STORAGE TANK CONSTRUCTION
The storage tank body and heat exchanger is fabricated from 2.2 mm (2.7 mm for HET models) hot-rolled, low-carbon steel sheet. The cylinder dome ends are pressed from 2.5 mm pickled and oiled steel sheet. The steel connection fittings are designed such that after enamelling, the vessel is free of bare steel surfaces.
During manufacture the steel connection fittings are robot welded to the domes, the cylinder body is rolled and welded, and the completed domes welded to the cylinder body to form a vessel. After welding the vessel is subjected to two pressure tests to ensure weld integrity and strength. The vessel is firstly sealed and submitted to an underwater test where air is applied at 100 kPa (15 psi). This ensures that seams are free of leaks. The vessel is then filled with water and hydraulically pressurised to 2,100 kPa (300 psi) for one minute (2 minutes on JIS vessels) to ensure the structural integrity of the welded seams. Finally, the storage tank is rapidly dried and placed into a shot blaster for final metal cleaning pre-treatment before being glazed.
An important aspect of this method of manufacture is that the storage tank and fittings are all completely welded prior to glazing. There is no welding carried out after the glazing is completed. This differs from methods adopted by other glass-lined vessel manufacturers. All steel used in the vessel is of a very "low carbon" content designed specifically for glass lining applications.
The internal surface of the vessel is lined with two coats of vitreous enamel (also known as glass lining). The glass lining is applied to protect the steel surface of the vessel against corrosion attack. Glass lining is considered to be the best method of corrosion protection available for steel vessels. Solahart adopted the glass lining process for a number of reasons including:
These characteristics are dependent upon the care in application of the enamel and the quality and formula of the materials used. Solahart adopted a manufacturing technique which provides a high quality, high-temperature resistant enamel. Once fired the enamel surfaces fuse with the steel base material and will not separate under standard operation conditions.
The enamel comprises a mixture of silicas and clays selected so that when they are fused, the resultant enamel has a coefficient of expansion comparable to that of steel. The vessel and clay mixture is heated to 860°C, the resultant enamel melts and fuses to the steel surface. On cooling the steel vessel contracts at a slightly greater rate than the enamel. The enamel is therefore under a slight compressive stress at low temperature. (Glass is extremely strong in compressive strength).
The resultant composite container is in effect an enamel vessel with a steel outside shell bonded to it. The bond between the glass and the steel has a far greater shear strength than the compressive stress given to it on cooling. In normal operation the vessel can be heated up to 99°C and will therefore tend to relieve only some of the pre-stressed compression.
In practice large and sudden temperature variations between the enamel lining and the vessel wall do not occur. Water has considerable thermal inertia, (time required for a temperature change with application or withdrawal of heat). The intimate bond of the enamel with the vessel prevents temperature gradients between the glass lining and the steel body.
The Solahart Primaglaze â process incorporates two enamel formulations:
A total enamel thickness of approximately 0.3 mm results from the two bonded coats.
The X class ground coat is applied directly onto the clean, shot-blasted metal surface, then dried and fused. The Y class cover coat is applied directly onto the baked ground coat, dried and fused to the ground coat. The interface with the ground coat becomes a continuous, diffuse zone of intimate bonding of full enamel ranging from steel through ground coat to cover coat to form one composite protective wall 0.3 mm thick.
This two-coat Primaglaze â system was pioneered by Solahart and is essential for the long life under the high temperature conditions encountered by solar hot water systems. It allows for the use of large collector areas and higher performing collectors improved winter performance is possible without concerns for high temperatures during the summer months affecting the vessel enamel lining
The same relationship of collector area to vessel volume could be damaging to systems constructed of copper or stainless steel. In particular, excessive summer temperatures may cause premature vessel material failure.
Solahart vessels are fitted with a replaceable magnesium anode (alternate aluminium alloy anodes are also available for exceedingly hard waters). The use of an anode in corrosion protection is known as a cathodic protection system.
The anode is used to protect any "holiday" or minute areas not covered by the enamel lining. The anode will sacrifice itself and plate any bare metal areas exposed to, and in electrical contact with, the anode. To maximise anode life, the area of bare metal surface exposed to and electrically connected to the anode must be minimised. The Solahart design ensures this through a combination of enamelling processes and vessel design.
Design features to achieve this result include:
These features ensure the longest life possible from the specially selected anode used in the Solahart solar tanks.
