SunPump Pumps New Life Into Solar Thermal Heating

A heat pump is basically like a fridge, moving heat from one place to another. Ground source heat pumps move it from the ground to the inside; Air source pumps suck the heat out of the air. All heat pumps work the same way, with a refrigerant absorbing heat by evaporating and releasing it when compressed and liquified. The SunPump is one of those "why didn't anyone think of this" ideas where the refrigerant is pumped into solar panels on the roof where the heat of the sun acts directly on the refrigerant, making it really efficient. At the other end, the heat is extracted and used to heat water in a "thermal battery" or hot water tank, which can then be piped to radiators, radiant floors or heat exchangers for forced air.

This solves a lot of problems. A few years back we wondered whether solar thermal systems made sense in a world of cheaper photovoltaics; they were complex and not all that dependable in climates where there was not pretty much constant sunshine. The SunPump relies on a refrigerant with a boiling point of -50°C so it will work (albeit not as efficiently) in the dark of night. It has a COP (coefficient of performance) of 7 in the sunshine and 2.7 at night.

I have also often wondered whether ground source heat pumps really make sense, given the cost of the drilling and the piping, when air source heat pumps cost so much less; the geothermal supporters call me a misinformed idiot and tell me that they are really using a renewable resource, the heat of the sun that's stored in the ground. The sun pump does away with the ground and the drilling and the piping and uses the sun directly.

© Sunpump

As an extra bonus, Sunpump is now bonding their thermal panel to a photovoltaic panel; as the refrigerant evaporates and absorbs heat it will keep the PV panel cool, significantly increasing its efficiency. And like any heat pump, it can cool as well; instead of sending the refrigerant to the roof it loops it to a coil, making it a very efficient air conditioner that moves the heat from the inside air into the domestic hot water tank.

The rationale for solar thermal being dead came from research by Martin Holladay of Green Building Advisor, who noted that in most northern installations they delivered an average of only 63 percent of hot water used, and needed a backup electric system for the balance. The SunPump is a solar thermal system that can run all the time and deliver 100 percent of hot water needs for both domestic and space heating (although it does have an internal electric element just in case). Back in 2014 Holladay was skeptical about how dependable it was or how "easy it is to run refrigerant in leak-free tubing from a heat pump to collectors on your roof."

But SunPump has now done quite a few installations across Canada, has solid financial backing, a new name and a new website (with too much Lorem ipsum still showing). They claim it is pretty reliable:

It is an elegantly simple appliance, with just one moving mechanical part, a DC scroll compressor, common in refrigeration and heat pumps that can run for decades. The refrigeration technology has been maturing for more than 100 years. It is the size of a mini-bar fridge and works about the same.

In a Passive House or other highly insulated home where one doesn't need much heat, the smallest SunPump could easily handle all the heat and hot water; they even have a special coil to stick on the Heat Recovery Ventilator.

So perhaps solar thermal really isn't dead at all; it was just pining for an upgrade to heat pump tech. More at Sunpump. And here is a video of an installation: