Tiny Homes

Tiny House Chronicles: A Plumbing Polemic

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Published on the Doomstead Diner on July15, 2016

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The ongoing tiny house chronicles: A venturi exhaust system for the shower stall and solar hot water arrays incorporating a direct HWC

Geoffrey Chia, July 2016

DIAGRAM 1  DIAGRAM 2  DIAGRAM 3  DIAGRAM 4 HeatpipeCoreEvacTubes

DIAGRAM 5 HollowCoreEvacTubes  DIAGRAM 6 HollowCoreEvacTubes  DIAGRAM 7 Thermosiphoning HeatpipeCoreEvacTubes  DIAGRAM 8 Thermosiphoning HollowCoreEvacTubes

VENTURI EXHAUST SYSTEM FOR THE SHOWER STALL:

I could not find any "off the shelf" exhaust fan models specifically designed to be located in a shower stall which operated on 12V or 24V DC.
A simple computer-type fan can certainly do the job, at least in the short term, and there are many of suitable size eg 12cm diameter, which can run on 24V DC diagram 1. However even if rated as "moisture resistant" they may not cope with sauna type humidity and are likely to fail prematurely. Even though they are quite cheap, the idea is to seek durable items and not be forced to keep replacing them. Furthermore heat loss from this open vent will be substantial, especially at night. A removable internal insulated cover can be added, however that will be another finicky add-on.

24V DC blower type ducted fans are easily available but are probably not suitable to be used "in-line" for air extraction. If embedded in the wall, due to the longer profile than a computer fan, it will stick out awkwardly. Even if mounted exteriorly and extracting air via a duct, it will be directly exposed to the sauna type moisture and may also fail prematurely, being made to do a job it was not designed to do. One way to ensure it has no contact with such moist air is to position the blower upstream of the shower exhaust port, to create a venturi effect to suck air out of the shower stall diagram 2. This will admittedly be an experimental system however I received no practical objections to the design from the intellectual resource folks I consulted (Doone W: scientist, engineer, geologist and homesteader, Lara N: architect, designer & builder, and Lara J: mathematics and physics expert). Any failure in execution of this system will of course be the fault of the author. This system will sacrifice some efficiency for better durability and longevity. If the external "inverted U" pipe or duct is well insulated, this configuration will help prevent heat loss because warm air from within the tiny house will tend to sit static in the top bend of the inverted U at night when the external atmosphere is cool (unless there are strong external breezes).
 

ADDITIONAL HOT WATER SYSTEM OPTIONS:

Roof mounted solar tube arrays utilising direct hot water cylinder (HWC) on loft floor

Designing a system in theory is one thing, but in practice we must always modify the design according to whatever components are available to us in the real world. I was offered false hope about obtaining a small indirect copper hot water cylinder by the false advertising of a UK vendor on eBay. Having now found the option of an affordable, small 50 litre simple direct HWC from an Australian vendor (diagram 3), this can be incorporated into the system and placed in the loft to increase the volume of hot water available and reduce concerns about inadequate pressure head for the taps. Unfortunately the roof mounted options require an additional small electric water pump and a small solar PV panel, however these are simple robust devices with good longevity. All these solar hot water system options remain free of dependence on microprocessors.

 

"Heat pipe core" type tubes (manifold on top of array) diagram 4

Caveats of this system: the manifold does NOT use glycol for heat exchange through internal copper coils in the HWC, water is circulated through a direct HWC. Hence it is NOT suitable for locations prone to substantial frost and subzero temperatures. However occasional ground frost should not be a problem as this should not affect the roof mounted system.

Pipes and Circulation:

All pipes are insulated except pipe 6, the overflow pipe from the header tank (which drains externally)

  1. Each morning, water is actively pumped from the rainwater tank at ground level into the header tank (this inlet pipe is not shown in the diagram for simplicity). Water from the header tank passively flows down through wide calibre (DN32) pipe 1, through the low resistance valve, filling the loft HWC to the brim and also filling pipe 5 up to the same level as the water level in the header tank.