In the Solahart vessel, the anode has very little "work" to do, consequently its life is dependent on other factors such as:
Essentially the life of the anode is determined by its natural solubility in the water in which it is immersed. For this reason, the life of the anode is quite variable. For example, tests show that with average quality water supply, the life of the anode is greater than ten years. However, with these average quality water supplies, a few anodes may last as little as five years, whilst others last more than fifteen years.
Due to this variation in actual life, we strongly recommend that as a matter of caution all anodes are replaced after five years. Remember, the anode is inexpensive and is simple to replace. Replacing the anode is much less expensive than replacing the vessel. The ability to easily change the anode is a major design advantage which Solahart holds.
Most water authorities in Australia require that the Pressure and Temperature (P&T) Relief Valve be replaced at intervals not exceeding 5 years and that the vessel and collectors (L Series only) be drained and flushed free of sludge and other deposits. Anode changes carried out during these mandatory services become very inexpensive.
In areas with poor quality water supplies the anode may need to be changed more frequently than five years. Your local Solahart dealer will be aware of the water quality in your area. The recommended anode change period is listed in the Owner's Manual supplied with Your Solahart.
Aluminium anodes are also available for poor water areas. Aluminium anodes should only be used where the TDS is greater than 1,000 ppm.
Anodes deteriorate under two inter-related mechanisms.
Tests reveal that the self dissolution rate markedly increases with the rate of cathodic protection. By virtue of the two coats Primaglaze â enamel design the Solahart anode has less cathodic protection demand than comparable glass lined hot water containers. As a result enjoys a longer service life.
All hot water vessels rely on a "lining" to protect them from corrosion. Both stainless steel and copper tanks rely on protective oxide films, which are capable of breakdown in natural water supplies. Stainless steel is not totally stainless and is susceptible to various insidious forms of corrosion such as stress and crevice corrosion. This is particularly prevalent when, in the presence of high temperatures, the metal is subject to high operational stress and high chlorides.
Corrosion is a chemical reaction that takes place on the surface of a metal. By far the most common reaction, that seen in the rusting of iron, is the reaction with water and dissolved oxygen.
The severity of the corrosion attack from fresh water on metal varies widely, depending on the dissolved salts and gases contained within the water. The principal agents for corrosion are chlorides, sulphur compounds, iron compounds and calcium salts.
Corrosion occurs by a number of mechanisms, however in the case of water heater cylinders they are mainly :
To better understand these mechanisms it is necessary to explore them closely so that the best forms of defence can be developed. Once the mechanisms are clearly understood it then becomes a relatively simple matter of direct side by side comparison to form an educated opinion of the best materials for the application.
(ii) Within the primary pit positive metal ions (Fe+2) dissolve and accumulate. These attract chloride ions (Cl-) which are present in the water supply.
(iii) The metal chloride (Fe+2Cl-) concentration begins to build up in the pit but this hydrolyses to give hydrochloric acid : Fe+2 Cl2- + 2H20 = Fe(OH)2 + 2H+Cl-
(iv) The combination of chloride ions (Cl-) and hydrogen ions (H+) then accelerates the attack.
(v) Crevice corrosion follows the same path as pit corrosion since the crevice serves as a ready made pit in which the oxygen concentration is low.
For example many stainless steels that rely on passive surfaces for corrosion protection exhibit pitting attack because of the large potential (voltage) difference between the passive and active regions of the pit, chloride ions are known to destroy passive layers.
(ii) A corrosion pit forms by the mechanism of pit corrosion described above.
(iii) The pit forms a crack initiation point and the cracks propagates as stress corrosion cracking.
(iv) Mechanical rupture, not involving corrosion, occurs.
Most metals tend to fracture under repeated cyclic stress similar to that experienced within a hot water system when the water is drawn. This fracturing process provides the entry point for pit corrosion to develop as described above. The corrosion process reduces the effective metal thickness, reducing the ability of the device to withstand the cyclic stresses to which it is subjected. Ultimately the metal will fail.
Potential (voltage) difference develops between two dissimilar metals when they are immersed in conductive water supplies. This potential difference produces an electron flow between the two decreasing the corrosion rate of the more resistant material and increasing the corrosion rate of the less corrosive resistant material. Welding processes used in the construction of some stainless steel water heaters create the potential for the introduction of galvanic corrosion by altering the metal properties around the weld area. In well-designed Vitreous Enamel lined water heaters the weld area is completely covered after welding, effectively removing the threat of Galvanic Corrosion reactions.
