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 Heat Pump Inspection, Diagnosis, Inspection, Repair Guide
- HEAT PUMPS - Heat pump system inspection, diagnosis, repair articles for home owners and building inspectors
- How do heat pumps work?
- How the Heat Pump Works When in Cooling Mode = Summer Mode
- How a Heat Pump Operates to Extract Heat from Outdoor Air When in Heating Mode = Winter Mode
- Troubleshooting backup heat problems on heat pump systems that provide both air conditioning and heating
- How to determine heat pump capacity
- What is the COP or Coefficient of Performance of Heat Pumps? What is the COP balance point for heat pump designs?
- Heat pump system components and parts and a comparison of air, water, and ground source heat pump designs
- How does a Triple Split System Heat Pump System operate?
- How does a Bi-Valent Heat Pump System Work?
- DEFECTS LIST - HEAT PUMP - separate article
- HEAT PUMP COP - separate article
- HEAT PUMPS, GROUNDWATER - separate article
- HEAT PUMP STRATEGY - Indoors? - separate article
- HEAT PUMP Thermostats - Outdoors - separate article
- Questions & Answers about how to diagnose & repair residential heat pump systems
- References
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InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
Heat pump system inspection, basics of operation, troubleshooting & repair guide. This article series answers most questions about heat pump system troubleshooting, inspection, diagnosis and repair. We explain how heat pumps work to provide cooling in hot weather and heating in cool or cold weather. We explain the concept of coefficient of performance or COP, and how the COP balance point determines how much use can be made of a heat pump in different climates.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Heat Pump System Inspection, Diagnosis, Repair - List of Articles
This article describes how to inspect residential heat pump systems (combination heating and cooling systems) to inform home buyers, owners, and
home inspectors of common heat pump system defects.
The articles at this website describe the basic components of a heat pump system, how heat pumps are inspected, diagnosed, and repaired, and we discuss how to estimate the rated heating and cooling capacity of a heat pump system by examining various data tags and components.
The limitations of visual inspection of HVAC systems are described.
Heat Pump Operating Principles
The schematic of a heat pump system shown above and the sketch at left are compliments of Carson Dunlop Associates.
A "heat pump" is an air conditioning system that can work in either of two directions.
During the cooling season the heat pump moves heat from inside the building to outdoors by removing heat from indoor air - by blowing indoor air across the evaporating or cooling coil.
During the heating season the same equipment reverses the direction of its operation, scavenging heat from outdoor air and moving it into the building - by blowing indoor air across a warmed condensing coil, and by blowing outdoor air across the outdoor coil.
Controls in the heat pump reverse the operation and flow of the refrigerant in order to change the direction of heat movement between the indoor and outdoor areas.
Since most components of a heat pump system are identical with those of central air conditioning systems, readers should also be sure to review our air conditioning system inspection, diagnosis, and repair articles.
Below we expand the explanation of how a heat pump works in summer - cooling mode and how a heat pump works in winter - heating mode. |
How the Heat Pump Works When in Cooling Mode = Summer Mode
Below we illustrate the heat pump operation when the equipment is in heating mode.
In cooling mode the heat pump works like a conventional air conditioner. The indoor cooling coil expands liquid refrigerant into a gas form, cooling the coil. Indoor air is cooled by being blown across the indoor cooling coil (left side of the Carson Dunlop Associates' image).
Outside the refrigerant gas is compressed to high pressure high temperature gas, then sent through the outdoor condensing coil where outdoor air blown across the condensing coil condenses the refrigerant back to a liquid for its return to the indoor components.
Even though the outdoor air may be hot during the cooling season, it is at a lower temperature than the outdoor condensing coil - so the system works to transfer heat from indoors to outside.
See the next two illustrations for more detail about this process when we switch to heating mode. |
How a Heat Pump Operates to Extract Heat from Outdoor Air When in Heating Mode = Winter Mode
Illustrations below provided by Carson Dunlop Associates.
Different or Additional Controls Required for a Heat Pump vs an Air Conditioner: Refrigerant Expansion Devices
We have said often that a heat pump is pretty much like an air conditioner, with a few control differences to allow the system to reverse its direction of heat movement between the indoor and outdoor areas.
In an air conditioner the outdoor coil is used only to cool and condense high temperature high pressure refrigerant gas back to a liquid refrigerant, and the indoor coil is used only to expand the liquid refrigerant to a gas (through an expansion device such as a Thermostatic Expansion Valve (TEV) or a capillary tube (Cap Tube).
