Water Heating

Solar hot water: is more efficient than heating water electrically. A large well insulated hot water storage tank is also one of the best storage batteries for heat/cold. This could be coupled with a thermal Sand Battery for longer heat storage/transfer.

https://www.builditsolar.com/

Hot Water Uses

• Showers or baths
• Hands, face or body washing
• Dishwashing
• Washing machine
• House heating: hydronic underfloor heating pipes or radiators
• Pool/Spa water heating
• Sauna/Steam room

How much Hot Water?

• ~ 900L/d: 800L for 8 people/d, + 95L
• > 320L heating circulated hot water.

Showers/Baths: 800L

Just a 10 minute shower per person at a flow of 8L/m uses 80 litres/person. A full bath uses up to 80 litres of mostly warm/hot water also. This accounts for over 60% of household hot water use. Assume 75% of the water mix is hot so 80L/person of water is proportioned to 60L/person of hot water.

• 4 people need : 240L or more
• 8 people need: 480L
• 12 people need: 720L
• 14 people need: 840L
• Volumes doubled with longer showers.

Additional hot/warm water is needed: 95L

• Drinking: uses 7L ~ given 16L for 8 people assuming 2L/day/person cold water. 7L for 8 teas/coffees  where the use of pre heated water to reduce energy usage or an on-demand water heating tap.
• Handwashing: uses 32L ~ given 64L for 8 people 4 times daily. Assuming 2L per 20 second soapy handwash scrubbing leaving the tap running with warm water.
• Dishwashing: uses 30L~ given 9.5L of water per wash, while hand washing generally uses up to 60L. Pre heated water may assist reducing energy use. Approximately 30L hot water use combined for dishwasher and hand washing pots and pans.
• Washing Machine: uses 24L/d pro rata 2 washes/wk ~ given an 8kg WM with energy rating: 4.5 Stars (MEPS) Water Rating: 4 stars (WELS) Litres per wash = 81L.
• Toilet Bidet: uses 2L /d 8 people. A bidet tap may use only 1L per use with 25% warm water.

House Heating: 320L circulation, non potable water.

160L for 16 radiators for 6 bedrooms, 4 bathrooms and kitchen/dining/living /hall/entry/spare rooms. Given a radiator holds about 8 – 10 litres of hot water in them plus water pipes. Alternatively underfloor heating may be used, consuming less in pipework but requiring faster hot water flow to dissipate heat over floor space.

Heated water hydronic heating of radiators or underfloor piping, may use solar heating hot water, augmented by fireplace water heating, geothermal heat pump and/or electric/gas water heating boosters. Reduced heating energy is achieved with good insulation and thermal mass heat storage from solar radiation.

How Hot?

Shower water temperature should be between 37 to 42°c. A maximum temperature of 50°c at the outlets of each shower head or tap is required. As this is hot enough for a bath or shower, but not hot enough to cause severe scalding.

The joint Australian/ New Zealand Standard, AS/NZS 3500 – requires newly installed hot water systems delivering water to any outlet primarily used for personal hygiene purposes, such as basins, baths and showers, must be set at a temperature no greater than 50ºC in domestic settings and 45°C in child care, schools, aged care and hospital settings.

Solar Hot Water

Hot Water Storage

Safety considerations ensuring the installation of a hot water pressure release valve must be included, to avoid the possibility of hot water/steam pressure tank explosion during times of high heat.

Augmenting your primary hot water, as additional warm/hot water storage capacity.

Used Hot Water Storage tanks

>200L with ‘indirect heating inlets’, ensuring the tank is sound and has water pressure safety valves.

• Expensive new
• Low and mid capacity so may need multiple tanks. Large versions are found holding a maximum of 300 – 400L.
  • connected in series to your primary tank
  • Sometimes found discarded / cheap, as electric heating elements are not working, or people upgrading to/from gas/electric ones.

IBC Tote

An IBC tote dimensions 1200 x 1000 x 1160mm (L x W x H) & it weighs only 59Kgs empty.

When filled with water it weighs over 1 ton, plus the weight of any framework and insulation so would require a forklift or mini crane/pulley to move around later. Or emptied before attempting to move.

• Cost effective (AU$180) food grade,
• High capacity 1000L
• UV rays will cause plastics to degrade, harden and crack over time. Covers are available.
• UV resistant black HDPE – High Density Polyethylene (to avoid algae growth from sunlight)
• HDPE has a max working temperature 100°c, but hot water should be kept under 60°c.
• It cannot be connected directly to mains water pressure as it’s not a pressurised tank.
• Hot water in HDPE may not be suitable for ‘drinking’ given possibility of dioxins or a ‘plasticky’ taste or odour in the hot water possibly present, if water is left uncycled for over 6 months.

It is preferably:

• indirectly supplying heat to your hot water storage tank system, for bathing etc.
• a hot water battery storage, or for non drinking purposes like dishwashing or washing machines.
• Or directly (through a pressure pump).

A separate pressure pump system would need to be developed inbetween the tote and hot water supply. 12v hot water pumps offering adequate mains style pressure could be developed for off-grid situations. 