The water stratifier prevents mixing of the cold water entering the vessel with the hot water already contained therein. This promotes thermal stratification of the vessel contents.
The stratifier achieves this through a combination of its conical shape and inverted outlet slot. The velocity of the incoming water is dropped and inertia dissipated by the stratifier. the cold inlet water drops from the stratifier through the inverted outlet slot and lies on the bottom of the vessel. The temperature of the hot water already in the tank is therefore not diluted and as a result, the hot water delivery capacity of the system is enhanced.
The stratifier is moulded from polypropylene (PPK 2032) which is inert, non toxic and approved for use in hot water systems.
The water stratifier:
The vessel is fully encased in pressure injected polyurethane foam. Polyurethane has a very low thermal conductivity, (about half that of fibreglass - 40 mm of polyurethane has similar insulation properties to about 70 mm of fibreglass). Solahart vessels have an average 60 mm of polyurethane around the hot section (the top two-thirds of the vessel). The vessel is located low in the insulation casing so that in summer, if the total vessel contents reach 90°C, excess heat is dissipated through the bottom one-third of the vessel. This prevents over-heating of the system.
The asymmetric insulation profile is very deliberate and arranged in a way that is proportional to the normal, stratified temperature of the vessel contents. Heavier insulation over the upper sections of the vessel ensures that the hot water is kept hot for extended periods. Lighter insulation over the lower sections of the vessel allows a controlled level of heat rejection in those cases where the vessel is approaching an over-heated condition. The polyurethane insulation contains no chloro-flouro carbons (CFCs).
A fully foam-encapsulated vessel ensures that there is no direct heat flow path through the foam envelope. The insulation foam adheres to both the aluminium outer case and the surface of the vessel thereby forming a vapour-tight skin. The skin ensures the polyurethane foam retains its high insulating qualities that are not normally possible in free rise unsealed foams. Similar benefits are not offered by blanket or free-rise form insulation types.
Solar water heaters differ from conventional water heaters in two fundamental ways. The first and most obvious are that much of the primary energy used to heat the water is provided free by the environment in which the heater is placed. The second difference is that the input to this primary source of energy varies from season to season. Often annual variation ranges from low levels of solar energy at times of greatest need to excessive level at times of least need.
Not only does the primary energy source vary with the seasons, it often varies widely from day to day. If this free energy component is to be maximised under these circumstances the storage capacity and insulation properties of a solar water heater need to be greater than those of a conventional hot water system. This way it is possible to accumulate some residual energy from a previous good day to one for which the solar input may be insufficient.
Solar hot water systems also require auxiliary energy supplies. These are usually provided as thermostatically controlled electric or gas booster elements, (which may be manually or automatically initiated). Auxiliary elements provide energy on demand and act to "smooth out" the energy input fluctuations of the solar components.
To ensure that an auxiliary element does not waste energy in heating water beyond that required, the element is located in the centre of the vessel. This way the element heats only the top half of the stored water.
The external case of the storage tanks and heat exchangers are made from two sheets of aluminium that are lock seamed together. The top section is 0.4 mm thick with a stucco finish and the base has a brush finish and is 0.7 mm thick.
The polypropylene end covers ensure weather sealing to the case edges and the fittings. Concealed hand grips built into the end covers ensure ease of carrying. The case body and end covers derive considerable strength and rigidity from the high density polyurethane foam insulation that adheres to all internal surfaces including the plastic ends.
The material used for the end covers is polypropylene utilising the most effective combination of chemical stabilisers and finely ground carbon black. This gives excellent stability under prolonged exposure to ultra-violet rays, and high temperatures. In-field experience and in-house tests prove that the material is stable and inert. It will retain its toughness and flexibility without cracking in sunlight or at temperatures between -20°C to 104°C.
The steel connections in the vessel potable water compartment are protected against corrosion by the two coats of Primaglaze â enamel. The enamel inside the socket is applied up to, but just short of the thread. A polypropylene ferrule with a silicone O' ring attached is seated on the enamel surface to form a water-proof seal between the water in the tank and the brass fittings. As the brass plumbing fittings are screwed into the sockets, the feathered edge on the ferrule provides a seal to ensure a water-proof transition between the fitting and the tank socket. This ensures that bare steel is not exposed to water.