But because a heat pump has to be able to work in both directions, its indoor and outdoor coil have to be able to exchange roles. To accomplish this the heat pump will need two refrigerant metering and expansion devices, one at each coil. Only one of the expansion devices is operating at a given time - depending on whether the equipment is operating in a heating or in a cooling mode.
Illustration provided by Carson Dunlop Associates. |
Reversing Valve and Defrost Cycle Operation Procedure for Heat Pumps
In addition to the two expansion devices, the system may make use of a reversing valve that changes the direction of flow of refrigerant gas and liquid in the system.
An additional set of controls for operation the refrigerant reversing valve and the operation of the defrost cycle for a heat pump are illustrated at left. During a defrost cycle
- The reversing valve changes direction of the refrigerant flow to send warmed refrigerant "freon" to the outdoor coil in order to melt ice that may have formed there.
- During the defrost cycle the outdoor fan stops - we want to stop moving outdoor air across the outdoor coil in order to allow the warm refrigerant to warm the coil.
- If the system includes electric heating elements, one stage of the electric BACKUP HEAT for HEAT PUMPS may be activated in the blower compartment to warm air coming off of the blower. If the system does not include electric backup heaters, the indoor air handler blower will stop during the defrost cycle so that we don't' blow wrong-temperature air into the occupied space.
Illustration provided by Carson Dunlop Associates. |
What is an "All Electric" Heat Pump System? - Compared with Gas or Oil Backup Heat
The operation of the outdoor compressor/condenser unit and the indoor air handler blower assembly unit is normally run by electrical power.
When the back-up heat for a heat pump operated building is also all electric we refer to the installation as an all-electric heat pump installation. All electric heat pump systems are suitable where electrical energy costs are low or where the number of heating degree days in the local climate is modest.
See BACKUP HEAT for HEAT PUMPS for a discussion of how a heat pump electric backup heat system is tested.
For locations subject to very cold winter weather with many heating days during which outdoor temperatures are below the balance point for heat pump operation, building owners typically use a fossil-fuel backup heat such as natural gas, propane, or heating oil, and may heat by an integrated furnace or by a separate heating system.
Illustration provided by Carson Dunlop Associates. |
How does a Water Source Heat Pump System Work?
The operation of a water source heat pump system depends on accomplishing its temperature change by using water from a well, or more generally from a pair of wells.
Some water source heat pumps use one or a cascade of water storage tanks. In a water storage tank design, well water is pumped into the storage tank and the heat pump continues to pump heat into the water or take heat from the water (depending on summer or winter mode operation) until the temperature of the water no longer permits an efficient energy exchange.
At that point the energy exchange available in the tank of water has been exhausted - the tank is pumped back into a discharge well, or in some older designs, into another destination.
More details about measuring the efficiency or COP and EER of ground water heat pumps are found at HEAT PUMPS, GROUNDWATER
Illustration provided by Carson Dunlop Associates. |
How does a Ground Source Heat Pump System Work?
For a simple understanding of all heat pump systems, air, water, or ground-sourced, it helps to understand that we are always moving heat back and forth between the heat pump and the air, water or ground. The differences are in the medium of exchange, not in the basic system operation and controls.
The operation of a ground sourced heat pump system is described by the illustration at left.
Unlike the water based heat pump operation, the ground sourced heat pump system uses a loop of pipes buried in soil to exchange heat with the ground; a separate tank system or discharge well system is not required.
Illustration provided by Carson Dunlop Associates. |
Sketch of a Triple Split System Heat Pump System
The sketch at left illustrates how a triple split system heat pump is organized.
The compressor motor is installed and located as a separate component inside the building while the other system components (outdoor coil and indoor coil) remain in their traditional locations.
Illustration provided by Carson Dunlop Associates. |
How does a Bi-Valent Heat Pump System Work? Three Operating Modes all using the outdoor coil
The operation of a bivalent heat pump is not as confusing or intimidating as the name might sound.
A bi-valent heat pump installation adds this term to handle three different heat pump operating conditions:
- Cooling mold - the system works as the heat pumps described earlier in this article
- Heating mode 1. In moderately-cool outdoor temperature conditions during which the outdoor temperature does not drop below a preset level, typically 38 degF. the heat pump provides heat to the building without resorting to a backup heat system.
- Heating mode 2. In colder outdoor conditions when the outside temperature is below the set point (we're using 38 F.) an auxiliary or backup heating system (such as LP or natural gas burners) operates to warm the outdoor coil that in turn is used to deliver heat to the occupied space.