  2. Water passively fills the electric pump which hence becomes primed. During the day when there is sunlight striking the PV panel, the pump drives water up pipe 2 and through the heated manifold into pipe 3. Note this manifold circuit will therefore automatically bleed air out by itself during initiation.

  3. Pipe 3 joins pipe 1 but cannot backfill into the header tank due to the presence of the upstream valve in pipe 1. Water in pipe 3 is hence forced into the HWC. Water circulates continuously through this HWC/manifold circuit in the day, progressively heating up the water in the HWC but this flow ceases at night when there is insufficient light to power the solar PV panel.

  4. Pipe 4 supplies the hot water taps. As water is extracted from this pipe it is replaced at the base of the HWC by cooler water from the header tank. At night there will be thermoseparation between the top hot layer of water and bottom cooler layer.

  5. If the sunlight is too intense and the pump is working too fast, causing the loft HWC to overfill and overflow via pipe 5 into the header tank, then the flow rate from the pump must be dialed back with the potentiometer. The expectation is that the potentiometer will be set for the brightest summer day and thereafter be fixed in that setting and not need attending. The loft HWC cannot overpressurise or boil over because such pressurised water will spill over from pipe 5 into the header tank and be replaced by cold water via pipe 1. Water in the header tank does not overheat due to the large volume of water here. as well as the heat being radiated out of the steel walls of this uninsulated matt black header tank.

  6. Over filling of the header tank in the morning is seen through the kitchen window as external spillage via pipe 6

 

"Hollow core" type tubes (small HWC on top of array) diagram 5

Pipes and Circulation:

All pipes are insulated except pipe 6, the overflow pipe from the header tank (which drains externally)

  1. Each morning, water is actively pumped from the rainwater tank at ground level into the header tank (this inlet pipe is not shown in the diagram for simplicity). Water from the header tank passively flows down through pipe 1, through the low resistance valve, filling the 50 litre loft HWC to the brim.

  2. Water passively fills the electric pump which hence becomes primed. During the day when there is sunlight striking the PV panel, the pump drives water up pipe 2 into the rooftop 30 litre HWC, filling it eventually to the outlet of pipe 3.

  3. Pipe 3 joins pipe 1 and although the pressure head in pipe 3 is higher than pipe 1, water cannot backfill into the header tank due to the presence of the valve in pipe 1. Water in pipe 3 is hence forced into the 50 litre loft HWC. Water circulates continuously through this loft/rooftop circuit in the day, progressively heating up the water in both HWCs but this flow ceases at night when there is insufficient light to power the solar PV panel.

  4. Pipe 4 supplies the hot water taps. As water is extracted from this pipe it is replaced at the base of the HWC by cooler water from the header tank via pipe 1. At night there will be thermoseparation in the loft HWC between the top hot layer of water and bottom cooler layer. There is no flow down pipe 3 at night.

  5. There is normally free movement of air to and fro within pipe 5. The HWCs cannot overpressurise or boil over, because overpressurised vapour will exit pipe 5 (and will ultimately vent to the external air via pipe 6). If the sunlight is too intense and the pump is working too fast in the day, causing the rooftop HWC to overfill and overflow via pipe 5 into the header tank, then the flow rate from the pump must be dialed back with the potentiometer. The expectation is that the potentiometer will be set for the brightest, longest summer day and thereafter be fixed in that setting and not need attending. This overflow scenario is very unlikely if pipe 2 is narrow in calibre, thus limiting the inflow rate into the rooftop HWC, and pipe 3 is wide in calibre thus enhancing the outflow rate.

  6. Over filling of the header tank in the morning is seen through the kitchen window as external spillage via pipe 6.

 

NOTES: in this system, the rooftop 30 litre HWC is treated as no different from a simple manifold. Hence the water in the rooftop HWC is "dead water" being generally unavailable for use*. Total available hot water remains 50 litres from the loft HWC only. The system will NOT work properly (for reasons too complicated to get into here) if water is pumped into the rooftop HWC at the level of pipe 3 connection and is drained from the base of the rooftop HWC at the level of pipe 2 connection.