The thread size on the hot and cold water connections is 20 mm
PRESSURE & TEMPERATURE RELIEF VALVE
From a statutory compliance and safety perspective, this is the most important valve in the system. It must be fitted to all un-vented systems. Only systems that are permanently open vented do not require this valve.
The valve is located in the hot water outlet connection to the vessel through the tee adaptor. The valve probe extends through the tee adaptor and into the vessel. The tee adaptor branch is the hot water outlet connection and is available in either 15 mm (1/2" BSP) or 19 mm (3/4" BSP). This arrangement allows hot water to be drawn off over the P&T Relief Valve Probe. This is an additional safety precaution. In the event that calcium or other deposits built up on the probe, its operation may be impaired. In requiring hot water to be drawn past the probe, flow rates will fall if build up becomes extensive. This will generally alert the user to the need for service to the valve.
This valve assembly comprises:
The valve assembly is a mandatory requirement except in those circumstances where it can be guaranteed that the water supply pressure will not exceed 450 kPa (65 psi). If the combination valve is not used a check valve and 600 kPa (or less) cold water relief valve must be fitted.
The cold water relief valve is a sub-assembly of the combination valve. It acts as the primary safeguard against excessive vessel pressure. The Cold Water Relief Valve setting is 600 kPa (87 psi), 100 kPa lower than the P&T Relief Valve.
The cold water relief relieves pressure build up in the vessel arising from the expansion of water as it is heated. It is designed to operate in preference to the P & T Relief Valve.
Conventional hot water systems are generally not fitted with Cold Water Relief Valves and instead, rely on a P & T Relief Valve to relieve thermal expansion. In this case, hot water regularly passing across the valve seat will gradually build up substantial mineral deposits. This has the effect of either rendering the valve inoperable due to blockage or changing the valve seat causing it to continually discharge.
In the Solahart design, since the water relieved from the Cold Water Relief Valve is drawn from the bottom of the tank, it is relatively cool. This ensures deposits do not build up and seat damage is avoided. Further, the P & T Relief Valve can then be treated as a true safety device, only required to operate under emergency conditions.
Under normal circumstances, the Cold Water Relief Valve will relieve between 5 & 30 litres per day (depending on hot water usage, solar energy availability and booster operation.)
A Stop Tap is not included in the parts' boxes. A stop tap must be supplied by the installation plumber if one is not already installed in the cold supply pipe line for the heater. This tap is used to isolate the solar hot water system from the water supply for maintenance and service procedures.
In open circuit thermosiphon systems the potable water in the storage tank continually circulates through the collectors. This occurs when, solar radiation heats the water in the collectors to a temperature above that of the water stored in the tank. A natural circulation("thermosiphon") is induced by the associated density difference.
Open circuit thermosiphon system must only be installed in non-frost, good quality water areas. Water with a high solid's content can impair the efficiency of the collector over time due to calcification of the collector waterways. Under frost conditions, collector waterways can freeze and rupture.
A closed circuit J System with a heat exchanger must be installed under either of these conditions.
The L System comprises a double glazed vitreous enamel storage tank and fin-and-tube type collectors incorporating copper.
All the connections between the collectors and the tank of the L System utilise silicone O' ring type seals.
The cold water inlet connection to the storage tank is situated on the elbow of the collector cold water return pipe.
The L Collector comprises a copper tube water circuit bonded to an aluminium absorber plate and mounted within an aluminium case. The case has 55 mm polyester back insulation, 13 mm side insulation, low-iron, tempered glass and aluminium glazing trim. The absorber plate is treated with a black polyester powder coat finish.
L Collectors are for use with open circuit systems (where potable water passes through the collectors). Open circuit operating pressures of up to 1,400 kPa are acceptable. The collectors operate at 700 kPa (max) in the L System configuration.
The Solahart closed circuit system comprises a double glazed vitreous enamelled vessel surrounded by an outer steel jacket. The space created between the vessel wall and the jacket forms heat exchanger volume that is coupled to the J or K Collectors to form a closed circuit. During installation the closed circuit is filled with a heat transfer solution ("Hartgard") and water. This provides the medium for transferring the heat from the solar collectors to the vessel. The potable water stored in the J Tank and HE Heat Exchanger does not circulate through the collectors or jacket. Solar energy collected in the closed circuit is transferred to the potable water through the vessel wall.
A closed circuit solar hot water system provides a number of advantages over conventional open circuit systems:
The solar energy collected by the solar collectors is transferred to the water in the vessel across the steel wall of the vessel.
