Vitosol 300-TM solar thermal system case study

Project Overview

Sitting 1,000 ft above sea level, in an exposed location within the Dartmoor National Park, the Wage Captain’s House was on the market for some time. Numerous offers were rejected by the National Park as potential buyers and developers planned to demolish the building, rather than restore it. The property had fallen into disrepair in the late 20th Century on the closure of the clay pits, and its protected status as a post-industrial heritage site by National Park made its restoration a seemingly overwhelming and unprosperous prospect for many. But for Mike Hope, Managing Partner of Roderick James Architects, and his wife, it was the perfect fit.

Since purchasing the Wage Captain’s House in 2007, working in close partnership with Darren McCabe of Enhanced Energy Ltd, Mike has transformed the property with his eco-conscious ‘build tight, ventilate right’ approach. Flat-roofed, unattractive concrete extensions were demolished, and materials (including blockwork, timber and metals) reused, repaired or recycled. A timber frame was then constructed to maximise living space for the family of five, whilst still retaining the property’s protected south-facing elevation and original ‘T’ shape.

As the building developed, so too did its heating system. Once an air source heat pump (ASHP), underfloor heating, energy store, heat recovery and ventilation system, and wood burner with back-boiler were installed and running, the next step for Mike was always going to be solar.

“Because National Park planning is difficult to secure, I wanted pre-rule for everything, so I included the solar technology on the approvals plans right from the start,” said Mike. “I wanted solar thermal rather than solar PV as I know the tube system is more efficient – more expensive, yes, but worth the investment.

“The solar panels were the last piece of the jigsaw to reduce the demand on the ASHP and therefore the electricity demand, and therefore the overall carbon footprint of the house.”

The Problem

But when it came to finding that last piece of the puzzle, this unique property posed characteristically unique challenges.

Firstly, the building’s distinctive corrugated tin roof and lack of rafters meant installation would be trickier than on more traditional, tiled properties. Added to this, the protected nature of the property’s south facing elevation meant that the collectors could not be sited in their optimum position, where they would not be visible from the front.

Things were further complicated by the unusual and also protected T-shape of the building, as well as by several beech trees that overhang the property at the rear. Together, these limiting factors meant the only available space to fit the solar thermal technology was a smaller, inner roof.

The Solution

McCabe recommended using the Viessmann Vitosol 300-TM solar thermal system using a high-performance vacuum tube collector. It is particularly suited to tight spaces as the absorber angle can be adjusted by up to 25° to deliver an exceptionally high yield, even when placed in less favourable positions.

High grade, corrosion-resistant materials, including glass, aluminium, copper and stainless steel also protect the Vitosol 300 from the weather influences associated with the property’s exposed location on the Dartmoor National Park, making it the perfect choice.

To help installation, timber roof purlins were installed during the building works to which the metal roofing sheets could be fixed. The exposed fixings were easy for Darren to spot, and these provided suitable fixing points for the solar panel mounting rails. Fitting the panels in less than two days, Darren was able to conceal the collector under the panels, and ensure pipework avoided the new oak frame.

Energy collected by the panels travels through the collectors into a 300-litre thermal storage cylinder with twin coil where it is stored as hot water until needed. Along with smart controls, the cylinder is housed in a purpose-built cupboard. Servicing the panels should be more straightforward than other systems as the Vitosol’s heat pipe tubes can be replaced quickly and easily without having to drain the system, due to their dry connection.

The Results

Darren designed the system to provide 52% of the property’s hot water from the solar panels, with the ASHP backing up the remaining 48%. Mike keeps a close eye on the system’s performance and is keen to see how things progress. “This is the next part of the experiment I suppose you could say,” he says.

“We’ve already halved the hot water heating time. It was timed to come on in the morning and then be boosted in the evening, but at the moment we’ve got it coming on in the morning and that’s it! The solar panels do the rest of the work during the day. In summer months, I imagine we’ll turn off the morning heating and the panels will do it all. The great part is that the thermal store will hold any excess energy generated by the panels, to reduce the demand on the ASHP, even for the underfloor heating.”

Mike intends to reap further rewards from the new solar technology, by claiming funding under the Government’s Renewable Heat Incentive (RHI). The 1,329 kWh/year deemed renewable heat generated by the panels means Mike’s estimated annual income from the scheme is £285.60. This is in addition to the 929.37 kWh/year fuel saving and £148.70 cost saving the system is predicted to make.