In ‘Solar Hot Water’ Category
From the archive: Use the sun to heat the house
In ReNew 116 we look at a variety of hydronic-based heating systems. In this article from ReNew 95, Michael Harris gives a good overview of hydronic space heating systems that use evacuated tube collectors for solar boosting. We hope it gives good background to the hydronic heating feature in ReNew 116.
The idea of using the sun to provide heating for your house is very attractive. In the southern states of Australia space heating is the biggest energy user and in country properties heating can be very expensive if you are using bottled gas and hard work if you are using firewood. Solar energy is free, and produces no greenhouse gases. It could be a great solution.
READ MORE »The increasing use of hydronic heating has the potential to make solar heating easier. Hydronic heating systems distribute heat through a house by running hot water through pipes to radiators in each room or to coils in the concrete slab. It is easy to shut down the radiators or coils that you do not need and the system can be quite efficient. The water can be heated by a gas or wood-fired boiler or by solar.
So the solution to your heating needs sounds simple. Put in a hydronic heating system and bung some extra solar panels on the roof. Whoopee, we have solar heating. However, unfortunately it is not that easy.
For many years solar water heating in Australia has been done by using flat plate collectors. These collectors are basically an insulated box with a glass top and a sheet of metal with pipes attached inside the box. The sun shines, the inside of the box gets hot, the sheet of metal gets hot and the pipes containing the water get hot. It works well when it is sunny.
However it does not work so well in cloudy conditions. And when it is winter and it’s cold, when you need the system to perform at its best, these collectors provide very little energy input. Although the flat plate collectors would give you some benefit, the cost of the extra collectors far outweighs the benefits.
So what has changed?
Affordable evacuated tube-based collectors have come onto the Australian market. These work differently to flat plate collectors and are much more efficient in cold and cloudy conditions. The tubes have a double glass wall like a thermos flask. In between the two walls is a vacuum which is an excellent insulator and minimises heat loss. On the outer wall of the inside tube is a selective surface which maximises the absorption of solar radiation. When faced north the curved outer surface of the tubes will effectively collect heat from the sun at all times of the day because reflection off the glass surface is minimised.
So you end up with a number of benefits; a selective surface that absorbs more heat, a vacuum that stops that heat escaping and a round surface that reduces reflection hence collecting more heat. The result is a solar panel that collects more heat, especially in winter.
How it works
At the time of writing, one green plumber had been installing systems using the Sunplus CPC Solar brand of evacuated tubes. The typical system consists of eight 12 tube panels, a 1200 litre stainless steel tank with two heat exchange coils, a controller and solar circulator pump, mixing valves, expansion tank, a combination boiler to back up the system, and the components for the hydronic system (pipes, pump, valves and radiators or floor coils). A system of this size would be capable of heating a 25 square house.
When operating, the sun heats the water in the pipes in the evacuated tubes. A sensor detects when the water reaches the appropriate temperature and switches on the circulation pump. The pump circulates hot water to the heat exchange coil in the bottom of the storage tank. As the water heats up it expands and pressure in the circuit builds up. Rather than vent the pressurised hot water (which would waste water) the pressure is taken up by the expansion tank.
A coil in the top of the tank heats up with the water in the tank. When the pump for the hydronic heating system is turned on, heat is transferred to the water circulating around the hydronic heating circuit. If the solar system does not heat the water in the hydronic loop adequately, the boiler comes on and boosts the temperature. Domestic hot water for general household use can be heated by a separate heat exchange coil in the tank.
A critical aspect of the system is the mixing valves. The evacuated tubes are capable of generating high temperatures. Reliably regulating these temperatures is essential for both safety and reliability reasons. Boiling water can burn someone who touches a radiator, crack a concrete slab with embedded heating coils, or kill the boiler that boosts your system.
What does it cost?
Hydronic heating systems are not cheap. As a rule of thumb, the cost per radiator (including piping) is about $1000. The alternative, an in-slab floor coil, can be around $4500.
The solar components to heat a 25 square house would work out something like this; evacuated tubes $9000, custom-built tank with coils $4500, and combination boiler $2500. Installation and miscellaneous hardware add about $2500. So you can be looking at total costs for the hydronic heating of between $6000 and $10,000, and the solar heating system could be close to $19,000.
Some government rebates also apply to these systems. The solar heating system above would receive a $1500 rebate in Victoria, bringing the cost down to around $17,500.
Although this is quite a lot, remember that these systems also supply domestic hot water. A solar water heater typically costs around $5000 so the actual additional cost for the solar boosting of the heating system may only be around $12,500.
Savings
So is it worth it? To answer that, you need to take into account the life of the system. The chief cost components—the evacuated tubes, tank and piping—should have a very long life, 20 to 30 years would not be unreasonable. The pumps and valves may need replacing during that time but they are a relatively small part of the cost.
Running a hydronic heating system such as this would be likely to cost around $600 per annum in the city or about $1700 per annum in the country using bottled gas. This means the heating costs over 20 years in the city would be $12,000. In the country it would $34,000.
If the solar boosting provided half of the hot water needs then it would save $8000 in the city and $22,644 in the country. The savings are even greater when you add the domestic hot water savings and take into account the likely increases in energy costs over the next 20 years.
Performance
These systems are new in Australia so there has not been enough time to see if they will deliver what they suggest. But the results look promising. Lets look at the experience of some people who have put these systems into their homes.
Gordon, from Arthur’s Creek in Victoria, has installed a system with 15 panels of six tubes each, connected to a 1100 litre storage tank. Last winter his gas boiler was consuming two bottles of gas every five days, at a cost of $160! ‘When we realised how much it was costing us to run our heating we stopped using it. We only turned on the heating when we were desperate.’
Gordon’s new system was installed last spring so it has not yet had the chance to run through a winter. But based on how it’s been performing it looks promising. ‘The system started to operate in spring when the daily top temperature was typically 18 to 20 degrees. On the first day the tank temperature went from 15 to 45 degrees and within a few days was over 80 degrees and went off scale on the temperature gauge. Ever since it has been boiling and sitting at close to 100 degrees Celcius.’
Mitch from Seymour has put in a system to assist the heating of his 65 square house. He was first inspired by an item in ReNew on evacuated tubes. Later he was staying in South Georgia (near the Falkland Islands) and was astonished to see the very same evacuated tubes on the British Antarctic Service buildings. South Georgia is close to the Antarctic and experiences very low temperatures and strong cold winds. Mitch reasoned that if these evacuated tubes worked there, they would certainly work in central Victoria. His system uses 18 six-tube panels, storage tanks with a capacity of 1,400 litres and a combination of floor coils and radiators to heat the house.
Glen from Greendale installed a small system with six panels with six tubes each, and an 880 litre tank. Glen wanted to test his system performance so he installed sensors in the tank and panels. The system was installed in September and was providing plenty of hot water for domestic use, (the hydronic system was not being used because it was summer).
During Christmas Glen went away on holiday. When he came back the system was not working. He checked and found the sensor in the tank had melted and popped out of the tank and the collector sensor had not only failed but the heat shrink on it had melted off. He has since killed several more sensors while playing around to see what temperatures he could get from the system.
While the thermal performance of evacuated tubes in cold conditions and low light conditions suggests that these collectors may make solar hydronic heating a viable option, we will need to see how these systems perform through a full winter. It is not hard to get hot water in summer—winter is the real test.
It is also important to remember hydronic heating systems need to be installed by an experienced professional and adding a solar component increases the complexity of the system. Readers thinking about trying this kind of system should be cautious and do their homework.
This article was first published in ReNew 95
Farmhouse solar hydronics
In issue 116 we visit Ian Hill’s 1970s home which has been retrofitted with solar-powered water and household heating. Here’s is a detailed version of that article, with more of the nitty gritty on system design for those about to embark on such a project.
Nearly nine years ago we made a tree change to active, semi-retirement. We bought a farm in West Gippsland, left behind seaside Frankston, and went niche beef farming for a change in lifestyle. We’re happy to say it was a good decision.
READ MORE »The farm came with a large home—16 rooms over five levels with two open-plan living and entertaining areas—the main selling point being we liked this style years ago.
The three concrete slabs stepping down the rolling red soil hills already had hydronic in-slab tubing, heated from a diesel furnace along with the tap water. Cooking was done by bottled gas, and there were three slow-combustion wood heaters in the two living areas.
Philosophy and design
We are very keen on sustainability and want to minimise our carbon footprint, both in the home and our farm’s beef production. We were prepared to spend some money converting the heating system for a large reduction in running costs and emissions. The farm has many large trees and limbs are always falling, so using solar-powered heating and hot water, boosted by a wood-fired heater, seemed like a sensible idea.
