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How Low Can Nordic Heat Pumps Go?

By Nordic

January 23, 2017

Products

heat pump effective temperature
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Air source heat pumps have long had a reputation for being an excellent alternative to expensive heating options like oil or electric baseboards, but many brands fall short when it comes to performing well in colder temperatures. That has changed with the introduction of cold weather heat pumps, which are heat pumps that are specifically designed for cold weather, like our air to water heat pump.

But what makes a heat pump suitable for cold weather? And what does that term mean anyway? Unfortunately, while many heat pumps are advertised as cold climate heat pumps, few are equipped with features to make them perform better than conventional heat pumps when the temperatures drop, and few manufacturers list the heat pump’s effective temperature range.

We’re going to change that today by walking you through the unique features that make our air source heat pumps perform better in cold weather, and show you the actual efficiencies our heat pumps achieve at different outdoor temperatures.

Inspired Design

When it comes to the overall layout of the machine, we drew on our experience and knowledge in the geothermal heat pump field to inform the design of the air source heat pumps. Geothermal heat pumps are the ultimate cold weather heat pumps (which we’ll explain further below), partially because the heat pump is located inside the home in a dry, conditioned space. Putting the heat pump indoors reduces the wear and tear on the main components of the heat pump and boosts the longevity of the machine.

That’s why Nordic air source heat pumps have the majority of their components located inside, where they are out of the weather and safe from mother nature. The only parts of the heat pump that are located outdoors are:

  • the heat exchanger
  • the fan to move air across the heat exchanger
  • the electronic expansion valve

Intelligent Defrost Logic

When a heat pump is operating in heating mode, frost accumulates on the outdoor heat exchanger. This is a naturally occurring phenomenon, but the frost acts as an insulator and reduces the heat pump’s efficiency by reducing the heat transfer from the outdoor air to the coil. To eliminate the frost, the heat pump will go through a defrost cycle where it switches into cooling mode. In cooling mode, it is moving heat from the home into the outdoor air. The heat pump melts the frost, switches back into heating mode and continues heating the home. Most air source heat pumps will defrost on a timer, which can lead to partial defrosts (where part of the coil doesn’t fully defrost) or too many unnecessary defrosts, which is inefficient.

All Nordic air source heat pumps are equipped with intelligent defrost logic. Intelligent defrost logic is a program run by the heat pump’s control board that uses several inputs to determine exactly when the heat pump needs to run a defrost cycle on the outside air coil. Because the intelligent defrost logic ensures the heat pump only defrosts when necessary, this program automatically maximizes the heat pump’s efficiency and minimizes operating costs.

Smart Fan Operation

One issue frequently mentioned by homeowners with heat pumps that aren’t designed for cold weather is that snow will often clog up the outdoor unit, preventing it from operating. With a Nordic air source heat pump, when the outdoor temperature drops to the point where snow is possible, an outdoor temperature sensor sends a signal to the control board to turn the outdoor fan on at a low speed, even if the heat pump isn’t running. This low-speed fan operation keeps snow from building up inside the unit.

We Added a Leg Kit and Remove a Drain Pan

The outdoor portion of the heat pump has two other features that make it uniquely designed for cold weather operation. First, there is no drain pan on the bottom of the heat pump, in fact, there is no bottom at all. This is so condensation doesn’t drip off the heat exchanger and freeze, possibly building up in the pan and/or breaking the coil. Instead, moisture will drip off directly onto the ground. The outdoor part of the heat pump also comes with an optional leg kit to lift it up and away from the snow so that it won’t get buried in a snow drift if mother nature decides to come calling.

Air Source & Geothermal Heat Pump Effective Temperature Range

While our air source heat pumps will operate down to -4°F (-20°C), the colder the outdoor air, the harder the heat pump will have to work to produce heat for your home. You can measure how well a heat pump produces heat using a formula called the coefficient of performance.

