Rules of Thumb for Ductless Minisplits

first_img Start Free Trial Already a member? Log in Sign up for a free trial and get instant access to this article as well as GBA’s complete library of premium articles and construction details. Since 2008, when Carter Scott built a pioneering Massachusetts house that was heated and cooled by just two ductless minisplits, GBA has endeavored to publish reports from the field to guide people designing homes that are heated and cooled by ductless minisplits. We’ve learned a lot on this topic since 2008.My article on Carter Scott’s approach to heating and cooling was called “Just Two Minisplits Heat and Cool the Whole House.” Since that article was published, builders, engineers, and researchers have shared their minisplit experience and data. Carter Scott has given technical presentations at several conferences (including the Westford Symposium on Building Science and NESEA’s BuildingEnergy conference); energy consultant Marc Rosenbaum has written several valuable articles on the topic for GBA (including “Minisplit Heat Pumps and Zero-Net-Energy Homes” and “Practical Design Advice for Zero-Net-Energy Homes”); and researchers Kohta Ueno and Honorata Loomis have published useful monitoring data (“Long-Term Monitoring of Mini-Split Ductless Heat Pumps in the Northeast”).We now have enough information on the use of ductless minisplits to heat and cool cold-climate homes to set out some rules of thumb. The nine rules of thumb that I present below are based on the work of Scott, Rosenbaum, Ueno, and Loomis, to whom I am indebted. 1. Design your building to have an excellent thermal envelope If you want to heat and cool your building with just one or two point-source heaters, you want an above-average thermal envelope. That means that the building needs a very low rate of air leakage; above-code levels of insulation; and high-performance windows. 2. Consider snow loads when placing outdoor units If you live in snow country, your outdoor unit needs to be protected by a roof — but not a roof that inhibits… center_img This article is only available to GBA Prime Memberslast_img read more

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Solar Panels Don’t Make Good Roads

first_imgFour years ago, a viral campaign wooed the world with a promise of fighting climate change and jump-starting the economy by replacing tarmac on the world’s roads with solar panels. The bold idea has undergone some road testing since then. The first results from preliminary studies have recently come out, and they’re a bit underwhelming. A solar panel lying under a road is at a number of disadvantages. As it’s not at the optimum tilt angle, it’s going to produce less power, and it’s going to be more prone to shading, which is a problem as shade over just 5% of the surface of a panel can reduce power generation by 50%. The panels are also likely to be covered by dirt and dust, and would need far thicker glass than conventional panels to withstand the weight of traffic, which will further limit the light they absorb.RELATED ARTICLESSolar Roads, Pot Growing, Wind Turbines, and Net MeteringAn Introduction to Photovoltaic Systems Because the panels are unable to benefit from air circulation, it’s inevitable that they will heat up more than a rooftop solar panel would. For every 1°C over optimum temperature the panel will lose 0.5% of energy efficiency. As a result, a significant drop in performance for a solar road compared to rooftop solar panels has to be expected. The question is, by how much? And what is the economic cost? The road test results are in One of the first solar roads to be installed is in Tourouvre-au-Perche, France. This road has a maximum power output of 420 kW, covers 2,800 square meters, and cost €5 million to install. This implies a cost of €11,905 ($13,745) per installed kW. While the road is supposed to generate 800 kilowatt hours per day (kWh/day), some recently released data indicates a yield closer to 409 kWh/day, or 150,000 kWh/yr. For an idea of how much this is, the average UK home uses around 10 kWh/day. The road’s capacity factor – which measures the efficiency of the technology by dividing its average power output by its potential maximum power output – is just 4%. The solar road is unveiled in Tourouvre au Perche. Christophe Petit Tesson/EPA In contrast, the Cestas solar plant near Bordeaux, which features rows of solar panels carefully angled towards the sun, has a maximum power output of 300,000 kW and a capacity factor of 14%. And at a cost of €360 million ($415.6 million) or €1,200 ($1,385) per installed kW, one-tenth the cost of our solar roadway, it generates three times more power. In America, a company called Solar Roadways has developed a smart highway with solar panels, including sensors and LED lights to display traffic warnings about any upcoming hazards, such as a deer. It also has heating pads to melt snow in winter. Several of their SR3 panels have been installed in a small section of pavement in Sandpoint, Idaho. This is a 13.9-square-meter area, with an installed capacity of 1,529 Kw. The installation cost is given as $48,734, which implies a cost per installed kW of €27,500 ($31,700), more than 20 times higher than the Cestas powerplant. Solar Roadway’s own estimates are that the LED lights would consume 106 MWh per lane mile, with the panels generating 415 MWh – so more than 25% of the useful power is consumed by the LEDs. This would reduce performance even further. The heating plates are also quoted as drawing 2.28 MW per lane mile, so running them for just six days would cancel out any net gain from the solar panels. And this is before we look at the actual data from the Sandpoint installation, which generated 52,397 kWh in 6 months, or 104,800 kWh over a year. From this we can estimate a capacity factor of just 0.782%, which is 20 times less efficient than the Cestas power plant. That said, it should be pointed out that this panel is in a town square. If there is one thing we can conclude, it’s that a section of pavement surrounded by buildings in a snowy northern town is not the best place to locate a solar installation. However, perhaps there’s a bigger point: solar roads on city streets are just not a great idea. Running out of road Roads don’t actually represent as large an area as we assume. The UK department of transport gives a breakdown of the length of the UK’s different road types. Assuming we can clad these in solar panels, four lanes of every motorway, two lanes on the A & B roads and half a lane for C & U roads (a lot are single track roads and just won’t be suitable), we come up with a surface area of 2 billion square meters. Which sounds like a lot, until you realize that buildings in the UK’s urban areas occupy an area of 17.6 billion square meters. So just covering a fraction of the UK’s rooftops with solar panels would immediately yield more power than putting them on roads. That’s quite apart from the benefits that a more elevated position would yield for greater power generation. All of this suggests that only a small fraction of the road network would actually be suitable. And, given the relatively small size of the road network, solar roads could only ever become a niche source of power and never the shortcut to our future energy supply.   Dylan Ryan is a lecturer in mechanical and energy engineering at Scotland’s Edinburgh Napier University. This post originally appeared at The Conversation.last_img read more