 

*It will be possible however to manually harvest the hot water from the rooftop HWC at night from pipe 7 by opening the manual tap as indicated in the diagram. This tap in pipe 7 must be kept closed in the day for the system to function (otherwise water will merely circulate between pipe 2 and the loft HWC without going up through the solar array)

 

**Alternatively the connection in diagram 6 with an additional valve in pipe 4 should work well without the need for manual input. In this system, there will be an abrupt reduction of flow rate from a hot water tap when the rooftop HWC empties and the hot water then derives from the loft HWC. The disadvantage of this arrangement is that having a extra valve in pipe 4 can further reduce the forward flow rate from the loft HWC compared with diagram 5. To minimise this, it will be necessary for pipes 1 and 4 to be as wide as possible.

 

Thermosiphoning solar tube arrays utilising direct hot water cylinder (HWC) on loft floor

Whether or not the arrangements in diagrams 7 and 8 will work is unclear, because the basic direct HWC is not designed for thermosiphoning. Proper thermosiphoning cylinders have a convex top, in the centre of which is located the hot water outlet. Furthermore the connection ports are larger.

In diagram 8, air at the top of the 30 litre HWC may be an issue, however it should be possible to manually bleed most of this air out using the pressure release port at the top. I intend to give them a try.

 

Potential issue with all these systems: If the level of water in the header tank drops below the top level of the loft HWC, there will no longer be sufficient driving pressure to expel water from the latter. This can easily be resolved by refilling the header tank, a matter of turning on a switch.

 

G. Chia, July 2016

Ultimate Tiny House Design

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Published on the Doomstead Diner on March 16, 2016

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PENULTIMATE AND ULTIMATE PASSIVE SOLAR AND PLUMBING DESIGNS FOR THE TINY HOUSE

 

Figure0ventingfromHWCERRATUM:

Please note the last diagram in the addendum of this article http://www.doomsteaddiner.net/blog/2016/02/20/tiny-house-electrics/ was incorrect and the correct diagram should be this one:

 

INTRODUCTION:

The latest internal configurations shown here represent what I describe as the penultimate and ultimate passive solar and plumbing designs for a tiny house on wheels. If in the future I am able to tweak things to achieve additional improvements, I reserve the right to describe later revisions as the "super ultimate version" or "superduper ultimate version" etc, etc, outrageous ironic hubris intended.

In all versions I have always located the LPG stove and wood stove side by side (and the sink next to the LPG stove) so that a single rangehood can extract vapour from either stove, and to facilitate quick transfer of hot pots and pans from either stove to the nearby sink.

As mentioned in previous articles, passive solar heating requires broadside orientation of the dwelling to the sun, expansive double (or triple) glazed glass windows/doors on the sun-facing aspect, thick insulation of floor/walls/roof and a source of thermal mass. For a tiny house on wheels, concrete is not appropriate thermal mass, it is dead weight on the chassis. Water however has a high specific heat capacity and, weight for weight, offers superior thermal mass to concrete. Water tanks can be emptied when the tiny house is transported.

My initial intent was to locate internal water tanks(s) under the lounge seats to provide thermal mass, however solar heat transfer would be inefficient in that configuration and it would represent a great deal of dead weight on the chassis. I subsequently decided, for reasons previously explained, that a header tank for the cold water system will be an important component, however combined with the hot water cylinder and under-seat tank(s), the all up weight just for these water filled components will be excessive, around 700kg. It would represent an adverse long term load on the chassis. Hence I have now decided to eliminate the under-seat water tank(s) which alone would contain 400 to 500 litres of water and thus weigh more than 400 to 500kg.

 

THE PENULTIMATE PLUMBING DESIGN

The steel header tank, if uninsulated and painted matt black, despite its smaller size (150 litres), could still confer good thermal mass, in addition to its primary function of providing the pressure head. However, is there a way to make this thermal mass even more efficient? My advisers from the Tiny House Company http://www.tinyhousecompany.com.au/ (Lara Nobel, Andrew Carter and Greg Thornton) suggested that a mid point stair configuration will be more space efficient than my original design with stairs at the west end. This new configuration in fact offers a number of improvements. As the header tank can now be located almost directly above the wood stove, it makes sense to take advantage of this arrangement to design a gravity/thermosiphoning circuit between the backboiler tank of the mini wood stove and the header tank.