We found the solar collectors we wanted and set system parameters. Our plumber designed and built the conversion, changed the skylights, re-flashed the house and updated much of the water collection. We added ideas as it was built over several months.
The home
The climate is cool temperate with few frosts and the house is sited on a southern slope in foothills.
We are at latitude 38.005°. There is some unavoidable morning shading in winter from a roadside glider possum habitat of magnificent eucalypt trees over 40 meters high, 30 meters away and uphill on the northern road boundary. The outside temperature ranges between 2°C and 42°C but the house has such a large thermal time constant that living areas stay between 17°C and 22°C in winter, and no more than 25°C after a run of hot days.
The house design is classic 1970s double brick with rough-sawn, exposed beams in eight meter cathedral ceilings.It had hardwood french and other windows with single-glazing throughout, and sad plastic-vented skylights. Everything was coloured mission brown.
The designer ignored the 16 kilometre view to the Strzelecki Ranges and the valley below, and modern principles of house alignment for passive heating and cooling. However, at least the sun does not load up the interior. There are a few, small windows to the east, with excellent shading from canvas blinds, and large french windows to the west. These are shaded by a pergola and close battens. The home’s north face is stepped into the hill and the windows are totally shaded by a brick cloister with archways: a very sensible design providing a great spring breakfast area.
The kitchen, living and lounge rooms, study and billiards rooms are open plan and interconnected on three levels, which does create air currents, especially with such high ceilings. We have been slowly renovating, as one does with a retirement income.
The aim is to convert major glass in living areas to high-efficiency glass and to install as much double glazing as we can afford. So far our plumber has retrofitted seven double-glazed, openable skylights. The local glazier replaced 11 clearstory windows and made three panels openable to draw up cooling air from the lower levels when a summer cool change arrives.
We use pressurised tank water for most of the home, buildings and farm animals. There are 245,000 litres available in concrete tanks, linked by a 50mm buried ring main. Our local irrigation contractor built a fire sprinkler system for all buildings on the farm, which was essential when the wind changed during the Black Saturday bushfires in 2009. Our 100-year average rainfall is 1100mm; we received 1178mm in 2010 so we always have an excess of stored water.
There is a 1.5kW solar power system on the roof, bringing an income and well offsetting the minor energy drain from the small pumps moving water into the hydronic heating and up to the solar collectors.
Hydronic system components
Our heating system has three sources of heat:
• 36 solar-collecting vacuum tubes (rated at 5.8kW)
• wood-fired, slow combustion fire, with flue water jacket
• two gas-fired instantaneous hot water boilers.
The service courtyard where most of this hybrid heating and hot water system is hidden looks Heath Robinson, but it is a credit to our local green-accredited plumber at Baw Baw Plumbing and his team. He always knows about the latest efficiency innovations and was a terrific speaker at our Landcare group’s Green Energy field day.
Heat storage
A custom made 1000 litre stainless steel tank with 75mm of insulation and a small header tank is the heat storage. It’s similar to those made for the local dairy industry. Hot water is not drawn from this water but via three heat exchanger coils in the tank, with the solar one at the base, the hydronics one at the centre and the hot water service at the top. Each is 11 metres long.
Solar collectors
I contacted eight retailers advertising evacuated tubes. Disappointingly, not many responded.
From sellers’ claims, the most efficient collectors I could find were Ritter (labelled APR), a Chinese-made German design imported by Sunplus CPC. We bought 1.6m long evacuated tubes in banks of six, with parabolic mirrors to direct extra sunlight under the tubes. Our budget limited us to triple the normal number of tubes recommended for hot tap water and a 1000 litre hot water storage tank.
The collector bank of 36 tubes is fixed to a 1.6m by 4.4m aluminium frame facing 15° west of north. I asked for it to be tilted steeper than the roof’s 17° at a calculated winter solstice angle of 60° to collect maximum energy for winter. This reduces excess summer yield and steam problems.
Importantly, the plumbing route for the tubes allows us to add more down the track.
The north roof with evacuated tube collectors for the heating system and a 1.5kW solar power system.