Illustration provided by Carson Dunlop Associates. |
What is the COP or Coefficient of Performance of Heat Pumps?
The COP or coefficient of performance describes the ability of a heat pump to extract heat from outdoor air down to some low temperature, typically 25 degF. for modern equipment. The COP determines how effective a heat pump can be at providing heat during cool or cold weather.
Details including a definition of COP, an explanation of the heat pump balance point, and how to calculate heat pump operating cost more accurately by considering degree days are at HEAT PUMP COP - Definition, sources of variation in heat pump operating efficiency & cost
Heat Pump operating cost variables & COP Calculations
Where a heat pump is used to provide part of the building's heat requirements, the efficiency of the air-to-air heat pump will be less at lower temperatures. Spies (1971, 1977) [2] notes that heat pump efficiency when outdoorr air is warm is quite different from at cold temperatures, making its use of electricity more complex.
The coefficient of utilization may be as high as 3.0, falling to 1.0 as outdoor temperature approaches 10 degF. In 1971 when Spies wrote that note for the Small Homes Council, few heat pumps worked at temperatures that low, Also that this was in 1971, newer equipment is capable of efficient heat extraction from colder air. Spies provided a calculation to transfer heat pump efficiency or COP into electrical costs when comparing heating fuel type cost alternatives:
Table of Electricity Cost Divisors for Heat Pump Operating Cost vs Degree Days - Outdoor Temperature |
| Degree Days for Your Location |
Electricity Price Divisor |
Comments |
| 8000 degree-day heating season |
1.4 |
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| 6000 degree-day heating season |
1.7 |
|
| 4000 degree-day heating season |
2.2 |
|
Notes:
Henry Spies, "Fuels & Burners", Small Homes Council - Building Research Council Circular Series #G3.5, 1971. 1977 |
Example: If you live in a climate in which the average number of degree days in the heating season is 4000, then to compare heat pump operating costs (using electricity) to other fuels and heating methods,
divide your current electricity cost (say 5 cents per kwh) by 2.2.
5 / 2.2 = 2.27 cents / kwh
List of Heat Pump Inspection, Diagnosis, & Repair Articles
Also see AIR CONDITIONING & HEAT PUMP SYSTEMS where we introduce and illustrate the basic components of air conditioners and heat pumps.
Heat Pump Stopped Heating or Cooling - Diagnostic Guide
If your heat pump system has lost its cooling capacity or won't start select one or more of the diagnostic articles listed below.
- A/C REFRIGERANT LEAK DETECTION: how to use a TIF5000 to detect air conditioning refrigerant gas leak
- A/C DIAGNOSTIC FAQs: air conditioning system diagnostic FAQs: Q&A about air conditioner repair - a detailed air conditioning system diagnostic checklist
- AIR HANDLER UNIT: problems with the air handler, air filters, and the cooling coil itself
- BACKUP HEAT: on heat pumps, types of backup heat; problems with backup heat; begin here if your heat pump is not providing enough heat or if your air conditioning system provides heat when it should be providing cooling.
- COMPRESSOR CONDENSER: problems with air conditioner compressor/condenser units including noises and compressor hard-starting repairs
- A/C - HEAT PUMP CONTROLS & SWITCHES: air conditioner controls and switches - begin here if your A/C won't start. Here's an important tip: most refrigeration problems, in air conditioners, refrigerators, or freezers, are electrical, not mechanical. In air conditioning school, we used to drive out and collect abandoned refrigerators that people were tossing out during our community's spring cleanup week. Taking these appliances back into the shop we found that almost always the problem that had caused the owner to dispose of their air conditioner or freezer was in an electrical connection or electrical control. So it's worth checking out switches and controls on an air conditioner before replacing more costly components.
- Dehumidification Problems - Air conditioner cools but does not dehumidify
- DUCT SYSTEM DEFECTS: problems with the air duct system, air filters, supply registers, return air registers
- Fire dampers, and Heating and Cooling Air Duct Controls such as manual and automatic duct dampers, zone dampers, and fire dampers are discussed and distinguished at DRAFT REGULATORS - barometric damper
- LOST COOLING CAPACITY: what to do when not enough cool air comes out of the system - the articles in this series also assist in diagnosis of lost heating capacity for heat pump systems.