The coefficient of performance essentially measures how much energy output is produced for a specific energy input and expresses it as a number. For example, if a heat pump requires 1 watt of energy in to produce 4 watts of energy out, it would have a COP or 4/1 or 4.0. The extra three watts of energy come from either the air (for air source heat pumps) or the earth (for geothermal heat pumps). You can find more detailed explanation of heat pump COP at the link.

Geothermal heat pumps have a steady COP because their heat source (the ground) never fluctuates in temperature. The ground always maintains a constant temperature, no matter how cold or hot it is outside.  This stable heat source makes geothermal heat pumps the ultimate cold weather heat pump, but air source heat pumps can still get the job done. Air source heat pumps have a fluctuating COP because their heat source (the air) fluctuates as the season changes.

To help take some of the mystery out of these fluctuating COPs and give you a sense of the heat pump effective temperature range and efficiencies at freezing outdoor temperatures, we’ve mapped how our heat pumps perform at different temperatures.

heat pump effective temperature range

The data above was taken from an ATW-65 and the equivalent geothermal heat pump (W-65) on both an open and closed geothermal ground loop.

As you can see, the warmer the outdoor air, the better the air source heat pump performs. As the outdoor air temperature drops, the heat pump needs to work harder, so it becomes less efficient. The COP continues to drop until we reach an outdoor temperature of -4°F (-20°C). -4°F is the lower limit of our air source heat pump effective temperature range. In temperatures lower than that the heat pump shuts down and electric backup heat takes over. The backup heat protects the compressor and preserves the longevity of the machine. The backup heat may also come on periodically in warmer temperatures if the heat pump alone cannot satisfy your home’s heat load. Electric backup heat has a COP of 1.0.

You’ll also notice that the geothermal heat pump lines are higher and remain constant. That’s because the ground does not fluctuate in temperature the way the outdoor air does, so a geothermal heat pump will never lose efficiency (except in extreme cases), and never needs backup heat. Air source heat pumps can be optimized to perform cold weather heating, but geothermal heat pumps will always be the ultimate cold weather heat pump.

Learn more about Nordic air source heat pumps by downloading our free Ebook: All About Air Source: How Innovative Air to Water Heat Pumps Differ From Geothermal.

Or

Find a Dealer for a customized quote!

Comments

  1. Reply

    Norm Noseworthy

    January 28, 2017

    We are just having a new Nordic heat system installed in a new house at 26 Bowater Blvd. in Pasadena Newfoundland by Unique Heating in Corner Brook. We are looking forward to the comfort and economics of the system. The system is taking along time to install should be up and running in a day or so.

  2. Reply

    Denis Arsenault

    February 01, 2017

    Hi , my name is Denis Arsenault , I don’t have a comment but more of a question , is it normal that the compressor keeps on running 24/7? It’s our first winter with a geothermal and we already had some problems with it , first 3 weeks getting a filter for it because our provider could not order the proper one . Then it got colder outside and the go thermal ran all day and night so we called our provider and thy came to see 2 times and thy sad that the sisttem was wired Wrong at the united and at the thermostat , so it appeared that it was wired Wrong since Aprill of 2016 . Do I need to concern my self with this problem any ferther ?

    • Jordann Brown

      February 03, 2017

      Hi Denis,
      Could you email us at info@nordicghp.com and we can help you with your questions? It would be helpful if you included your heat pump’s serial number and model number in the email.

  3. Reply

    ERD

    April 04, 2017

    With your air to water heat pump, in the summer could I have two active buffer tanks, one hot and one cold, with a 3 way valve to select between the two? Does the unit allow for using O signal to switch back and forth between heating and cooling often? Or it is meant to only be used occasionally depending on the season?

    • Jordann Brown

      April 06, 2017

      Hi ERD,

      Yes, our ATW Series heat pump can switch back and forth between heating and cooling in the manner you suggest, using two tanks would be the ideal way to achieve this.

  4. Reply

    fox

    September 03, 2017

    Helⅼo there! I could have sworn I’ve been to this site before but after reading through sߋme of the post I realized it’s new tο me.