Inside the solar control and storage area
Solar-heated water pumping
This is a rainwater-filled closed loop heat-exchanger. Water from the storage tank coil is lifted about five metres up to the solar array by a 3-speed 30 watt 240v hot water pump with throttling valve, giving infinitely variable flow. It usually runs at 0.2 bar boost. A Zilmet model 20013 50 litre cylinder stores system over-pressure up to four bar from summer days, backed up by a blow-off valve to save water loss on hot days.
Relief valves
Four high spots in the solar array and wood heater circuits have auto air-bleed valves, allowing only air and steam to escape.
Wood-fired slow combustion heater
We changed the third wood heater to a gas unit for quick response to a cold home.
After the first winter with the new system, an existing free-standing Saxon unit in the living room was retrofitted with a 550mm tall stainless steel heat exchanger in the first part of the flue. It burns quietly from late autumn to early spring on wind-fallen mountain ash and blackwood harvested around the farm. Water to the flue exchanger is drawn from the base of the storage tank and delivered back to the top. Piping is about 25 metres long and rises about 3 metres. It is insulated with 25mm thick foam tubing and cased in colorbond. A 240v thermostat in the output pipe in a wall behind the heater senses output temperature and controls another small circulating pump at the storage tank, moving two litre slugs of hot water at 50 °C into the storage tank every few minutes. This heater provides around half our total hydronic heating in winter.
Gas boilers
Tap water is delivered via an instantaneous Rinnai V1500 gas boiler which adds heat if stored water is not 50°C. There are no adjustments for the home owner. Electronics in this unit can be damaged by our emergency home generator, so we cannot run the hot water when mains power fails, which it does for several hours at least four times per year.
Hydronic water supply is delivered to the mixing valve via a Sime Format 34e instantaneous gas boiler, rated at 11.2kW to 34kW, large enough to heat the whole home on its own. It adds heat if needed and has user-adjustments for output temp (set to 35°C). Its instruments display output temperature and pressure. The pump within this unit is also triggered by the thermostat in the master bathroom, sending heated water to a Hydrotherm P-600 Platinum tower rail, 2.2m by 600mm wide, helping provide some extra hydronic heating to the bathroom.
Both boilers stay on in summer as they do not use any gas unless heating water.
Heat users
The house is heated by hydronic coils in five zones in three concrete slabs at descending levels in the house, plus a fan-assisted radiator in the living room. Two manifolds are fed from a mixing valve, and water circulated by five, 240v Grunfos thermostatically-controlled 3-speed pumps.
We have only activated the outer coil on the lower slab coils. We are very fortunate that it flows via the master toilet and bathroom, laundry, kitchen, two guest bedrooms and to the living room on the lowest slab.
Hot tap water runs throughout the house with all piping insulated with 25mm thick foam tubing. External piping is further encased in 90mm stormwater piping.
Water delivery controls
Hydronic water is blended by the original tempering valve supplying two hydronic manifolds. Tap water is held to 50°C by a Reliance Heatguard Ultra tempering valve. This setting can be altered.
The three room thermostats in the home are very clever Honeywell model CM 907. They can be programmed in time blocks for every day of the week, can be over-ridden for one time block, set to a fixed temperature and adjusted for daylight savings. The lower slab thermostat in the living area also masters the upper slab in the entertainment area. The second thermostat in the upper level study controls the mid slab. The third thermostat in the master bathroom controls water to the towel rail.
Operation
Solar control
The electronic differential controller, made by Whitnic Services of NSW, gets its data from 10volt thermistors, one at the array output and one at the storage tank top. It has three modes and a red light indicates the pump is on, which I positioned to see from the back door.
Gas supply
Gas was originally supplied by a bank of 40kg cylinders. These were replaced by a 190kg truck-filled tank, with pressure reducers at two boilers, and a circuit supplying the guest kitchen and fast-response gas heater in the living room.
Owner adjustments and monitoring
I wanted to monitor input and tank temperatures, so I bought three $10 electronic indoor/outdoor thermometers with remote sensors and mounted them next to the differential controller. I can feel the input arriving from the solar array, with one attached to the lowest hot connection on the storage tank, indicating roughly how much hot water is in the tank, and the other reads water delivery to the taps. These have max/min displays as well, useful for checking array performance or pump adjustments. An old clock-type dial indicator measures the temperature of water returning from the hydronic system, a rough indication of how much heat is in the slabs.