The large heat exchange wall area, combined with a low heat exchange rate, assures the glazed inside surfaces are not excessively heated. This minimises the build-up of scaling on the inside of the vessel.
Hartgard is the registered Solahart trade name given to a proprietary heat transfer solution. It is manufactured to comply with strict health and water authority regulations under food-grade conditions.
The Hartgard solution is supplied in 4.5 litre containers. During installation water is added to the closed circuit after the Hartgard solution has been introduced. The solution will protect the system against freeze damage down to -40°C. Corrosion inhibitors also added to the Hartgard solution will protect the system against internal corrosion damage.
The Hartgard solution is mixed and pre-packaged under food grade conditions to the following Solahart specifications:
Polypropylene glycol USP food grade 90% Freeze protection
Di potassium mono hydrogen phosphate 4.5% Corrosion inhibitor
Edicol blue colouring dye, food grade 0.008% Indicator
Distilled water 6% Mixing agent
Polypropylene glycol is used in the food, pharmaceutical and cosmetic industries, and for other applications involving possible ingestion or absorption through the skin.
Polypropylene glycol is permitted for use as a direct or indirect food additive by the Food Additive Regulation under the Federal Food, Drug and Cosmetic Act 1974, and by the meat inspection Division of the US Department of Agriculture.
When the polypropylene glycol is mixed with the water in the closed circuit of a two collector Solahart system the concentration is reduced to approximately 18 %. At this concentration the solution will remain fluid to approx. -10°C. Below this temperature ice crystals will form. At -15°C, free flow will cease. The mixture does not increase in volume over this range. Down to -40°C the mixture does remain sufficiently fluid when small force is applied. As a result collector freeze damage does not occur.
The long-term stability of Hartgard has been extensively tested by Solahart. Tests have shown that over a prolonged period at temperatures of 100°C, the Hartgard will not sludge or decompose, provided oxygen is excluded from the system. The sealed, closed circuit Solahart system ensures this air-tight requirement is met.
DI Potassium mono Hydrogen Phosphate is added to the Hartgard solution to import reserve alkalinity. This provides the corrosion inhibitor properties. As supplied, the Hartgard solution has a pH of 9.5 but this falls to between 8.5 and 9.0 in service. Initial oxidisation of the propylene glycol when water is added to the closed circuit is prevented by the di-potassium mono hydrogen phosphate.
The di potassium mono hydrogen phosphate is mixed with the propylene glycol as a white powder dissolved in 0.3 litre of distilled water.
Edicol blue colouring dye is added to the di-potassium mono hydrogen phosphate/propylene glycol/water mix to complete the Hartgard solution. It acts as an indicator to alert users if Hartgard has entered the potable water circuit. Due to the pressure differences between the closed circuit (80 kPa) and the potable water storage tank (600 kPa) it is extremely unlikely that Hartgard will ever enter the potable water circuit.
NOTE: Do not spill Hartgard onto roofs that are used for rain water collection. Any spillage will cause the rain water to develop an unusual taste. This will require complete replacement of the rain water tank contents. This important point must form part of all installation and service training programs.
This valve is fitted to the jacket vent connection, positioned at the highest point of the closed circuit. The valve is designed to relieve initial expansion of the heat transfer fluid during the first few heating cycles. The PR6 valve has a discharge capacity of 100 litres/hour at 80 kPa. The valve ensures that the jacket pressure under all operating conditions does not exceed 80 kPa.
The valve is designed to seal against the negative jacket pressures that occur when the solar collectors are cool. The closed circuit pressure can reduce to as low as -10 kPa. Under partial vacuum conditions, the collector and jacket are designed to flex without being damaged, to accommodate volume changes.
During the first four heating cycles, the PR6 valve will operate several times until the hottest operating temperature (highest jacket pressure) has been achieved. The volume of fluid expelled during the stabilising period is approx. 0.6 litres. The normal operating pressure range is -10 kPa to +80 kPa.
The fittings used to seal the closed circuit and connect the solar collectors to the jacket are based on Teflon-coated brass cones. The cone design takes account of the particular difficulty associated with containing low surface tension fluids such as propylene glycol. The design relies on a controlled deformation of the cones onto the copper pipes over which they are secured. The cone will also partially deform as it mates to the inside face of the jacket and collector sockets.
