Why This Window Heat Pump Is Genius

I know, I know. I talk a lot about heat pumps, but there’s a good reason for it. It’s a fantastic technology that uses a little physics exploit to get more heat energy out than energy you put in. The problem is that most of the time, the devices I’m talking about are for homeowners that can easily retrofit new installations into place — or, in my case, drill a massive ground loop well for a geothermal system. That’s definitely out of reach for most. So where does this leave renters?

Well, there’s a new type of heat pump hitting the market that’s a little more accessible: easy to install heat pumps that sit on your window just like an AC unit. It seems so obvious when you look at it that I can’t help but wonder…why didn’t we do this earlier? And how well do they actually work and at what cost?

Trending

Top 5 Solar Energy Advances Using Perovskites

I’m sure a lot of you have been stuck in situations where you’re at the mercy of an antiquated heating and cooling system. For example, how do you adapt to an apartment building that’s 100 years old and heated with a gas steam boiler system that you have no control over? It’s heating to the lowest common denominator, which means some apartments are cozy and others are cooking. In a situation like that, sometimes the only available option is to crack windows open in the dead of winter. Not a great way to conserve energy and save money. This is a pretty common problem in many older buildings in US cities like New York and Boston.¹ I know … I lived in a unit just like it.

New York City Pushing the Envelope

It’s through window heat pump units that New York City is leading by example when it comes to heat pump adoption in the United States. In accordance with the city’s Local Law 97 of 2019, buildings in the Big Apple are now required to make massive cuts in greenhouse gas emissions over the next few decades.² The goal is to reduce emissions by 40% by 2030 and by 80% by 2050. To hit that target, the New York City Housing Authority (NYCHA) is focusing on improving heating and cooling systems within its public housing networks.This means landlords need to start upgrading antiquated and inefficient boiler systems in public housing across the city, which affects more than half a million people in over 2,400 buildings.¹

Radiant systems and steam-based boilers, while fairly efficient, are not as efficient as heat pumps. Large steam systems are complex, prone to energy leaks, and only about a third of their input energy is converted into useful heat.²

The New Heat Pumps

And that’s where window heat pumps come into the picture. When I first saw reports of these all I could do was this. You can see right off the bat what makes these designs unique: the “inverse U” or “saddle-style” design that doesn’t obstruct the window’s view. It’s easy for residents to install it themselves in about half an hour or less without the need for a professional… or wrecking existing structures. And the icing on the cake? No electrical upgrades necessary either. These heat pumps run off standard 120v AC outlets. This puts temperature control back into the hands of residents and makes it all more efficient thanks to the power of the heat pumps. You can have your heat pump cake and eat it, too.

There’s other convenient features that window heat pumps offer as well, like relatively smaller footprints, low noise levels, and condensation management systems.³ That means no excess water dripping down buildings, external hoses, or trays. These also help reincorporate humidity into dry air.⁴ There are even some early anecdotal reports that they’ve literally helped residents breathe easier.⁵

A window heat pump’s components won’t be much of a shocker to those who are already familiar with traditional heat pumps, but here’s the basics. It’s got a compressor, condenser, evaporator, and a reversing valve that allows it to switch between heating and cooling modes. These are all housed within one compact unit that fits within a window. Since heat pumps move heat rather than generate it, from something like an electric resistive heating element, you’ll get 2-3 times more heat energy out than electrical energy you put in.⁶⁷

That’s why in 2021, the New York Power Authority (NYPA), New York State Energy Research Development Authority (NYSERDA), and the NYCHA launched the Clean Heat For All Challenge. This involved investing $263 million into advancing electrification efforts to meet New York’s climate and energy goals. The idea was to promote new designs that could slot into existing infrastructure and eliminate the high costs normally associated with rolling out heat pumps to apartments.⁸

What’s Hitting the Market?

Who ended up taking action and rising to the challenge?

That would be Midea US, headquartered in New Jersey, and Gradient, based in San Francisco. As the winners of the challenge, Midea will provide 20,000 heat pump units to a NYCHA pilot project, while Gradient will supply 10,000 units.⁸ Let’s look at Midea first.

Midea

Midea’s Packaged Window Heat Pump, or PWHP, not only represents the lionshare of the challenge winnings, but it also earned itself the prestigious AHR Expo Innovation Award this year.⁶ That’s a convention held by ASHRAE, or the American Society of Heating, Refrigerating and Air-Conditioning Engineers. The heat pump is specifically designed for DIY installation.⁹ As you can see here, the body has handles built into it to help easily slide the unit over the windowsill.

The PWHP can provide 9,000 BTU/hr of heating and cooling. Then there’s its coefficient of performance, or COP. The COP is a measure of a heat pump’s efficiency, based on a unit’s heating capacity vs the amount of electricity it uses. It’s a handy metric for comparing heat pumps against each other and other forms of heating.¹⁰ Midea’s heat pump has a COP of 2.35 at temperatures as low as 17°F (-8°C). For comparison, anything that burns fuel like a furnace or boiler is going to have a COP of 1 or less. And the PWHP can operate at temperatures down to -13°F (-25°C) without auxiliary heat and all the way up to 113°F (45°C).⁶¹¹ Meaning that this unit should be able to easily handle those cold New York winter nights or hottest of summer days. On the flipside we have the CEER, that’s the Combined Energy Efficiency Ratio, which measures the efficiency of room or window-mounted AC units. Midea’s heat pump scores a 16, which puts it at or above the scores of most high end window AC units on the market.¹²