The electronic gauges are particularly useful to know how much heated water is available for a big load such as a spa fill or running the lounge room radiator. Monitoring incoming temperatures from the array allows me to tune up the flow rate for best performance just below steam occurring, and tells me if we have any problems when it’s pumping. An improvement would be digital readings from the differential controller’s thermistors.
We can adjust slab heating times in two zones and towel rail temperature, and boost heat in the lounge room by activating the fan-assisted radiator. We can control the temperature of the water leaving the fire water jacket. We cannot alter the temperature trigger points for the solar array. It might be useful to keep it pumping above 80°C to stop a steam blockage occurring.
Current settings
Thermostats have six available time block settings, with the initial settings for the slab thermostats listed below:
TIME TARGET TEMP
6am 20°C
8 18°C
Midday 18°C
5.30pm 18°C
8.40pm 13°C
10.30pm 8°C
When there’s a run of low solar-energy days we run the wood fire hotter. When there’s sunny days predicted, we can use less wood, or not light it.
As autumn starts, we open the hydronic valves and drive the wood heater hard to put as much heat as possible into selected slabs prior to cold snaps and overcast winter days. On a run of overcast days we open the damper on the wood heater.
Fine tuning and problems
We run the collector pump at the lowest of three speeds and fine-tuned the flow to 1.5l/min on the advice of the plumber. We’ve learnt that in summer we need to double the flow rate to avoid excessive pressure build-up.
The original thermistor on the solar array burnt out after one year and the surrounding insulation was charred! The new importer tells me the replacement thermistor is a tougher type.
Anything that stops the circulating pump while there’s sun on the vacuum tubes can create a blockage in the circuit that the circulating pump cannot overcome. When the thermistor on the roof fried, and when we lose power when the sun’s on the tubes, pressure builds up and the closed loop finally drops below it’s 0.2 bar pre-set pressure. This stops circulation for that day and we lose a little water as steam. When the pump is alive again it fails to get water circulating if the array is in sun. So if the system pressure gauge is zero, I know circulation has stopped and must be topped up. To fix it we fit the garden hose onto the fill point just below the pump, and run cold water until there are no bubbles passing the sight gauge. Our plumber has suggested an automatic supply for this.
Maintenance
Particle filters in the inlets to the tap boiler and both tempering/mixing valves need to be cleaned annually, the latter by removing the fitting gland, which is not a good design.
The Zilmet pressure storage tank needs its quiescent air pressure checked annually, and the whole tank replaced every five years. Pressure cylinders on my Citroen last indefinitely, with re-gassing, so we’ll see. The system needs to be de-pressured for accurate pressure checks.
The solar collector array needs to be hosed periodically to remove leaves.
Costs
Our gas costs about $730 for 550 litres per year, but my urban mate pays a fraction of our price! We really only use significant gas when we have guests, then it goes through the litres when the large boiler is doing a lot of the home heating. We average about 66 mjoules of gas per day in winter, and as little as 19 at other times. The Elgas truck doesn’t come from October to late April. In 2010 we used half the gas of 2009, mainly due to better windows and remembering to keep bedroom doors closed. We will get further significant reductions when our window conversions and internal glass partition are finished.
Total changeover cost, including towel rail and some bathroom alterations, was about $11,500 against an estimated $17,000. The local shire gave us a rebate of $250 and we received another $6900 in rebates. If hydronic slab heating was built into a new home, it may not be any more than other hot water and heating systems. Our 44 RECs were not sold because the supplier did not have an approved system with the tank size we used, so we missed out on around $1500. That’s a little plus for the environment as energy companies had to find an extra 44 RECs somewhere else.
Changed family habits
The dog is often asleep on the hottest sections of the hydronic loop, always in doorways or on the top of stairs. The cats love the laundry benches in winter.
To minimise the generation of greenhouse gas and gas bills we use most of our hot water first thing in the morning, giving the solar array the first opportunity to recover hot water lost. We built a wooden, pull-down rack below the laundry ceiling which now dries much of our cold weather washing.
We need to shut off the hydronic valve when spring is well-entrenched and must remember to open it when the first cool weather is predicted after Easter.
What next?
We are part-way through replacing most open-plan area windows with double glazing, with low U and SHGC value glass and argon gas in the space.
At the moment glaziers are installing a glass, openable air barrier at the top of the living area. This will zone the home into separate living and entertaining zones, reducing wood demands and cold air currents up the kitchen.