Best used  hot water battery storage for ‘indirect’ water heating such as for house hydronic heating radiators/underfloor, pool, kiln or drying/dehydration unit, or the primary hot water storage tanks system.

Heat can be exchanged indirectly by either;

• allowing the IBC tank hot water flow into another tank’s indirect heating coil inlet and returned, or
• Flow around a heating circuit like hydronic radiators/underfloor heating or radiator fans to dissipate heat for house warming.
• Flow to/from a ground source heat exchange unit to warm its refrigerant. 
• Pex piping coiled within the IBC tank can then be piped in/out to exchange heat and carry it to where it may be needed.

HDPE Plastic Drums

Cost effective (AU$40) 200L heavy duty used Food Grade HDPE plastic drums with clamped on lids. Similar characteristic to IBC tote except lesser capacity.

Thermal Storage Tubes

Attractive Perspex tubes, for direct sunlight heating thermal mass.

http://www.solar-components.com/TUBES.HTM

Movable Hot Water Battery on a pallet:

Water is an optimal energy battery storage system. This concept enables tank mobility to an optimal sunlit, warm or insulated position, or to be moved around during a house build as a single unit, whilst the right warm location is found for it to be integrated into the house structure later, or for a tiny home or permanent caravan placement, pool or other remote/off-grid hot water location. 

Use cases:

• Direct water heating and storage, using plastic tanks for generally non drinking heated water.
• Indirect water heating to hot water storage tank(s) that hold potable water.
  • Higher capacity hot water system for showers/baths, kitchen and bathroom tap water, washing machines, dishwashers, boiling water taps.

Tanks:

• A large hot water tank is ideal, with multiple tanks < 300L may be required to achieve upto 800L + storage. For potable and direct water heating and storage. Connected in series or such that the inlet of the primary tank is supplied by the hot outlet of the secondary tank and so on. Each tank can be indirectly heated from the separate warm/hot water circulation of a solar hot water collector or from a hot water battery.
• IBC Tote  offers 1000L 
• 200L drums/tanks; offers 200L, similar characteristics to an IBC tote, but less capacity and much cheaper.

Concept:

Encase a tank(s) like a hot water storage tank or IBC tote in thermal insulation, on a pallet, with glazing to capture sunlight radiation and warm the water and thermal mass within. Using an insulated thermal mass solid base and optionally walls, to additionally capture and store heat then release it slowly overnight, warming the tank. Warm water can be either used direct or indirectly heat another hot water heating system.

1. Lay out a waterproof membrane and rigid base board on a pallet. E.g. cement fibre board or heavy duty plastic base.
2. Build a frame with metal reinforcement mesh. Then layer a <20cm thick base of hempcrete atop as ground base level insulation and allow to dry a few days.
3. Place thermal mass concrete pavers on top of hempcrete to cover the footprint of the IBC tote. A thin layer of additional insulation like Polystyrene panels under the layer of pavers would improve insulation further. Alternatively sand may be used as thermal mass sand battery.
4. Test placement of the IBC Tote to neatly fit on the concrete base and affix just the front base.  So it may be removed easily for this build, repair or replacement.
5. Setting Forms up:
   • (using wooden boards), make a frame and form around the IBC tote. You can use the pallet base to assist erecting framing.
   • Walls should be 30cm thick
   • A walled form could be constructed prior to placing in the IBC tote, allowing for removal of the tank should repairs ever be needed or at the end of life of the plastic.
   • Double glazing fixed window frames could be added to side walls. Whereas the roof and front will need access doors/panels with glazing constructed, to  allow in sun light. As the top of the IBC tote and front requires access to tank cap and plumbing points.
   • Connect in plumbing pipes to connect tank connection to external piping. Ensure pipes are lagged with insulation. 
6. Pour in Hempcrete mix into your form to create 3 walls that encase the IBC tote. Allow to dry a few days.
7. With the IBC Tote in place and plumbing connected, matt black metal plates may need to be placed in front to encase it, then filled with sand around the IBC tote.
8. Build access panels with glazing for front and roof.
9. Lightly lime render the external hempcrete walls.  Ideally in matt black.
10. Ideally lime wash the inside and outside in matt black to absorb heat.
11. Place in a sunlit, unshaded position, like rooftop, with its front and roof glazing facing North, assuming you are in the Southern Hemisphere.

Materials:

• IBC Tote:  black/blue UV resistant, high-density polyethylene, protected & encased in a strong galvanised steel tube cage.
• Large pallet ideally 1.5m x 1.5m, to fit IBC tote with 30cm thick walls and allow space for plumbing at front and top.
• Base board: for pallet floor, like cement board or hard plastic, waterproof membrane.
• Metal grate reinforcement for base.
• Cement slabs, pavers or pour your own, or sand. As thermal mass.
• Hempcrete & lime render, lime wash ideally matt black.
• Wood framing
• Metal panels for front.
• Access doors
• Glazing, ideally double glazing or polycarbonate or glass.
• Thin polystyrene panels ~1.1 sqm
• Plumbing and pipes for an IBC tote.