Gradient

Now let’s look at Gradient, who are set to supply their own All-Weather 120V Window Heat Pump. The numbers on this heat pump will look pretty familiar to you. This heat pump also has 9,000 BTUs of heating or cooling, and an easy to install window-mounted frame. It maintains a COP of 2.60 all the way down to 17F (-8C), and keeps functioning down -7F (-21.7C).¹³ The high end of the range is 95°F (35°C), which should handle the typical temperature range of New York. This heat pump also plugs into a standard wall outlet and is made with DIY installs in mind. Gradient claims you can do it yourself in just 15 to 20 minutes.¹⁴

Gradient has boasted about their use of R-32 as a refrigerant. In the past many refrigerants were pretty harmful to the environment or the ozone layer. But R-32 scores a big fat zero in ozone depletion potential (ODP), and has a global warming potential (GWP) of around 675. That might sound rough on first blush, but that’s actually close to a one-third of the GWP of more common refrigerants.¹⁵ Gradient’s heat pump is efficient too, it has Combined Energy Efficiency Ratio (CEER) 10.8, qualifying it for a coveted (but not uncommon) EnergyStar award.¹⁶

So, for what it’s worth it seems like the Gradient heat pump is slightly more efficient at the mid range temperatures and is alleged to be quicker to install. But Midea’s take on the window heat pump has better effective temperature range and a better Combined Energy Efficiency Ratio (CEER). Both look to be great options.

Pros & Cons

What do these heat pumps mean for New Yorkers? Well, we’ve already covered a lot of the quality of life benefits they offer to residents, but let’s look at them versus older boiler technologies that these window units are trying to replace. Whether it’s a gas/oil boiler, a condensing boiler, a steam boiler … it doesn’t matter because none of these older technologies are going to break a COP of 1. Even an electric radiator is going to score a COP of 1, so for energy efficiency the window units win out.²

Things start to get fuzzier when it comes to the cost. Traditionally, the pricey nature of heat pumps has been their biggest stumbling block. Both companies have noted that they want to make sure their heat pumps are affordable, and NYCHA wants them to keep the cost below $3,000 dollars. Midea says their pump will cost $3,000 on the dot, while Gradient says their unit will be around $2,000, but their current model runs you $3,800.¹⁷¹⁸ For comparison a window-mounted AC unit only costs a few hundred dollars on the low end, but it can only cool your home.¹⁹ These window heat pumps heat and cool, which AC units can’t do. They’re also far more efficient than any tiny space heaters systems you can install. On top of that they also use more eco-friendly refrigerants than many of the aging window AC units apartments like this are probably using … but that’s still a lot of money for all those benefits.

Plus, there’s always the chance that manufacturing or supply chain challenges could put the final market price even higher than the hoped-for price. We’ve seen it happen with plenty of technologies before. On the other hand, heat pumps are generally eligible for rebates or tax deductions, like the Inflation Reduction Act (IRA) here in the US,²⁰ so that could help ameliorate things. Even with rebates and tax incentives, heat pumps are still likely to be a big upfront investment for a renter or landlord to recoup that cost slowly over time.

This all makes the math of heat pumps vs retrofitting the old boiler systems pretty hard to calculate. Instead of getting a window heat pump for every resident, the owner of a large building could replace the old gas boiler with an industrial heat pump. That heat pump could feed hot fluid to radiators, underfloor heating, and the like. In these old buildings though, you’d still run into that issue of heating to the lowest common denominator, which would undercut much of the energy efficiency gains. I’m having flashbacks to my Boston apartment again. It also doesn’t address the need for cooling, which can be a major issue during summer heat waves in cities like New York. There’s an overall quality of life issue that these heat pumps can address that makes it hard to put a number on. And again, if you’re not allowed to remodel part of the building because it’s a historical landmark or due to mold or asbestos fears, then window mounted would be the way to go, regardless of price. What I’m trying to say is there’s a lot of variables to consider here!

There’s also concerns about electricity usage. In many apartment buildings heat is included in your rent, but you pay for electricity yourself. Shifting to these window heat pumps means that renters will be taking on their heating and cooling costs in their electric bill. That’s an incentive for a landlord to make the switch because it reduces their cost for running the building, but the switch will hit a renter’s bottom line. However, as a renter, you’ll have complete control over how much you run the unit and at what temperature. Collectively, 30,000 heat pumps are going to draw a lot of electricity. The agencies involved don’t think it will strain the grid. If everything goes according to plan and window mounted heat pumps take off, what will 3.64 million new heat pumps working night and day do to the grid?²¹ Probably not nothing!

Outlook

And while there are some concerns about strain on the grid, the efficiency of heat pumps means they’re likely to be better than all the other climate control devices currently in use. Gradient estimates that the yearly energy cost of running their heat pump to be between $64 and $238.²² There’s a lot of variables that go into that figure, so the exact price will vary a lot. However, that’s still a good deal. Especially compared to your average air conditioner which will cost you between $172.80 and $2,534.40 per year.²³

Take those operational savings and spread it across not just New York, but other cities that are interested in similar bulk orders of these heat pumps, like Jersey City, Boston, and Seattle. Together, they represent almost 24,000 apartments.²⁴ An estimated 39 million Americans in general live in apartments, and that number is only going to go up.²⁵ America, of course, isn’t alone. Lots of cities like Tokyo, Toronto, or Beijing have apartment dwellers who could benefit from heat pumps like this.

While upfront cost may remain a speedbump, it won’t surprise you to hear that I’m pretty bullish on these window-mounted-variety. Again, I know I love heat pumps, but shrinking ‘em down a bit and tooling them for smaller spaces, like apartments, just seems like the natural next step in their evolution.