Stopping heat escaping is next. After a government-funded home assessment, this air entrapment work was to be financed by the now defunct Green Loans scheme. Another task is resealing all doors, and chasing air leaks along the brick-ceiling interfaces throughout the living spaces and external walls. This is to stop bushfire embers and smoke ingress; the home is to be a refuge as we’ve spent a lot of money on a 10-hour fire sprinkler system for all buildings.
I’m also planning to have the roof re-pointed; it’s amazing how much heat escapes from the fabric of the cathedral ceiling when you remove a capping tile on a cold day.
Much of the living room slab could be heated, in cooler weather, by direct sunlight, and possible when we replace dark green fibreglass on the pergola outside with clear sheets and retractable shade cloth.
I’d like an automatic system to over-ride the pump control in the main gas boiler, so the rail can be heated when the slab hydronics are off. This will probably involve some extra 240v relays to override the pump’s under-temperature and gas supply controls, which stop the pump when the hydronics are not on.
Due to firebox corrosion we will soon replace the wood heater. The next one will have a wet-back for more hydronic capability.
Suppliers
Green-accredited plumbers—Baw Baw Plumbing, Buln Buln East
Solar equipment suppliers—Phazer, Warragul
Glaziers—Walkies’s windows and glazing, and Warragul glass and glazing
Flue heat exchanger, gas room heater—Cosy heaters, Warragul
Monitoring thermometers—Dahlsens, Warragul
Fire protection system—The Farm Depot, Warragul
Gas heater installation—West Gippsland gas services, Warragul
Solar hot water for small spaces
This product review is from ReNew 115. Check out more products here
READ MORE »Most evacuated tube solar hot water collectors use tubes at least 1700mm long. For installations where there isn’t much roof vertical space or where the panel needs to thermosyphon to a tank mounted low in the roof cavity, standard tubes are too long.
The Solarvox SVM30-58/850 and SVM35-58/850 systems consists of 30 or 35 evacuated tubes respectively. Each tube measures 58mm diameter and is just 850mm long. This results in a collector that is short but wide, making for a more flexible range of installation options.
The Solarvox systems can be mounted on balconies and even above windows, taking the place of eaves or awnings, so the collector can double as both hot water system and sunshade.
The collectors are suitable for thermosyphon as well as pumped systems and a complete 30 tube collector weighs 55kg. The tubes have passed a 25mm hail test and the collectors are designed to continue to collect heat even when missing some tubes.
RRP: $1080 for the 30 tube collector, $1280 for the 35 tube. Delivery is available, but pickup from Fairfield, VIC, is recommended.
For more information contact Solarvox, ph: 0417 591 463, solarvox@gmail.com, www.solarvox.com.au
Household Renewable Energy and Natural Disasters
Natural disasters seem to be an increasing part of life. Whether floods, cyclones, bushfires or earthquakes, our world is becoming a more unstable place.
READ MORE »The latest issue of ReNew magazine takes a comprehensive look at what to do before, after and during a natural disaster to protect a renewable energy system.
Solar panels, water tanks and wind turbines are just as vulnerable as other technology in the face of nature, but steps can be taken to keep them safe:
Solar panels
- Turn off mains isolator in meter box
- Turn off DC input to inverter
Water tanks
- Choose a tank material suitable for your climate, like steel or concrete for bushfire-prone areas
- Secure tanks as well as possible or use underground tanks
Small wind turbines
- Shut down wind turbines if possible
- Lower tilting tower systems to the ground if safe to do so
Battery-based power
- Isolate battery bank
- Turn off the inverter and disconnect any mains connection
Also in the latest issue of ReNew
Re-Use Your Television competition
Houses made from hemp
Double glazing buyers guide
Cubby houses go green
Super-efficient hot water know how
Richard Keech explains how he combined an evacuated tube solar collector and a heat pump to make a high efficiency hybrid water heater.
On my three-bedroom Melbourne house I have what might be the most efficient solar hot water system around. In the year since installation it has performed extremely well, and I’ve learnt a lot along the way. This article will consider aspects of solar hot water design and rationale that led me to the system I have now. Then it will look at the system as built and the lessons after one year of operation. My design for the system brings together some ideas about what makes for a more sustainable hot water system. Some of these ideas challenge conventional wisdom on the subject.
