Tweaking an Solar Hot Water (SHW) System

An amazing article that we saw in "Home Power Magazine", Enjoy it.

Two situations: 

I recently had a solar hot water (SHW) system installed on my house. It is a closed-loop, evacuated-tube system with a heat exchanger in the storage tank. The differential control (a Caleffi Solar Plus) provides variable pump speed control. Currently, it is using factory defaults for the conditions that determine pump speed. The system has four temperature sensors and a data logger, which help me keep tabs on its function.
I like the idea of a variable-speed pump because it seems like it can add efficiency to an SHW system—just like an MPPT controller does to solar-electric systems. That said, I am not sure what conditions drive the efficiency of the SHW system. Should the control be set for lower flows and higher temperatures, or higher flows and lower temperatures? I know there is more heat transfer at the exchanger with a higher temperature difference between the transfer fluid and tank water, but I am not sure how that balances with the collectors’ lower efficiencies at higher temperatures.
Is there a reference I can use to figure this out? I am not looking for specific numbers—more like basic explanations of relationships between the parts of the system and what to look for as a sign of how well an SHW system is performing. Perhaps it’s something like checking transfer-fluid temperature drop across the heat exchanger versus the temperature rise at the collector.

Jack Herndon • Seattle, Washington

An ideal collector loop of any SHW system would operate at a difference in temperature of just a few degrees between the inlet and outlet temperatures of the collectors. The higher this differential, the more heat is lost to the outside atmosphere.
This loss is dependent on the outside temperature. Although evacuated tubes are more resistant to heat loss, they are not immune to it. If you’re seeing a temperature difference of 50°F or greater, your system is suffering from a low flow rate problem. A system with a 20°F difference is much closer to operating at an “ideal” temperature.
The ideal is a compromise between the lower inlet/outlet differential to minimize heat loss, and a high-enough differential to prevent the control from short-cycling. Short-cycling will occur with too high of a flow rate and will be noticeable—the system will turning on and off excessively. Turning on and off is normal in the early morning and late afternoon and in cloudy weather, but shouldn’t happen in mid- day bright sun.
Chuck Marken • Home Power solar thermal editor

The Answer: 



Thermostat Dilemma
Is it more energy efficient to turn off your home’s heat when you’re going to be gone all day, or to leave it at a slightly lowered set point? I realize that this is likely a complex calculation involving volume of space, outside temperatures, building envelope and insulation, number of degrees in drop and recovery, elapsed time, type and cost of heating fuel, etc. But perhaps there are some general rules or simplified formulas that can direct a homeowner on the best approach.


Temperature Differentials, With & Without Heat Exchangers

The short answer is that leaving your thermostat at a very low set point will almost always result in lower energy consumption. The long answer follows.
For most residential heating systems, the thermostat controls the heating system to maintain the set point (the temperature you set). It does this by turning the heating system on and off. As you would expect, the room temperature will fluctuate from the set point, unless you allow the heating system to cycle on and off very quickly, which will prematurely age your equipment.
During cold weather, your house is continually losing heat to the outdoors. It does this in several ways. Heat is lost by conduction through the surfaces of the house; warm air exits the house while cold air enters (infiltration); and to a lesser extent, your house radiates heat outward. Of course, it gets more complicated, since your house has a great many parts, each of which have different thermal conductivities, thermal capacities, and radiative properties.
The net effect of all this complicated heat transfer is that a typical house will (almost always) lose more heat when the inside temperature becomes higher relative to outside. I say “almost always” because it’s possible to have net heat gain on a cold day if it’s very sunny, and your house is well-insulated and sealed.

Barbeque (Charcoal Vs Gas) (Part I)

Charcoal barbeques are a must for that smoky flavour, but gas barbeques offer ultimate convenience. It’s no wonder a trend is emerging for people to have both.


Charcoal grill
The biggest pro for the charcoal barbeque is that classic, smoky flavour it gives to meat.
“A charcoal barbeque is a real meat-lover’s barbeque and connoisseurs enjoy creating different flavours using meat smokers and smoking pellets,” says Matthew Lawton of Mitre 10, who believes American brand Weber is behind some of the best charcoal barbeques you can buy.

Charcoal barbeques are inexpensive – a high-end unit costs around $400 and a very basic unit, $59. A good mid-range unit will cost $200. If you spend a little more you will enjoy the additional features and size benefits. However, charcoal barbeques have some factors that some may consider downsides. For instance, a charcoal barbeque can take up to 30 minutes to reach cooking temperature. They can also be a little on the messy side – with ashes to get rid of and bags of coal to buy. For many that’s all part of the job and the satisfaction of ‘caveman cooking’.