The cones and gland nuts are coated with food grade Teflon to enhance the sealing process and to allow for future disconnection of the fittings. The maximum operating temperature of the Teflon coating is 200°C. It's important that the Teflon coated parts are not exposed to temperatures above this. (As a result of welding or brazing for example)
NOTE: As the sealing takes place through deformation of the cones, the pipe assemblies should be fully replaced if a fitting has to be disconnected.
With this cold pipe arrangement, the temperature in the vessel is more uniform than for conventional "long" cold pipes. That is, the difference in temperature between the top half of the vessel and the lower half of the tank is less than with a long cold pipe. The total energy stored in the tank is equivalent although some advantage is gained since the water temperature varies less as water is being drawn off.
This collector can only be used for closed circuit applications. The absorber panel is pressed as two plates each incorporating half the integral header and riser waterways. The two halves are paired and placed face to face to form one absorber panel. The absorber plates are spot welded together using 1,440 spot welds at approximately 28 mm centres and then continuously seam welded along the headers and sides. Four steel collector sockets are then automatically welded in place at each header section end.
The completed absorber panel undergoes a structural integrity pressure test followed by a high intensity leak detection test. The absorber surface is chemically cleaned and finished with a polyester powder coating baked at 250°C.
The painted absorber panel is fitted into a folded aluminium case, over a 55 mm polyester insulation batt. The cool sides are insulated with 13 mm polyester strips. A drain channel is fitted between the case and the insulation batt along the top and bottom edge. This prevents the insulation absorbing moisture, even after long periods of wet weather. This feature ensures that the absorber panel remains dry and avoids the risk of external corrosion. The absorber panel is held in position by polypropylene corner blocks that accept the collector sockets. The blocks also act to increase the torque resistance of the sockets. The collector socket connections in the aluminium casing are weather-proofed with moulded EPDM seals.
The low-iron, tempered glass is fixed to the aluminium tray with a "closed cell" PVC pressure sensitive foam tape incorporating acrylic adhesive on both sides. A second PVC foam tape seal is applied to the top edge of the glass. An aluminium glazing trim is then fitted, and secured with blind pop rivets.
The K Collector is identical to the J Collector, except for the absorber panel finish. The absorber panel is first nickel plated on both sides, followed by a black chrome plating on the top face only. The selective black chrome surface finish increases the solar radiation absorbed and decreases the heat emitted from the absorber panel when compared with painted finishes. The difference in performance between selective and non-selective surface finishes may be up to 20% in low radiation or ambient temperature conditions.
The I Collector is designed for use in closed circuit thermosiphon or forced (pumped) circulation applications for which the exclusion of oxygen cannot be guaranteed. The absorber panel incorporates 25 mm diameter headers and seven rhombic shaped risers fused to an aluminium absorber plate. The absorber plate is treated with an anodised nickel selective surface. The large diameter headers of the I Collector ensure its suitability for large array configurations.
The Heat Dump Kit must be fitted to 302K, 303K and 443K systems installed on high solar radiation areas.
The Heat Dump Kit uses a temperature actuated valve that begins to open at 73°C on rising temperature and is fully closed at 65°C on falling temperature.
The Heat Dump Valve is fitted to the vessel tail end socket and the Heat Dump Pipe links the valve to the vessel cold water inlet connection.
Without some form of heat control, solar hot water systems using selective surface collectors can overheat during high solar radiation, low hot water use conditions. Typical vessel temperatures under these conditions can be as high as 95°C. At these temperatures, the P&T Relief Valve may otherwise operate.
When water at the position of the vessel tail end socket (centre of the tank) is between 65°C and 73°C, the Heat Dump Valve opens and allows hot water to circulate through the valve and Heat Dump Pipe. Heat is rejected from the Heat Dump Pipe and the temperature of the water falls by about 10°C along the length of the pipe. In this manner heat is only dissipated from the lower half of the container and the hot water outlet temperature of the vessel is not affected.
The Heat Dump Kit will usually come into operation on the third day following two days of full sun and no hot water load conditions.
The Heat Dump Pipe is designed to dissipate heat during stagnation conditions and therefore cannot be insulated. Tests show the pipe will not be damaged under freezing conditions down to -20°C over approximately 50 freeze thaw cycles.
During extreme freezing conditions the Heat Dump Pipe commences freezing midway along its length. Since both ends of the pipe do not freeze, ice formation is from the centre of the tube out toward each end, expansion pressure from water to ice is therefore relieved back into the warm container and no pipe damage results.