Solar thermal is a perfect renewable heating option for schools, says Colin Bland, renewable sales team manager for Viessmann.
Solar thermal still offers the best output per square metre of energy and in most cases, solar thermal in conjunction with a condensing gas boiler offers the most suitable and efficient renewable system. Local authority leisure centres and nursing homes have long realised this and they represent a large part of our customer base. Yet, solar thermal is often disregarded as inappropriate for schools.
Solar works best when generating hot water during the summertime when the solar-generated heat can match the peak load requirement. Unless they have swimming pools or shower blocks, schools do not generally consume large amounts of hot water and are closed during the summer holiday period. However, solar is always a good solution, even in a school with lower hot water requirements (see the calculations below) and facilities managers should not be overly concerned that they will miss out on potential savings or fall foul of solar stagnation issues.
Most schools are only closed for a total of six weeks in summer, and as we know, July and August are not necessarily the sunniest months of the year. Remember, even for domestic properties there are several weeks per year where there is no hot water draw. Solar systems can be designed to deal with stagnation that may occur as a result of not being used for a longer period of time. The sizing of the system is key and a hot water usage assessment is always the first step. Sizing is always based on delivering base peak load in the summer, which is often before the school closes for the summer holiday. For a school with only washbasins and kitchens, we would estimate a standard usage of 2-2.5 litres per person per day.
Viessmann has solar calculation software which ensures an appropriately sized cooling vessel and expansion vessel that limits water falling into the ‘steam zone’. This is designed for systems that are anticipated to stagnate and provides greater protection for the glycol medium and temperature affected components. Additionally, components such as ‘stagnation coolers’ can be added to the system to accommodate the expected conditions.
Factoring in the Renewable Heat Incentive
Let’s look at how the RHI affects the solar thermal proposition for schools. Taking a school with low DHW usage (i.e. washbasins and kitchens only) and 10,000 kWh annual heat demand, the total cost of ownership of a solar plus condensing boiler system over the 20 year RHI guaranteed payback period would be around £142,000. This is a saving of around £12,000 over a new boiler replacement alone. Factoring in loan costs of 6 percent interest annually, the difference is a modest £4,000 but still worth it. The savings are a considerable £66,000 compared with the option of not replacing a typical older generation boiler with 65 percent efficiency – remember the solar figure includes the installation cost. This is the real call to action for those looking after public building heating systems and weighing up whether it makes sense to replace aging boilers.
The case for solar thermal is much stronger, as one might expect, in a school with double the annual DHW heat demand. Here, the financial saving from adding solar rises from 32 percent for the low demand to 37 percent. Furthermore, 10,000 kg of CO2 emissions are saved each year compared to the incumbent old boiler.
Solar and Wolverhampton City Council.
Wolverhampton City Council trialled solar thermal at Kingswood Nursery and Infant Centre, a residential outdoor education centre providing day and overnight residential visits for children aged three to eight years, about five years ago. It marked the start of a relationship with renewables that has seen a number of subsequent solar thermal installations in schools and equipped the council with the knowledge to help it exploit the new Renewable Heat Incentive.
With hot water draw from a 12-shower wash block, in use all year round, solar was a natural choice for Kingswood, says energy manager Keith Daw, who monitors energy usage and oversees energy-related building and maintenance projects for Wolverhampton City Council’s public buildings. “Kingswood was a perfect showcase for our first solar thermal installation because so many schools and other community groups from around Wolverhampton come here and we have been able to show them how solar works,” he says. The building benefitted from a Viessmann Vitosol 300 solar panel and two Vitodens 300 gas boilers.
Daw says a recent change to the way the council finances facilities management projects has enabled him to give the green light to more renewable heating and microgeneration installations. “We have switched from using an external investment fund, with rather prescriptive payback terms, to introducing our own,” explains Daw. “This allows us to work to our own rules and to introduce more flexibility. We know our city and the demand – short and long term – on its purse strings. We can make choices based on our deeper knowledge of the projects and their potential, whether in terms of payback or whole life costs. It’s been good news for renewables and schools because we can offer longer payback periods.
“Now, if a boiler replacement project comes up, we can suggest the school looks at solar thermal in addition to a modern condensing boiler. Although the initial investment is larger to add the solar, with the RHI, we are going to get tariff payments back into the pot that weren’t there before.”
Further renewable installations at Wolverhampton City Council include solar thermal at a special school, which has a hydrotherapy pool. A combination of solar and two Vitocrossal gas boilers meets the building’s demand, including heating up the pool to 35° C. There are currently plans to exploit the RHI tariff for biomass boilers with installations of Viessmann’s biomass unit at three to four sites.
About Colin Bland
Colin Bland is Viessmann’s sales manager for renewable energy systems. He heads a team of six area business managers covering the entire UK, which is tasked with growing the company’s renewable energy business. He has 30 years experience in the plumbing and heating industry, including running an independent builders merchant.