- OPERATING DEFECTS: major air conditioning problem symptoms and how to get the air conditioning system working again,e.g. compressor or fan noises, failure to start, and inadequate cool air volume
- ZONE DAMPER CONTROLS . discusses manual and automatic air duct zone controls
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
Click to Show or Hide Citations & References
- Thanks to AMark Cramer, Tampa Florida, for assistance in technical review of the "Critical Defects"
section and for the photograph of the deteriorating gray Owens Corning flex duct in a hot attic. Mr. Cramer is a Florida home inspector and
home inspection educator.
- [2] Henry Spies, "Fuels & Burners", Small Homes Council - Building Research Council Circular Series #G3.5, 1971. 1977 [copy on file as PDF]
- Thanks to Neal Renn who described diagnosing the problem of a heat pump that "only gets backup heat and no cooling" to describe the problem of a heat pump that insists on turning on backup heat when it is not needed.
 Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.
Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
- The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones.
- Thanks also to Alan Carson, Carson Dunlop, Associates, Toronto, for technical critique and for providing a copy of Carson Dunlop Weldon & Associates Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment ($69.00 U.S.).
- Geothermal HVAC, [Amazon.com] Jay Egg & Brian Howard, McGraw-Hill Professional; ISBN-10: 0071746102, ISBN-13: 978-0071746106, quoting:
This definitive guide covers commercial and residential geothermal heating, ventilation, and air conditioning technologies and explains how to take advantage of their money- and energy-saving features. Geothermal HVAC: Green Heating and Cooling reviews the array of choices currently available, offers market values for systems based on varying options and conditions, and describes how to pair the best systems for each application and budget. Whether you're a contractor or a consumer, you'll find out what you need to know to implement a geothermal HVAC system in a retrofit or new construction project, and start benefiting from this sustainable, affordable technology.
- Geothermal Heat Pumps: A Guide for Planning and Installing, [Amazon.com], Karl Ochsner, Robin Curtis, Earthscan Publications Ltd. (December 2007), ISBN-10: 1844074064, ISBN-13: 978-1844074068quoting:
Geothermal Heat Pumps is the most comprehensive guide to the selection, design and installation of geothermal heat pumps available. This leading manual presents the most recent information and market developments in order to put any installer, engineer or architect in the position to design, select and install a domestic geothermal heat pump system. Internationally respected expert Karl Ochsner presents the reasons to use heat pumps, introduces basic theory and reviews the wide variety of available heat pump models. Expertly reviewed and adapted for the most geographically broad application possible, the book offers the reader valuable tips for planning and system control using data, graphics and tables from a growing and innovative market.
- Residential Geothermal Systems: Heating And Cooling Using The Ground Below, [Amazon.com], John Stojanowski, Pangea Publications LLC (March 17, 2010)
ISBN-10: 0981922112, ISBN-13: 978-0981922119. Quoting from Amazon.com reviews:
Readers will learn how heat pumps are able to extract heat from relatively low temperature water circulating in ground loops and raise it to a temperature high enough to heat a home. They will also learn how to estimate the size of the heat pump required and the ground loop size as well for straight 2-pipe, 4-pipe, 6-pipe and Slinky loop configurations. This is important in order to verify that the installer correctly sizes the system. Both horizontal and vertical loop systems, for GX and DX, are covered.
Some of the technical issues that are addressed include: Loop water flow rates and Reynolds Number, heat of extraction/rejection, heating capacity, de-superheater setup, open-loop/closed-loop, SCW, pond loops, DX, Manual-J, COP. The final chapter consists of a set of flowcharts guiding the homeowner to ask the pertinent questions needed for a successful installation.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
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- Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
- Complete List of Air Conditioning & Heat Pump Design, Inspection, Repair Books at the InspectAPedia Bookstore.
- Modern Refrigeration and Air Conditioning, A. D. Althouse, C.H. Turnquist, A. Bracciano, Goodheart-Willcox Co., 1982
- Principles of Refrigeration, R. Warren Marsh, C. Thomas Olivo, Delmar Publishers, 1979
- "Air Conditioning & Refrigeration I & II", BOCES Education, Warren Hilliard (instructor), Poughkeepsie, New York, May - July 1982, [classroom notes from air conditioning and refrigeration maintenance and repair course attended by the website author]
- Refrigeration and Air Conditioning Technology, 5th Ed., William C. Whitman, William M. Johnson, John Tomczyk, Cengage Learning, 2005, ISBN 1401837654, 9781401837655 1324 pages
 Air Conditioning SEER - New DOE Air Conditioner and Heat Pump Efficiency Standard- Asbestos HVAC Ducts and Flues field identification photos and guide
- Fiberglass: Indoor Air Quality Investigations: Fiberglass in Indoor Air, HVAC ducts, and Building Insulation
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