Crank it up
For hot water, the Your Home Technical Manual for example suggests to tilt the (north-facing) solar panels at an angle corresponding to the latitude of the location and “in some cases, it may be desirable to increase the angle somewhat to improve winter performance and reduce overheating in summer”. Despite this, it’s uncommon in my experience to see solar collectors tilted above 35°.
My interpretation of the situation is that it’s more than merely “desirable in some cases”—it’s really important to increase the tilt of solar collectors for hot water, but not PV. To appreciate why, we need to recognise the key difference between solar hot water and solar PV, namely, that solar hot water systems cannot make use of their surplus energy. Indeed excess summertime solar gain can be a problem as discussed in ReNew 113 (DIY Solar Hot Water Cover page 72). On the other hand, urban PV systems have the benefit that excess generation is simply exported to the grid.
Grid-connected PV systems are best configured for maximum annual solar gain. However, we need to apply a different rule of thumb for hot water—to configure for the maximum number of days with sufficient solar gain. This means cranking up the solar collectors to a much steeper angle. This is done to maximise solar gain in winter and to help reduce overheating problems in summer. To optimise for winter noon, the angle should be latitude plus 23.5°, which in Melbourne is 61°. Given that the angle of the sun is lower than its noon angle for most of the daylight hours, it follows that the collector angle should be even a little higher than this. I chose to tilt my collector at 64° from the horizontal.
Read the full article in ReNew 115
Can’t afford a solar hot water system? Try a retrofit kit
Dave Wakeham investigated several solar hot water options before finding that a retrofit kit was the best solution.
I couldn’t help but think there was going to be a big rise in the price of electricity, and as we are on a fixed income (both on disability pensions), I was worried that it was going to blow our budget. I was sure there was a way to beat this.
READ MORE »Our biggest electricity use is an electric hot water system, so I decided to start there. The cost of a close-coupled solar hot water system was about $5,500. Things are quite expensive in North Queensland but I thought this was exorbitant and beyond my means. There was additional expense because my house has an aluminum roof and needed beefing up to take the weight of a close-coupled system with a collector panel and tank.
The plumber said it was not feasible to remove the large sheets of aluminum to add the timber, as it is almost impossible to put them back due to the age of the roof. He suggested that I build a leanto off the side of the house and use the solar collector as a roof for it.
I deliberated for some time (my wife says I normally do), and when the next ReNew magazine arrived I was quite surprised to see there was an in-depth article about solar hot water systems. The article started me thinking that maybe I don’t need a full system. I already have a perfectly good, well-insulated 125 litre electric hot water tank with a good element.
A retrofit seemed to be the way to go. I read about a five-way valve, a 10 watt PV panel, 12 volt pump and a solar collector and fittings. I thought this may not be as expensive as a whole system if I could find the items locally. I investigated and found that people would rather sell me a whole system. Also, a retrofit would not be covered with a warranty and did not attract a government subsidy. Back to the drawing board.
Buying a kit
I then read about a Solar-Mio/Metal Dynamics retrofit kit made by Albury Consolidated Industries. After a few emails to establish exactly what is in the retrofit kit, we decided on a SM-Tops1 squat panel PV pump system with five way fitting at a price that included freight to Townsville. We decided that one panel would be enough as we are a two person household and only use hot water to shower each day. I was extremely happy with the price as it was less than a third of the price of a leading brand close coupled system that sold in Townsville.
Read the full article in ReNew 103.
Solar hot water buyers guide
If your old hot water system has given up the ghost, maybe it’s time to go solar. We show you how solar water heaters and heat pumps work, what’s available and how to choose the one to best suit your needs.
There are many reasons to choose a solar hot water system or heat pump over a conventional gas or electric water heater. With the rapid increase of energy prices in recent months, a solar or heat pump water heater can greatly reduce energy bills. Up to 30 per cent of household energy is used just to heat water, so anything that can reduce this energy use will save you a lot of money.
READ MORE »Another important benefit of such a system is that of greenhouse gas emission reduction. A solar water heater or heat pump can reduce the greenhouse emissions of an average family by as much as four tonnes of CO2 per year—the equivalent of taking a car off the road!
Most state governments have recognised the advantages of solar and heat pump water heaters and offer incentives in the form of rebates. These vary from state to state, but can save you a great deal on the cost of a new water heater, making them more economically viable. The initial purchase price will probably still be higher than a similarly sized conventional water heater but the savings made in running costs will pay for this difference in less than 10 years—in as few as four years in some cases.
