Air to Water Heat Pump Energy Savings and Payback Period in North America
Air to Water Heat Pumps Savings and Paybacks
This Blog analyses DC Inverter Air to Water Heat Pump Performance, Cost and Payback Period in various North American Cities across Canada and the United States.
What is Air to Water Heat Pump?
Air to Water Heat Pump is a machine that draws heat from one place (called heat source) and reject the drawn heat to another place (called heat sink). Unlike
conventional air to air heat pump, where generated thermal energy is used to cool/heat air, Air to Water Heat Pumps use generated thermal energy to cool/heat
water or water/glycol fluid mixture. Our air to water heat pumps are equipped with DC inverter Compressor and EVI (Enhanced vapor injection) technology, which
allows them to delivery higher temperature fluid in much colder outdoor temperatures when compared to conventional two stages or DC inverter only (without EVI)
Heat Pumps.
DC inverter compressors are variable speed compressors powered by direct current inverters. Speed is modulated via an external variable-frequency drive to
control the speed of the compressor. The refrigerant flow rate is changed by the change in the speed of compressor. The turndown ratio depends on the system
configuration and manufacturer. It modulates from 15 or 25% up to 100% at full capacity. This means that heat pump operating with a DC inverter compressor can
matches its capacity to demand by simply modulating its compressor speed. Unlike conventional one or two stages compressors, Heat Pumps equipped with
a DC inverter compressor do not cycle ON and OFF more frequently, they run most of the time at lower speeds.
As shown in the above schematic, the liquid out of the condenser is separated into two parts. A smaller part of the liquid, i, is expanded through an additional
expansion valve, and then directed (or flows) into a counter-flow plate heat exchanger, HX. The main part of the liquid out of the condenser, m, is then cooled down
through the economizer while evaporating and superheating the injection mass flow. This additional plate heat exchanger, more generally called economizer, acts
therefore as a sub cooler for the main mass flow m and as an evaporator for the injection mass flow. Superheated vapor is then injected into the intermediate vapor
injection port in the scroll compressor.
The additional subcooling increases the evaporator capacity by reducing the temperature of the liquid from TLI to TLO, thus reducing its enthalpy. The additional
condenser mass flow, i, increases the heating capacity by the same amount.
Efficiency with vapor injection scroll compressor cycle is higher than that of a conventional single stage scroll delivering the same capacity because the added
capacity is achieved with proportionally less power. The injection mass flow created in the subcooling process is compressed only from the higher inter-stage
pressure rather than from the lower suction pressure.
The additional Sub-cooling effect of EVI configuration allows heat pump to draw heat from the outdoor at lower outdoor temperatures. That could explain why DC
inverter (Non EVI) Heat Pumps operate between -20⁰C and 45⁰C (Outdoor BD Temperatures) while DC Inverter EVI Heat Pumps operate between -25⁰C and
45⁰C (Outdoor BD Temperatures).
Why Air to Water Heat Pumps are becoming so popular?
Canadian/US Building Codes are becoming more demanding in terms of energy efficiency for both residential and commercial buildings. Canadian Federal
Government is aiming to gradually increase the energy efficiency standard for both existing and new constructions by requiring that every new home in Canada be
Net Zero Ready by 2025 and completely Net Zero by 2030.
Getting Gradually to the Net Zero Energy will have to make sense, not only from an environmental point of view but from a financial and social point of view too.
Even though renewable energies’ prices are going down and efficiency is going up, they are still not affordable for a normal middle-class North American Household when adding the cost of labor to the cost of materials. Also, labor cost increases twofold when retrofitting an existing home with one or a combination of several
renewable energy sources (such as solar, geothermal, etc.…).
Before the emergence of Air to Water Heat Pumps, Canadian/US homes and business owners who wished to heat/cool their properties with hydronic systems had
only two choices: either Conventional Electric/Gas/Propane/Wood boilers which are affordable but extremely environmentally unfriendly or Geothermal Heat Pumps
which are extremely expensive and environmentally friendly.
Air to Water Heat Pumps combine affordability and energy efficiency and do make a great sense when comparing budgets for conventional Boiler based scenario,
Air to Water Heat Pump Scenario and Geothermal Scenario.