    Anywɑys, I’m definitely deⅼighted I found it and I’ll be bookmarking and checking
    back often!

  5. Reply

    Carlos Morcate

    December 31, 2017

    We are in Clayton, NC 27527. Is it alright to run our unit’s auxiliary backup say at 25 deg F? Or at what min temp?, or simply shut it off untill there is a higher temp, say 35 deg F?

    • Jordann Brown

      January 02, 2018

      Hi Carlos,
      The heat pump’s auxiliary set point can be customized via the control board software. You can revise the temperature at which auxiliary heat takes over completely using that software.

  6. Reply

    Dick Goebel

    January 30, 2018

    Does anyone in Minnesota install these ?

    • Jordann Brown

      January 31, 2018

      Hi Dick,
      You should check out find a dealer tool on our website: https://www.nordicghp.com/find-a-dealer/
      If there isn’t a Nordic installer near you, we’ll work with any HVAC company that fits our criteria. For more information on that, you can email info@nordicghp.com.

  7. Reply

    Roger Stillwater

    November 27, 2018

    Just want to make sure I understand. A Mitsubishi mini-split heat pump claims to have Hyper-heat that allows for cold weather operation. I assume this is just a gimmick since the refrigerant, compressor etc are common technologies for all heat pumps. It may have sensors to trigger the defrost cycle efficiently, but that seems to be about all they can change. Do these type of mini-splits have a built in resistance heater for the defrost cycle or do they just not operate the interior fan when the system is cooling inside?

    • Jordann Brown

      November 28, 2018

      Hi Roger,
      I can’t speak with any authority to how the Mitsubishi mini-split works, but I would assume some type of electric assist is used to assist the heat pump in keeping the home warm during those super cold temperatures. The literature is a tad vague on this though. I would also assume that, like our heat pump, that electric resistance heating is triggered during defrost to prevent cold blasts of air on the homeowner.

      In terms of our heat pump’s lowest operating temperature, it’s currently set at -22C. In truth, we could have set it that cutoff lower, but that would cause undue stress on the heat pump and compromise the 20-year life expectancy of the unit.

  8. Reply

    Iris Meek

    August 08, 2019

    As a newbie to heat pumps I am anxious to learn more about operating my Mitsubishi

  9. Reply

    john devine

    January 15, 2020

    I cant seem to get answers any where else so I will try you. I have a airease 4SHP16LS136P and at 9 C it begins to run continually when temp set to 20 C, would you guess that this is possible or could there be something wrong, thanking you for any answer
    John

    • Jordann Brown

      January 15, 2020

      Unfortunately, we can’t provide any technical support for non-Nordic products.

  10. Reply

    Martyn Seabrook

    July 01, 2020

    If I have a stream that has a constant 12c Temp, can a heat pump be efficient at this temp? If so what is the efficiency?

    Regards Martyn Seabrook

    • Jordann Brown

      July 07, 2020

      Hi Martyn,
      The heat pump’s efficiency would depend on the type of heat pump you’re using, but 12C is appropriate for incoming water temperature and you can expect a COP of approximately 4.4

  11. Reply

    Bob Moreland

    July 06, 2020

    How many dB of noise are generated with the ATW units (indoor & outdoor) ?

    • Jordann Brown

      July 07, 2020

      Hi Bob,
      We have published sound ratings for the ATW Series on page 73 of the product manual, which you can download here: https://www.nordicghp.com/wp-content/uploads/2020/03/001970MAN-03-ISSUE-05-ATW-Series-Two-Stage-R410a.pdf

  12. Reply

    Aileen r STALVEY

    August 20, 2020

    What effect does it have on our GHP system if the well water temp is over 100 even 110 ?We are in a condo with near a 100 units. what is preferred temp to run our units ? How critical is it to add heat exchangers or cooling tower ?

    • Jordann Brown

      August 21, 2020

      Hi Aileen,
      Our heat pumps have maximum incoming water temperature limits. If the incoming water temperature is over that limit, you can reduce the flow through the unit.

