10 reasons for choosing solar heat

In this column over the past few years, I have described the standardized methods and best practices we use to install solar hydronic combisystems most successfully. Using what I call the “New Standard” in solar/hydronic strategy, our solar-heated building installations are now faster to design and easier install. A repeatable design configuration with an integrated control yields successful results that are predictable and verifiable using remote monitoring and control over the Internet.

Using this approach, our solar heating and renewable energy combisystems are no longer experimental or “one-of-a-kind” customized creations. We now employ more of a “cookbook” approach, combining familiar ingredients with familiar patterns and modular configurations for rapid and reliable deployment. In our experience, solar hydronic heating in buildings has never been more practical or more reliable. 

Just Do It: The Solar Heating Decision

In the construction world today, solar hydronic buildings are relatively rare, and solar space-heating seems to be something of a forgotten art. But with the New Standard design methods, we found that the implementation of solar hydronic heating has never been easier. There is no renewable energy technology better fitted for the hydronic plumbing and heating industry. 

Looking back on dozens of successful installations in recent years, here is a list of the top 10 reasons why the solar heating option was chosen for these projects. 

1. The climate is “sunny enough” and the collectors will fit. In our sun-belt climate, where it is typically 85 percent sunny, an 85 percent solar-heated building can certainly be achieved. But we also have completed successful solar heating projects in places such as Oregon, Alaska, Rhode Island and Virginia, where the annual sunshine is considerably less, but still proved to be worthwhile. 

In climates that may seem questionable, the only way to tell if it is sunny enough for solar heating is to model the project using local climate data. When the calculations show that a climate has enough solar energy to contribute significant fuel savings, a solar heating system is born, even in some unlikely places. 

Of course, there must be a good location for the required solar heat collectors. There are many other ways to make solar heat collectors fit into a construction plan, including various roof mounts, wall mounts and ground-mounted racking systems with different tilts and configurations.

2. A hydronic hot water boiler system will be there anyway. Hydronic hot water boiler systems are easily compatible with New Standard solar hydronics. In these systems, hot water baseboards, radiator panels or fan coils are typically used for heat distribution. Also commonly included are radiant floor heat zones and an indirect domestic hot water (DHW) tank. Swimming pools, ice-melt zones and heat-storage tanks are frequently connected to these standard systems.

Figure 77-2 shows a piping diagram of an example solar/hydronic installation using the New Standard piping configuration. The hot water boiler equipment that has to be there anyway is seen in black. Our standard solar heating configuration is in red. 

Notice that the black conventional heating equipment makes up the majority of the total heating equipment. You can see how the red solar equipment may optionally be added later using two-pipe stub-outs on the primary loop if a solar-ready heating system is desired.

3. Masonry radiant floor heat will be there anyway. Masonry radiant floors are commonly made of concrete with embedded PEX tubing. Solar heat can be delivered to the concrete by circulating warm hydronic fluid through the PEX tubing. The concrete has a substantial specific heat capacity, which translates into a large heat storage capacity — aka thermal mass. 

Our standard control strategy uses the thermal mass of the concrete as a “solar heat accumulator” within a carefully controlled temperature range for human comfort. When the thermal mass of the building is used for heat storage like this, we can reduce or even eliminate the need for large, heat storage water tanks or other more exotic and expensive heat storage systems. 

Notice that in Figure 77-2, the heat storage tank is plugged into the primary loop in a way that makes it easy to include it or eliminate it, depending on the needs of the building. Sometimes the absence of a big heat storage tank is the deciding factor in allowing a project to go solar thermal.

4. Heating will be a significant annual energy cost. The average residential home in the United States uses about 65 percent of its yearly energy consumption for combined space heating and DHW. This heating energy is not typically offset when photovoltaics (PV, solar electricity) are installed but can easily be offset with solar heat collectors in many types of buildings. 

Despite the vast proliferation of PV panels and exciting advances in “zero-energy” building techniques, these technologies have not made a dent in the heating energy consumption in buildings. This represents a huge opportunity for efficiency improvement. Since most of us live and work in buildings requiring significant amounts of heating energy, it makes sense to use available, proven technology to offset conventional heating fuel consumption wherever we can.

5. The local cost of conventional heating fuel is high. When the cost of fuel is high, the savings from a solar heating system becomes more valuable as well. Many of our clients who depend on propane, fuel oil, diesel or electricity (from the grid) for their conventional heat determined that the savings from solar/hydronic heat provide an attractive cash flow improvement. 

The steady supply of solar heat over the years may be considered a kind of insurance against the rising cost of heating fuel over time as well.

6. There are other alternative sources of hydronic heat. The New Standard solar/hydronic piping configuration allows multiple heat sources and multiple heat loads to be centrally connected and intelligently controlled. So, the system can accommodate other numerous heat sources, beyond the example seen in Figure 77-2, where there are three common heat sources: boiler, solar heat collectors and heat storage tank. 

In some past installations, we included other unconventional heat sources such as a wood-fired hot water coil, ground-source heat pump, waste-heat recovery from an engine generator and heat recovered from a refrigeration air-conditioning system. Sometimes the New Standard hydronic configuration is chosen because it can seamlessly mix and match a wide variety of renewable heat sources.

7. The building includes a large heated water feature. It is not unusual for a facility with a large water heating load to look to solar heating as a way to manage the heating fuel consumption. A commercial water heater at a hotel or a car wash, for example, is always worth considering. 

Also, a heated swimming pool or large hot tub is easily included in the heating loads connected to a New Standard heating system. A large pool may benefit from solar heat even at times when nothing else in a standard system needs any heat, thus extending the usefulness of the existing solar collectors. 

Any large water heating load that is persistent throughout much of the year is a candidate for regular and substantial fuel savings from a properly designed solar heating system.

8. Green motives such as carbon offset, near-zero-energy. Some building projects are guided by green or sustainable objectives, such as a high LEED rating or a small carbon footprint, as seen in net-zero or near-zero building energy designs. Since solar heat is capable of offsetting large amounts of combustion fuel, it is capable of preventing large amounts of combustion products from being generated, specifically large volumes of CO2. 

This can be a strong motivating factor for a green end-user to choose hydronic solar heating. 

9. Self-reliance or emergency preparedness. Some of our most interesting solar combisystems are installed off-grid or are designed to operate normally off-grid during outages and emergencies. Solar heat and other alternative heat sources can go hand-in-hand with off-grid PV electric power, generator backup, wood boilers and other technologies commonly used in self-sufficient installations. 

The New Standard hydronic heating configuration can be applied to off-grid self-reliant installations and is sometimes used for that purpose.

10. Tax rebates or other financial incentives apply. Sometimes the final decision to install solar heat is inspired by rebates and incentives. State and federal incentives are summarized most conveniently on the DSIRE website at www.dsireusa.org. In many instances, the same financial incentives often associated with PV systems are available for solar heating equipment, as well.

These 10 reasons apply equally well to new buildings, retrofits and remodels. Not all of them need to apply for a favorable decision to go solar thermal; just one compelling reason can sometimes be enough. As a general rule, if three or more of these reasons apply, then a solar heating system probably makes sense.

Note: These columns are targeted toward residential and small commercial buildings smaller than 10,000 square feet. The focus is on pressurized glycol/hydronic systems since these systems can be applied in a wide variety of building geometries and orientations with few limitations. Brand names, organizations, suppliers and manufacturers are mentioned only to provide examples for illustration and discussion and do not constitute any recommendation or endorsement.