Geothermal Heat Pump, for a regular Canadian/US home, has an annual COP (Coefficient of Performance) of around 3. A similar capacity Air to Water Heat pump
has an annual COP of 2.2-2.7 for a much lower cost. In General, Air to Water Heat pumps are 20-30% less efficient that their geothermal peers but they are 60%
cheaper.
Energy Simulation Scenario
For the sake of this blog, we will simulate the performance of a Split Air to Water Heat Pump HSS060V2LS for a 2000 square foot cottage in multiple North American Cities spanning from Halifax East to Vancouver and Seattle West.
Case Analysis Assumptions:
- House is a Cottage with a basement having a nominal heating load of 10 KW (34 MBH).
- Thermal Properties are as per minimum Buildings Code Requirements (R24 for Wall, R40 for Roof, R10 for Slab, Double Glazing, Windows Wall Ratio 20%).
- Four persons are living in the house: two adults and two kids (for domesctic hot water DHW demand calculation)
- Each Person consumes 75L (20 US Gallons) of DHW daily.
- House is heated via a hydronic infloor heat - infloor loops are located in the basement and in the ground floor.
- Upper floor is heated and cooled by individual Hydronic Fan Coil Units (one in every room).
- Used ATW heat pump has a DC inverter compressor and EVI technology.
- Heat Pump is used to Pre-Heat DHW with Space Heating and Cooling as a priority.
- Back up heater is an electric boiler with 100% thermal efficiency and modulating (SCR) heating elements. Boiler authorisation to work is given by the Heat Pump.
- Three way valve switching between DHW tank and Space Heating/Cooling tank is Floating Type - ON/OFF - 230V Power Supplied.
- Circulation Pump dedicated for ATW Heat Pump is a variable speed pump with ECM motor and speed is controller by a PWM signal.
- Both thre way valve and pump operation and control is interlocked with the heat pump.
Piping Schematics on the right shows a split air to water heat pump, which used water as heat transfer fluid (HTF).
Hydro Solar Monoblock and Split ATW heat pumps have similar perfromance for similar fluid flows.
Schematics show a dual compartment tank, however the same configuration can be done with two separate individual tanks: One dedicated for DHW pre-heating and another tank for space heating/cooling.
When local regulations allow for combined DHW and space heating system, pre-heating DHW directly through the DHW tank shall be favored since it allows for a larger pre-heating volume. When Combined System is not allowed, pre-heating DHW shall be done via the tank indirect coil.
Always use back up heat for both DHW and Space Heating application.
Energy Simulation Results
Summary of Energy Simulation for Various North American Cities have been tabulated in 2 separate tables: one for Canadian Cities and another one for US cities. Utility rates used to calculate savings amount in CAD or USD were taken out from utility compagnies websites at the time of writing this blog. We used a 5 Tons Air to Water Split Heat Pump HSS060V2LS with Heating Performance as shown in the below table:
Canadian Cities Simulation Results:
| Annual Simulation Result Parameters | Brampton (ON) | Burlington (ON) | Burnaby (BC) | Calgary (AB) | Edmonton (AB) | Halifax (NS) | Kelowna (BC) | Vancouver (BC) | Montreal (QC) |
|---|---|---|---|---|---|---|---|---|---|
| Building Envelope Heating Demand (KWh) | 21 000 | 21 248 | 21 412 | 21 251 | 21 192 | 21 260 | 21 362 | 21 423 | 21 169 |
