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11 Solar Hydronics Design Considerations

02 Mar
11 Solar Hydronics Design Considerations

Home Design

Home design considerations include your level of passive heating, shading from trees or pergolas, your insulation, solar power, your comfort, energy recovery ventilation and energy loss through open windows, floors, ceilings, walls, windows, vents and cracks.

Your Year-Round Climate

The year-round weather at your home’s location is the first design consideration. You can check this by going to the Bureau of Meteorology website for your area. As an example, the year-round weather data taken from Burnley, an inner suburb of Melbourne, shows a temperate year-round climate of 19.9°C mean average and 8.9°C mean minimum. However, regional locations are typically colder in winter and often hotter in summer than a capital city such as Melbourne. For example, Ballarat in regional Victoria shows 17.4°C and 7.1°C respectively with winter minimums between 3.2°C and 4°C so additional steps to reduce energy loss are more important considerations than for a more temperate year-round climate:

Control Considerations

Zoning your heating and cooling system is one of the best ways to improve your household energy efficiency by heating rooms when they are used. Separating your living/family rooms into a separate zone from your bedrooms is the first step in zone control because these rooms are used at different times. Adding zones to other rooms that are used at different times or just occasionally will further help your household energy efficiency.

If you have installed solar panels but don’t have battery power storage, you should consider controlling your appliances to run during the day when the sun is shining. For example, consider running your dish washer, washing machine and dryer in the morning, then your heat pump water heater in the middle of the day (it will typically need about 3 hours of run time for 24 hours of hot water), then your heating or cooling system in the afternoon and turn it off at night. Your home is insulated to reduce energy (heating or cooling) loss and has thermal mass that will slowly release the absorbed heating or cooling energy into the evening. By drawing as little power as possible from the grid in the evening when the sun is not shining, you can further reduce your power costs.

If you have energy recovery ventilation, your home’s ability to retain the heating and cooling into the evening is enhanced. A pair of ERV units such as the Stiebel Eltron LT-50 can capture up to 90% of the outgoing heating or cooling energy in their ceramic filters. The price for a pair of Stiebel Eltron LT-50 energy recovery ventilation units sufficient to ventilate a standard sized living/family room is $2,400 (excl GST):

ERV units are designed to operate 24/7 using less than 1kW for a pair over a 24-hour period. They draw the air in using very small fans similar to those in your computer for just over minute absorbing the energy and storing it in their ceramic filters, then they expel the stale air out for about the same time delivering another load of energy to the ceramic filters. ERV units will help keep your indoor climate just right whilst also making it feel fresh and airy.


Combining Underfloor Heating and Radiators

Combining underfloor heating in your living and family rooms with conventional radiators in your bedrooms will reduce installation costs whilst still giving you a total solution of radiant heat. You can compare the difference of a total underfloor option with a half hydronic underfloor, half radiator system for your living/family rooms and half radiator option for your bedrooms using the Siddons indicative quote configurator:

For an underfloor/radiator option, you will require a water mixer to provide flow water to your radiators at around 60-65 degrees C and to your underfloor heating circuits at around 35-40 degrees C. A good hydronic heat pump can make water to 65 degrees C such as the Stiebel Eltron WPL17ACS or WPL25ACS:

Combining Radiant Heating and Reverse Cycle Air Conditioning

Combining underfloor or radiator heating in your living and family rooms with reverse cycle air conditioning will reduce your installation costs further. Radiant heating is the best form of heating and certainly best for people with asthma, so investing in this makes good sense for your living and family rooms, where you spend most of your indoor waking time. If you use your reverse cycle air conditioner to warm your bedrooms at night prior to going to sleep, you may not need to operate them through the night or only minimally such that the issue of blowing heat does not present itself. You can compare the difference of a total radiant heating option (underfloor and/or radiators) with a half hydronic radiant heating option for your living/family rooms and half air-conditioning option for your bedrooms using the Siddons indicative quote configurator:


Heating Bathrooms

If you choose underfloor hydronic heating, then Siddons Solar Hydronics recommends you install hydronic towel rails combined with the underfloor heating. This will provide extra heat in winter for these small rooms as well as keeping your towels dry:

Underfloor Hydronic Heating and Floor Coverings

Underfloor hydronic heating radiates through the floor at a gentle 26°C and therefore works well with almost any floor covering except softwood and bamboo floor boards. Underfloor heating works best with hard surfaces like tiles, plastics and engineered hardwood boards but will also works with loose weave carpets with resistance of less than 0.15 m2K/W. If you choose floor boards, the moisture content should be less than 10% at the time of installation to avoid shrinkage and no more than 25mm in thickness. Narrow boards with more joins are better than wider boards as they will provide more scope to absorb the natural expansion and contraction from heating and cooling cycles.

Slab or Suspended Timber Floor Considerations

Your design should consider site conditions such as sloping or flat block, which may affect your decision on whether to have a slab or suspended floor on footings and stumps. If you choose to use a slab, the soil type and drainage will affect heat loss from the underside of the slab. Research into slab heat loss has found that up to 50% of your home’s winter heat load can be attributed to heat loss through the ground, so this is a most significant design consideration. An insulated slab or insulated panels with screed over the top would certainly reduce this heat loss:

If you choose an insulated screed, the screed should be at least 65 mm in depth and allowed to dry for 4 to 6 weeks before the heating is applied. Siddons Solar Hydronics suggests that you set the flow water to around 25°C initially then increase the temperature by two degrees each day until you reach the set temperature of around 35°C. This will gradually dry out any residual moisture still in the screed and avoid cracks.

Alternately, you may choose a suspended floor on footings and stumps, particularly if you have a sloping block or poorly drained soil. If so, you should insulate your suspended floor to reduce heat loss to the underside. You can use insulation panels such as Tyco XPS foam panels which will also provide a base for your underfloor hydronic circuits.

Hydronic Pipes

Siddons Solar Hydronics recommends multilayer pipe such as Alupex for your hydronic circuits. Alupex is made from PEX with an aluminium sheath which resists oxygen entering the closed loop hydronic water and is both flexible and holds its form making it easier for installation. The oxygen in your hydronic water will deplete which is good for your hydronic system so keeping out new oxygen from entering through the PEX pipe wall will give longer life for your radiators by reducing the incidence of rusting, scaling and development of mould. PEX is crosslinked polyethylene and is flexible, resistant to scale and doesn't corrode or develop pinholes. Link to Alupex/shop

Siddons Solar Hydronics recommends the width between hydronic pipe circuits to be 200mm and 150mm in bathrooms and toilets due to the small floor area relative to the air volume. Hydronic pipes should be placed at least 100mm from, and not run underneath, walls, kitchen benches, cupboards and wardrobes. The maximum length of a hydronic pipe circuit should not be greater than 110m.


Magnetic Filter

If you have steel radiators, you should install a magnetic filter such as the Fernox TF1 to be constantly attracting small metal particles that will flake off your radiators over time. This filter should be check periodically. Siddons Solar Hydronics suggests you check it after the first year of operation to determine how often you should check it going forward.


Isolating Ball Valves for your Hydronic System

Siddons Solar Hydronics recommends the installation of isolating ball valves for your hydronic system on the flow and return lines to/from the buffer tank and to/from the heat pump. This will make servicing much easier in the future by being able to easily shut off the hydronic water:


Get in touch

There are many solar hydronic heating and cooling source methods available including air and ground source heat pumps, solar plates, and evacuated tubes.

To get an indication of what might work for you and the price, jump onto our online configurator, enter your information in response to the questions asked and receive an indicative quote.
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