How Quilt solved the biggest heat pump challenge

Smart home startup Quilt on Tuesday introduced a three-zone heat pump that promises to maintain efficiency even in the kinds of demanding conditions that thwart traditional incumbents.

The three-zone unit does what it says on the label: One outdoor unit is now capable of driving three indoor heads, as they’re called in the HVAC world. It’s a product that will make large installations simpler and cheaper while minimizing the footprint outside the home, and it’s key to the startup’s expansion plans, which have been recently turbocharged with a $20 million Series B focused on sales expansion.

But the real story is how Quilt developed the new product.

Since its inception, Quilt has prided itself on the amount of data it collects from its heat pumps. Not only are they connected to the Internet, but they are also equipped with more sensors than traditional heat pumps.

By analyzing this data, Quilt engineers were able to do things that other companies had not been able to achieve. In September, for example, they sent a live update to heat pumps in houses which freed up an additional capacity of 20%, which could be directed towards one or two zones. With the free update, people could be more comfortable during heat and cold waves.

The team also used the data to develop the new three-zone unit and, in doing so, solve a thorny challenge many competitors face.

Like all heat pumps, multi-zone units work best when operated at variable speed: When heating or cooling demand is low, the compressor operates at a lower speed to provide only the amount of heating or cooling needed.

But there are limits to how high they can operate. Compressors become less stable at low speeds, making them more difficult to control. Matthew Knoll, co-founder and CTO at Quilt, compares it to driving a car at low speeds. Maintaining a constant speed of 70 mph is easier than maintaining a constant speed of 11 mph. “It’s a little more difficult,” he said.

To compensate, most systems shut off the compressor at a certain point, sacrificing some efficiency and comfort in the process.

Quilt, however, was able to draw on data collected from the thousand or so units already installed in homes and businesses, giving them insight into how the systems worked in the real world.

“The way most systems are developed, they’re tested in the lab in multiple scenarios, because testing is expensive. And you end up with kind of an average product,” Knoll said.

“We have a thousand units in many different climates, and if we see something, we can look at it on a set of different units to understand if there is room to optimize or if we see a problem in a particular case,” he said.

The company also uses a larger copper coil than many competitors, allowing it to specify a smaller compressor. This combination, along with a few other design changes, allows Quilt to deliver nearly 90% of its rated capacity (27,000 BTUs) at -13°F (-25°C) without sacrificing performance or efficiency at low demands. Quilt claims it is the most efficient three-zone mini-split on the market.

To save energy, each interior head can be controlled individually, providing as little as 2,210 BTUs of heat or 1,570 BTUs of cooling. If heating or cooling is not required, refrigerant still circulates through the lines as in other heat pumps. But thanks to the outdoor unit’s low-speed performance, it only releases about 300 BTUs of heat in heating mode. That’s about as much heat as a full-grown adult puts out.

Where does Quilt go from here? Knoll would not comment on future plans, except to say that Quilt “wants to be able to have a solution for every home.” More products are coming, and it’s likely that plenty of data will help guide their development.