| Domestic Hot Water Heating Demand (KWh) | 5 262 | 5 061 | 4 912 | 5 572 | 5 655 | 5 332 | 5 150 | 4 905 | 5 297 |
| Total Hydronic Heating Demand (KWh) | 26 348 | 26 309 | 26 324 | 26 823 | 26 847 | 26 592 | 26 512 | 26 328 | 26 466 |
| Base Scenario (Electric Boiler) Heating Consumption (KWh) | 26 348 | 26 309 | 26 324 | 26 823 | 26 847 | 26 592 | 26 512 | 26 328 | 26 466 |
| Air to Water Sceanrio (ATW HP + Electric Boiler as Backup) Heating Consumption (KWh) | 9 661 | 9 486 | 8 811 | 10 715 | 11 090 | 9 703 | 9 545 | 8 749 | 10 278 |
| Annual Savings (KWh) | 16 687 | 16 816 | 17 513 | 16 108 | 15 757 | 16 889 | 16 967 | 17 579 | 16 188 |
| Electricity Price (CAD/KWh) | 0.135 | 0.135 | 0.0959 | 0.135 | 0.135 | 0.1635 | 0.0959 | 0.0959 | 0.0825 |
| Annual Savings (CAD) | 2,252.74$ | 2,270.16$ | 1,679.5$ | 2,174.5$ | 2,127.2$ | 2,761.3$ | 1,627.1$ | 1,685.8$ | 1,335.5$ |
| Annual Saving (%) | 63.3% | 63.9% | 66.52% | 60% | 58.7% | 63.5% | 63.9% | 66.7% | 61.1% |
| Annual Coefficient of Performance (COP) | 2.72 | 2.77 | 2.98 | 2.5 | 2.42 | 2.74 | 2.78 | 3.0 | 2.57 |
| ATW Heat Pump Kit Price (CAD - Before Shipping and Taxes) | 14,702$ | 14,702$ | 14,702$ | 14,702$ | 14,702$ | 14,702$ | 14,702$ | 14,702$ | 14,702$ |
| PayBack Period (Years) | 6.52 | 6.47 | 8.75 | 6.76 | 6.91 | 5.32 | 9.03 | 8.72 | 11.0 |
US Cities Simulation Results
| Annual Simulation Result Parameters | NY City (NY) | Burlington (VT) | Newark (NJ) | Manchester (NH) | Philadelphia (PA) | Chicago (IL) | Kansas City (M0) | Cody (WY) | Seattle (WA) |
|---|---|---|---|---|---|---|---|---|---|
| Building Envelope Heating Demand (KWh) | 21 297 | 21 205 | 21 197 | 21 199 | 21 206 | 21 209 | 21 134 | 21 253 | 21 426 |
| Domestic Hot Water Heating Demand (KWh) | 5 755 | 5 156 | 4 600 | 4 599 | 4 517 | 4 840 | 4 520 | 5 217 | 4 739 |
| Total Hydronic Heating Demand (KWh) | 27 052 | 26 361 | 25 797 | 25 798 | 25 723 | 26 049 | 25 654 | 26 470 | 26 165 |
| Base Scenario (Electric Boiler) Heating Consumption (KWh) | 27 052 | 26 361 | 25 797 | 25 798 | 25 723 | 26 049 | 25 654 | 26 470 | 26 165 |
| Air to Water Sceanrio (ATW HP + Electric Boiler as Backup) Heating Consumption (KWh) | 10 564 | 9 691 | 9 078 | 9 049 | 8 992 | 9 488 | 9 243 | 9 984 | 8 614 |
| Annual Savings (KWh) | 16 488 | 16 670 | 16 719 | 16 479 | 16 731 | 16 651 | 16 411 | 16 486 | 17 551 |
| Electricity Price (USD/KWh) | 0.21 | 0.1995 | 0.1625 | 0.3066 | 0.147 | 0.1727 | 0.15 | 0.1365 | 0.13 |
| Annual Savings (USD) | 3,462.5$ | 3,325.6$ | 2,716.8$ | 5,135.2$ | 2,459.4$ | 2,860.1$ | 2,461.6$ | 2,250.3$ | 2,281.6$ |
| Annual Saving (%) | 60.9% | 63.3% | 64.8% | 63.8% | 65.04% | 63.9% | 63.9% | 62.2% | 67% |
| Annual Coefficient of Performance (COP) | 2.56 | 2.72 | 2.84 | 2.85 | 2.86 | 2.74 | 2.77 | 2.65 | 3.03 |
| ATW Heat Pump Kit Price (USD - Before Shipping and Taxes) | 13,922.3$ | 13,922.3$ | 13,922.3$ | 13,922.3$ | 13,922.3$ | 13,922.3$ | 13,922.3$ | 13,922.3$ | 13,922.3$ |
| PayBack Period (Years) | 4.02 | 4.18 | 5.12 | 2.71 | 5.66 | 4.86 | 5.65 | 6.18 | 6.1 |
Conclusion:
When Air to Water Heat Pumps are used for space heating and DHW pre-heating as well, they can reduce Hydronic Heating demand (DHW and Space Heating Combined) by around 60%. Also Annual Heating COP is between 2.5 and 3 depending on weather conditions. Payback period is less in the US than in Canada due to multiple factors such as USD/CAD exchange rates, higher energy prices and availability of energy sources.