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UK riots: Losses estimated at around 100 million pounds

first_imgStores smashed and looted by rampaging mobs, buildings in flames – the damage was to London and other English cities, but the images were beamed around the world.Four days of riots have already cost businesses and insurers hundreds of millions of dollars. The cost to Britain’s reputation – and its lucrative tourist trade in the run-up to the 2012 Olympic Games – may be incalculable.London’s historic centre, visited by millions of tourists a year, has been almost untouched by the riots which hit a handful of inner-city and suburban areas. That hasn’t stopped images of flaming buildings and shattered shops under headlines like “London’s burning” flashing around the globe.”People read that there are riots in London, they think people are rioting on Tower Bridge or in front of Parliament,” said Tom Rees, senior travel and tourism analyst at market research firm Mintel.”The impression people are getting in other countries is that a lawless state existed in London for a few days,” he added. “The impression could be fostered that it’s just not safe, and that’s a tremendous problem for tourism.”So far there is little hard data, but Rees said there are anecdotal reports about people cancelling trips to London.”I think there is certainly going to be a damaging short-term impact on arrivals,” he said.Patricia Yates of Visit Britain said tourism businesses had seen “concern from some consumers” but not yet cancellations.Most tourist attractions have been unaffected by the rioting. Museums, art galleries, and West End theatres have remained open – though several smaller theatres in riot-hit London neighbourhoods cancelled performances on Tuesday.advertisementThe sports industry has been hit, with a soccer match scheduled for Wednesday between England and the Netherlands at London’s Wembley stadium cancelled to free up police officers for riot duty. Britain’s soccer authorities said they were in talks with police to see whether this weekend’s season-opening matches of the Premier League could still go ahead in London.Tom Jenkins, chief executive of the European Tour Operators Association, said the images of riots looked bad, but the disturbances would have little long-term impact on Britain’s resilient tourism industry.”My members move tens of thousands of visitors in London every day and I haven’t had any reports of anyone being caught up in it,” he said.”We’ve had major terrorist bombings, we’ve had sustained IRA campaign, we’ve had riots before. London is one of the most vibrant and safest places a tourist could go to. And that remains the case.”Aside from the impact on tourism, the riots have hurt a huge range of British businesses, big and small.The looters’ targets ranged from corner stores, stripped of booze, cigarettes and candy, to chains selling youth-friendly gear such as sportswear retailer JD Sports, music-seller HMV.A huge warehouse in north London owned by Sony Corp. subsidiary Sony DADC was torched on Monday, destroying thousands of computer games, DVDs and CDs – including the stock of a distributor for dozens of independent music labels.Domino, one of the labels affected, said the new single by British band Arctic Monkeys will only be available for download only because it has no physical copies to ship to stores.Colin Stanbridge, chief executive of the London Chambers of Commerce and Industry, said the riots could not have come at a worse time – less than a year ahead of the 2012 Olympics and with Britain’s economy still fragile after a prolonged recession.”At a time when the capital’s businesses should be focusing on growth and job creation, the riots have prevented them from going about their day-to-day business,” he said. “Many firms have had to put contingency plans in place, with some forced to close early in order to save their property from possible criminal damage.”The Association of British Insurers says insurance companies are expecting losses of “well over” 100 million pounds ($160 million) from the mayhem, although Rolf Tanner, spokesman for insurance giant Swiss Reinsurance Company, said all estimates of the cost of the damage are premature.”The unrest has so far hit mainly the poorer areas of London and other cities, where insurance density and insured values tend to be lower than the country average,” he said.Most retailers hit by looting will be covered by insurance policies, but James Lowman, chief executive of the Association of Convenience Stores, said some small shopkeepers “might be uninsured or underinsured.”He said those retailers can use a piece of 19th-century legislation called the Riot Damages Act to claim money back from the police for failing to protect them – but only if they apply within 14 days. Lowman said his association was trying to get the government to extend that period.advertisementHe is more worried about the long-term effect on small businesses, should trouble and fear persist.On Tuesday stores in many parts of London closed early or even boarded up their windows from fear of violence that never materialized.Lowman said that trade from shutdowns can’t be claimed back from insurers. And small stores can’t afford the private security guards employed by larger retailers.”In Northern Ireland, which had trouble with riots for many years, there is evidence there that sometimes retailers just give up,” Lowman said. “And that’s tragic.”last_img read more

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