A New Kind of Window Air Conditioner that Heats and Cools
A Midea Saddle-style window-mounted cold climate heat pump
By Mac Robinet
Window air conditioners that provide both heating and cooling are finally here. They are called Saddle-style window-mounted cold climate heat pumps. In addition to providing both heating and cooling, they are designed not to block the window view. The inside fan with the condenser/evaporator, and the outside compressor, sits over the windowsill like a saddle so the window sash can almost close completely. And windows can still be opened and closed anytime. They will fit in any single or double-hung window that is at least 25.5 inches wide and 24 inches above the floor. They are easy to install (less than an hour), require no drilling or permits, and use a standard 120-volt, 15-amp outlet. They are as quiet as a very quiet refrigerator.
Background
This new format of heat pumps was “created” by the New York Housing Authority as one way to reduce their emissions. They were committed by law to reduce greenhouse gas emissions (GHG) 40% below 1990 levels, and then 85% by 2050. They issued a “challenge” to the industry to develop a window-mounted heat pump capable of 9,000 BTU heating and cooling and operating down to -13 ºF without electric resistance heating. An additional requirement was to use a low global warming potential (GWP) refrigerant.
In July 2022, two manufacturers, Gradient and Midea America, were awarded contracts to produce 20,000 heat pump units,10,000 to Gradient and 10,000 to Midea America. Those installations are still ongoing. The Gradient units are made in San Francisco, California, and the Midea units are made in China. Midea appears to have decided not to sell units outside its contract with the New York Housing Authority.
Side view of a Solius Air 12,000 BTU Saddle heat pump
Cost and features
The current cost of the heat pump from Gradient is $3,800 per unit if only one is purchased, and somewhat less if purchased in large quantities. (The purchase phone number for Gradient is 1-610-310-1169)
Gradient gave a lot of attention to small details. For example, in the heating mode defrost cycle, ice on the outdoor coils is melted, and some of the collected water is misted inside to increase the humidity. Because the system is inverter-driven, it can run at very low speeds, so it is very effective in decreasing humidity when in the cooling mode.
The coefficient of performance (COP) of the Gradient heat pump is about 2.6 (at 17 ºF), meaning that its output is 2.6 times its input. It is 2.6 times more efficient than a 99% efficient gas boiler. It is a cold-climate heat pump, so it can provide full capacity down to 5°F and continue to function at -13°F. The Gradient 9,000 BTU heat pump can typically heat and cool rooms of about 400 to 600 square feet.
These heat pumps could be used almost anywhere there are windows. In fact, they could be used to supplement or back up a whole-house heating system. They are especially suited as a replacement for radiators, and to add cooling in apartment buildings. However, savings would be greatest if everyone in a building switched, so none of the existing gas-fueled boilers would be needed. Otherwise, households with heat pumps might have to continue to pay for gas heating that is included in their rent. Nevertheless, because these heat pumps are so efficient, they could have a significant impact on reducing our emissions. They could help us meet our Climate Ready Oak Park goal of reducing emissions by 60% below the 2019 level by 2030.
Emissions reduction
For those who are scientifically oriented, let’s quantify the impact of one heat pump.
Our emissions from the use of gas in residential buildings are currently about 120,000 metric tons CO2e per year. Sixty percent of that is 72,000 metric tons CO2e per year within the next five years, and the average is about 14,200 metric tons CO2e reduction by the end of this year. (For simplicity, we are using the current emissions rate as the reference rather than the 2019 value.)
If we were to use a Gradient 9,000 BTU per hour heat pump for about 12,000 hours in five winter months, we would avoid using about 84 million BTUs per year from gas. That would avoid the emission of about 6 metric tons of CO2e per year. [Assuming a 0.9 efficient gas boiler and an emissions factor of 53 kilograms CO2e per million BTUs for natural gas. That is, (9,000 BTU/h x 12,000 h/year) ÷ 0.9} X 53 kg CO2e/million BTU =6,360 kg CO2e/year =6.4 metric tons CO2e/year]
The reduction of 6 metric tons per year from just one heat pump versus a goal of 14,200 metric tons for this year is tiny, maybe insignificant. But a hundred or a thousand heat pumps would make a meaningful difference. Of course, larger heat pumps are essential to make a larger impact.
The beauty of using heat pumps is that the emissions reduction is easy to quantify. Unless we know and understand the quantity of our emissions and we can quantify our reductions, there is not much incentive to act.
In the residential sector, it is all about reducing emissions by reducing the use of natural gas. A solution, perhaps the only solution, is to switch to electric heat pumps of any size, shape, type, or color as soon as possible.
Make it happen now
To accelerate the process, the Village of Oak Park should consider purchasing a few Gradient window heat pumps for demonstration in various parts of the Village. Two or more could be loaned for a week for households to try. One or two could be raffled. Based on need, window heat pumps rather than grants could be given to renters and condo owners or those with radiator heat. Heat pumps could be purchased in large quantities at reduced costs as part of the energy efficiency grant program and could be marketed to both homes and businesses.