  13. Reply

    Kerry Ridgway

    September 17, 2020

    We were advised by our utility company that we should check the operating temperatures with an infrared digital thermometer to ensure its operating efficiently. All well and good as we purchased one, but cannot find any data on what or where to test and for what temperatures. Is that a secret unique to each brand?

    • Jordann Brown

      September 18, 2020

      Hi Kerry, you can find recommended air output temperatures in our product manuals.

  14. Reply

    Ron Christie

    April 20, 2022

    We would like to install your air source heat pump to complement the solar arrays we are installing. I have a different question for you regarding your air source heat pump. As a farmer I use unheated high tunnels to protect crops through the winter. Could I enclose your heat pump in a similar structure with the idea of moderating temperatures and weather conditions. Temperatures almost never drop below 0 degrees F in the tunnels and are vented so that moisture does not build up on warmer days. Please let me know what you think.

    • Dan Rheault

      April 20, 2022

      Yes, you could do that. You’d want to make sure the area is not sensitive to moisture, since defrost condensate drips straight off the bottom of the air source outdoor unit (no drip tray). Also that there is not a significant air flow restriction due to being in a small tunnel; a booster fan to move air through the tunnel would help in this regard. Otherwise the unit could suffer from reduced air flow or cycling of cold discharge air back to the intake.

  15. Reply

    Jack Warner

    July 07, 2022

    I am buying an airtemp heatpump vsh1be series. I read somewhere on the internet that at 20 degrees I should turn on aux heat. I don’t know if that was for this series or not and I can’t find the article again and the distributor does not know! They need more training. Can you point me to the article or let me know

    • Dan Rheault

      July 24, 2022

      Hi, different manufacturers have different minimum outdoor temperatures, and I’m not sure about the model you mention. But Nordic air source heat pumps can operate down to -22°C / -7°F, below which the auxiliary heat needs to take over. At temperatures above that but still cold, auxiliary heat may still be required along with the heat pump, which will be activated automatically by the heat pump’s controller.

  16. Reply

    Henry Childs

    December 26, 2022

    Very interesting information provided by Nordic. Heat pumps have interested me since learning about them from my thermodynamics professor at the University of Texas back in the 1960s, where I obtained a bachelors degree in mechanical engineering.

    We currently heat and cool our home with an American Standard 3-ton heat pump, model 4A6H4036D100AB. I would like to enclose the outside unit, containing a heat exchanger, compressor and controls, in an air tight, water tight insulated housing. The plan is to install enough piping buried in the ground to circulate water to pick up or reject heat for the heat pump to operate efficiently in both heating and cooling seasons.

    A water to air heat exchanger of sufficient area to transfer heat to or from the geothermal water piping for the heat pump to operate effectively would be installed in the enclosed structure containing the heat pump compressor and heat exchanger.

    I believe this system would operate at lower cost with the geothermal circuit added and would have the advantage of never having to go through a defrost cycle in the heating season.

    To keep the cost of the heat exchanger for the geothermal circuit as low as possible I need to find a cost effective air to water heat exchanger to do the job. We live in Northeast Louisiana where the ground water temperatures are good and the Winters are mild. If you have any suggestions for materials I can use to construct the water to air heat exchanger it would be appreciated.

    • Dan Rheault

      December 30, 2022

      Hi, it can be fun to invent things of course. But note that it sounds like you are looking to construct a geothermal heat pump, which already exist and have standard installation methods; so it would be much easier just to buy one and have it installed.
      To answer your last question, water to air heat exchangers are normally made of horizontal copper tubes and vertical aluminum fins, and are custom manufactured using aluminum stamping and pipe expansion machines.

  17. Reply

    Dave Rush

    November 21, 2024

    My R-45 is a month short of 20 years old and the only thing that went wrong was a broken fan belt. The belt only lasted 16 years with about 1600 hours per year of run time LOL…. Can’t get much more durable than that.
    My groundwater to air is built like a Toyota and so simple, It can be easily maintained forever.

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