How does it work?
A solar hot water system usually consists of a hot water storage tank connected via pipework to solar collector panels. These collector panels are placed on a north facing roof and at an angle of no less than 15° to the horizontal. The tank can either be situated immediately above the panels on the roof (called a close coupled system), above and a small distance away from the panels within the roof cavity, or at ground level (a split system), in which case a pump and controller is required to circulate water through the panels.
As the sun shines on the collector panel(s) the water in the pipes inside the collectors becomes hot. This heated water rises through the panel and out through a pipe to the insulated storage tank. Cooler water from the bottom of the storage tank enters the panel at the bottom to replace the warmer water.
This is called the thermosyphon process, requires no pumps or other devices and is very simple and effective. However, it does require that the storage tank be situated above the collector panels. The collector panel is the driving force for the circulation, so due care must be taken with its mounting and orientation to get maximum benefit from it.
If the tank cannot be located above the collectors, a pump and a differential temperature controller must be used to provide water circulation. The controller also turns the pump on when the temperature drops to 5°C as a frost protection function.
Some systems don’t heat the water directly but instead heat a fluid similar to antifreeze used in vehicle cooling systems. This fluid flows through a closed loop system (through thermosyphon or pump action) and transfers the collected heat to the water in the tank via a heat exchanger.
There are pros and cons with each system. Close coupled systems require the roof support the full weight of the tank, but they are much simpler than split systems and little maintenance is required.
Split systems have a much slimmer roof profile and are more convenient should tank maintenance be required, but the added complexity of the pump and controller means that failures tend to be more common.
Read the full article, including tables with details on sizes and prices, in ReNew 114.
Eureka! From coal to solar
One clever Latrobe Valley enterprise is helping workers switch to low carbon employment, writes Sasha Shtargot.
Drive east out of smog-bound Melbourne along the Princes Highway and before long you are in the haze that perpetually sits in the Latrobe Valley.
Pitted with brown coal mines, the valley has long been in the firing line as the dirty heart of Victoria’s power generation system. It is home to Hazelwood, the most polluting power station in Australia, pumping out over 16 million tonnes of greenhouse gases each year.
Yet the area that has long depended on jobs from brown coal has started heading in the opposite direction—towards a manufacturing base in clean technology. More precisely, the making of solar hot water units.
Eureka’s Future, a co-operatively run factory, is set to start operating next year with 50 workers in Morwell. With the support of Dandenong manufacturer Everlast and Douglas Solar, it will produce stainless steel tanks with Solar Mio flatplate collectors, Grundfos pumps and Bosch boosters. By the end of 2011, it is expected to be making 500 solar hot water units a month. With rebates and including installation, a Eureka’s Future gas-boosted tank will cost country homeowners $2655 and city dwellers $2755. And it will come with a 10-year guarantee.
DIY floor heating, and it’s solar!
A heated floor can be just the tonic in winter. Per-Steinar Jacobsen shows how he installed his own solar hydronic floor heating.
I have long been an advocate of renewable sources of energy such as solar and wind power. In the mid seventies I built a house in Hahndorf, South Australia, where I installed underfloor heating, radiators and a central heating boiler. I made provision to connect solar panels to the boiler when I had the money to do so.
READ MORE »Renewable energy is just as important with the house that my wife and I are currently building in Port Germein. However, the renewable energy features have been installed from the very beginning, including the solar hydronic underfloor heating. Here’s how I did it myself.
To start off, I searched the internet for evacuated tube solar collectors. I found some in America which were reasonably priced; interestingly they were used for space heating as well as for hot water. I investigated transportation costs to reflect the true cost of buying from overseas.
In the end I decided to buy them locally from Sunplus CPC Solar in Victoria. I purchased a retrofit (conversion) kit containing four 12-tube collectors. With this kit came three pumps, two temperature pump controllers and some plumbing hardware. This was the easy part, now I had to decide on storage tanks.
Again I searched the internet for suitable hot water tanks. A local hardware store had some 315 litre tanks in stock. I took the model number, rang the factory in Sydney and asked whether it had internal heat exchanger coils. The answer was ‘yes, all our tanks have internal coils,’ so I bought this $1,000 tank, only to find out later that there were no internal coils in this tank. So much for correct information from the manufacturers!
Read the full article in ReNew 104