When choosing a charcoal barbeque check that it is easy to light, clean and remove charcoal. Because you’re ‘playing with fire’ Roydon warns that charcoal barbeques need to be watched carefully as they can get away on you and burn food.

Features your charcoal grill should have:

• Sturdy steel construction with a durable porcelain- enamel finish.
• Heavy-gauge charcoal grate.
• Large, easy-to-remove ash pan.
• Adjustable-height chrome-plated aluminium cooking grate.
• A locking lid for safety when transporting. 


Upgrade features: 

Shelves and warming racks, smoking ability, workspace, storage space, larger cooking grids, rustproof ash- catchers and porcelain-enamelled cooking grates. High- end grates are usually made of cast iron, porcelain-coated aluminium or even stainless steel.


Gas barbecues


Cooking doesn’t get much quicker than a gas grill, simply turn it on and it’s ready. These are ideal for people who have big families to feed or frequently entertain and want things to be quick and easy. The fact that gas barbeques are easy to clean is an additional bonus. Basic models will have a flat plate and a grill, but those wanting quality and style should seek out a stainless steel beast with a hood.

“If you fancy yourself an outdoor chef, a top-of-the-line gas barbeque such as the Gasmate Galaxy Quantum Pro or Stratos 4-Burner Gas Grill can literally become an outdoor kitchen. Look for features such as side-burners, rear burners, roasting dish, rotisserie and warming racks,” says Roydon.

“Gas barbeques start at around $600-$700 and can cost as much as $15,000,” explains Matthew Lawton, who says the top model stocked at Mitre 10 is around $5,000, but $1,500 will get you a great gas barbecue.

Features your gas grill should have:

• Sturdy steel construction with a baked-on porcelain- enamel finish.
• Heavy-gauge nickel or chrome-plated aluminium cooking grate.
• Twoseparateburners,withtwoseparatecontrolknobs for greater heat control.

Look for a durable barbeque that has sturdy construction, metal work and corrosion-resistant paint and fittings. Mitre 10’s Matthew Lawton recommends checking the grade of stainless steel.

“Look for 304 grade stainless steel which is durable – especially if your barbeque will be near the beach, as sea air causes rust.”

Upgrade features:

Shelves and warming racks, flip-up workspace, enclosed storage space, large cooking areas with up to six burners, improved cooking grates (as above), side burners for cooking sauces, rotisseries and infrared cooking abilities, smoker boxes or drawers and stainless steel construction.

The barbeque is to summer as sand is to beaches. Whether you’re looking for portable model for camping or a stainless steel, state-of-the-art appliance, Mitre 10 offers a range of barbeques to meet your needs.

About Plants and shade

Six Ways to grow in the shade
by Sandy Johnson

Shady areas can be difficult to get plants to grow in. The “trial and error” method can really test your patience and your gardening budget. There are a few simple tricks we can share with you to make gardening in the shade a success.

1. Shade level
Determine the degree of shade you are dealing with, as this will guide you to make better plant choices:
Full shade – This is an area that receives no direct sunlight. The shade can be cast from trees, fences or the walls of your house or your neighbour’s house.
Dappled shade – This is where there is a mix of sun and shade. The area will receive sun at some parts of the day directly or filtered through foliage.
Part shade – This is the easiest type of shade to deal with, as the area will only receive shade for part of the day and be in the sun for the rest of the day.

2. Treat the soil
In shaded areas, just as in the rest of the garden, it is important to treat your soil. It is not unsual to have dry, poor soil in shady spots, which will restrict growth. Before planting, add a liberal application of compost and dig it through the top layer of soil. Shady areas also need water, though not as much as areas in the sun, so water occasionally in the hottest times of the year.

3. Increasing the light
The more light that the area receives, the better the plants will grow. Thin out the branches from trees that are casting the shade or remove low branches. This will also give you more space to work in.

4. Root competition
This is a common problem in shady gardens as large trees responsible for shading have large roots that take up a lot of space. Their root systems also use the water and nutrients, making it very difficult for other plants to thrive. This is where plants with a small root system such as ferns and bromeliads are perfect.

5. Height
Add some height by using pots or containers. They can be planted with a permanent plant or changed every season with annuals. Using pots is also an effective way to get colour into a spot that might be very wet. A sculpture is another way of adding colour and interest to a dreary area.

6. Stick with a good thing
If it works, then plant more. If your plant choices are limited or the area is very large, then plant in large groups – this is an effective way to create a stunning display, especially when the plants flower. Choosing plants that flower in lighter colours like white, light blue and pink will also help to brighten shade.