -- ALL thermal break! (Accurate Dorwin, Thermotech)

The Houses• Super air tight • Pill house –

~500 cfm-50

The Houses• Recover

energy where possible –

• Drain-water + Heat Recovery Ventilation

• Renewable electricity source – net metered• Water-to-water ground source heat pump

(GSHP)• Earth connection through standing column

well – same well as for water• Radiant heat tubing in thin slab on main

floor (Knight in occupied basement slab also)

The Houses -- Mechanicals

Why Bother?

• Can be powered with renewable energy• Owners desire for all renewable heat

with no combustion

Why Bother?

• “Renewable earth energy”?• “Free Energy”? From a recent

broadcast email:– Heat Your Home Without A

Furnace, Or Heating Bill

Why Bother?

• “Renewable earth energy”?• NO. Just a more efficient way to use

electricity.

Why Bother?

• Energy Cost Savings?

Fuel Cost/unitSystem

Efficiency$/MMBtu delivered

Oil, gal. $3.00 85% $26Propane, gal. $3.50 85% $45

Wood pellets, ton $190 85% $14Cord Wood $180 60% $14

Electricity, kWh $0.15 100% $44Electricity, kWh $0.15 250% $18

Data Summary

Measured:• BTU meter on output of GSHP• kWh meter on input to entire GSHP

system– Heat pump – Well pump– Circulators– Controls (VFD, Tekmar controller, GSHP,

thermostats, dump valve, transformers)

Data Summary – input/source side

COP Comparison at 97F - 107F Entering Water Temp

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Pill Knight StoneCOP

Manufacturer Unit COPMeasured Unit COPSystem COP

Data Summary – input/source sideCOP at 97F - 107F Entering Water Temp

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Pill Knight Stone AverageCOP

Manufacturer Unit COPMeasured Unit COPSystem COP

System COP – input/load sideSystem COP

0

0.5

1

1.5

2

2.5

3

3.5

Nov Dec Jan

CO

P

Stone

Pill

Knight

What makes me nervous?• Dearth of data --

Inflated claims?• Electronics – need

surge protection• Requires engineering• Industry not mature –

interactions of trades • Complexity -

mysterious glitches

What makes me nervous

• Installations in high load houses• Utility peak electric load implications• Water-to-air systems

– high volume/low temperature air– back-up use – resistance heating– retrofit situations

What makes me happy

• Systems working in five houses in Vermont, running on partial or all renewable energy!

Ground Source Heat Pumps –Design for Performance

• Part II – Details of systems design and data collected

Design for Performance –Devil is in the Details

• Low water temperature delivered from GSHP – 120F to 130F (?)

• Design houses for lower water temp: These super-insulated houses designed for 100F peak temp water in radiant slab -- increases COP of heat pump.

Design for Performance –Devil is in the Details

• Well water temperatures – mid to low 40’s F in Vermont

• High source and load flows required with low source and “high” load temperatures

Design for Performance –Devil is in the Details

• Watts everywhere!– Well pump – 1500 watts full speed/ 500 to

600+ at reduced speed with VFD

Well pump VFD test 23-Jan-0715 gpm Sta-Rite pump with 1 HP Franklin 3-phase motor, Hitachi L-200 VFD

Speed flow input power pressure output power efficiency input wattsHz gpm watts psi watts wire to water per gpm

30 8.0 321 16 56 17% 4030 8.5 320 18 66 21% 3830 8.3 309 20 72 23% 3730 8.3 302 20 72 24% 3634 10.4 309 20 90 29% 30 sweet spot36 11.5 426 20 100 23% 3738 12.3 477 20 106 22% 39 actual40 13.0 527 20 113 21% 4152 7.5 871 86 280 32% 11660 17.2 1347 60 448 33% 7860 14.3 1364 86 534 39% 95 [1]

Design for Performance –Devil is in the Details

Watts everywhere!• Circulators – 200 watts, even with care with

pressure drops:– Piping, sizes and elbows, widgets– heat pump and tank Hx’s (3)– Tank inlets and outlets

Water Furnace EW030H/R performance data8 gpm on well side Load 8 gpm

Well pump Load circ Total SystemELT EST, F LLT COP kW LST kW kW kW COP

80 30 87 4.1 2.1 24interpolated 45 89 5.1 2.1 38 0.50 0.3 2.9 3.6

50 90 5.4 2.1 42100 30 107 3.2 2.6 25

interpolated 45 109 3.9 2.6 39 0.50 0.3 3.4 3.050 109 4.2 2.6 43

120 30 127 2.5 3.3 26interpolated 45 129 3.0 3.3 40 0.50 0.3 4.1 2.4

50 129 3.2 3.3 44

Knight House -- One-Time Test -- COP vs Entering Load Temp

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

70 80 90 100 110 120Deg F Entering Load Temp

CO

PManufacturer COPUnit COPSystem COP

Atwood-Stone House - COP vs Entering Load Temp

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

80 90 100 110 120Deg F

CO

P

Manufacturer COPUnit COPSystem COP

• Reduce house loads significantly!

• Design for low output temperatures

• Lower pump energy by reducing friction

• Lower other electric “parasitic” energy

• Use realistic COP’s in design

• Simpler = more reliable!

How to make GSHP houses work?

• Extremely low load houses

• Run on renewables!

How to make GSHP houses work for all of us?