Figure1Penultimate

This will effectively harvest heat from the wood stove, for later slow release of heat from the header tank after the fire is out. One danger of this arrangement may be overheating of the water in the header tank, however this can be avoided by always ensuring the tank is full of cold water before firing up the stove and by not running the stove for extended periods eg more than two hours. The intent here is to utilise the header tank water as thermal mass, and NOT to turn the (uninsulated) header tank into a hot water cylinder (the header tank will not and cannot replace a proper, dedicated hot water cylinder supplying the taps).

 

THE ULTIMATE PLUMBING DESIGN

The next natural question is whether it may be feasible to harvest heat from the wood stove to supply the hot water cylinder, while also using the same cylinder to gather heat from the solar thermal array, all by means of gravity thermosiphoning which, not requiring pumps or sensors, will be the most reliable and robust system possible. The answer is yes, however it will require particular design of the hotwater cylinder according to custom specifications. If you live in an area prone to frost, the heat transfer from the external solar thermal array into the cylinder must be indirect, via copper coils containing a glycol solution. Heat transfer from the backboiler tank of the wood stove to the cylinder can however be direct. Hence the hot water cylinder design should be as shown in Figure 2

Figure2CustomCylinderWithDualHeatSources

For adequate thermolayer separation within the cylinder, a tall vertical cylinder is best (rather than a squat horizontal cylinder).

 

It is essential to consider the requirements for effective gravity thermosiphoning which are:

  1. To drive a circulating convection current, the heat source(s) must be below the hot water storage cylinder, and the hot pipe must be relatively higher than the cold(er) pipe.

  2. Adequate flow requires minimum resistance within the circuit, which requires that the calibre of pipes be large (at least 28mm), that there are few or no right angle bends (gentle curves/bends in the pipes are allowable) and that the pipes should be relatively short (which requires close proximity between heat source(s) and hot water cylinder). Short pipes also minimise heat loss in transit (which is inevitable even with good pipe insulation).

  3. The higher the temperature gradient between hot and cold pipes, the stronger the convection current. Hence the intense heat from the backboiler of the wood stove will still enable effective thermosiphoning through a long circuit, whereas the less hot solar thermal array should have a shorter circuit to function effectively.

 

As such, my ultimate iteration based on these plumbing considerations is as shown:

Figure3Ultimate

Solar heating of water

In the "ultimate" version, there is no connection between the (cold water) header tank and the wood stove. For thermal mass purposes, the most efficient way to transfer solar heat to the header tank will be for this uninsulated matt black steel tank to sit directly against a double glazed window on the sun-facing aspect of the house. Obviously this surface area for solar heat gathering will be tiny compared to the volume of water in the header tank. Nevertheless, a modest five degree rise in water temperature within the header tank (eg 15degC to 20degC) will be excellent for thermal mass purposes. However 20degC will be completely inadequate as a source of hot water for the taps. The uninsulated header tank cannot and will not replace an insulated hot water cylinder as the supply for the hot water taps.

A dedicated solar thermal array feeding a dedicated insulated hot water cylinder is necessary for the latter purpose. This outdoor solar thermal array, if located directly in front of the hot water cylinder, could potentially suffer from shadowing from the timber deck (and its overhead awning) in the morning, hence the array may be better located toward the west end, despite the slightly longer pipes required (which of course must be heavily insulated).

 

Passive Solar Heating of the composting toilet:

Proper composting of faeces to kill pathogens requires high temperatures and adequate duration of composting. High temperatures can be naturally achieved by exothermic reactions within a large mass of decomposing waste, however the volume within the bin of the composting toilet is way too small to achieve this. Hence to speed up the initial decomposition of such a small volume, it makes sense to enlist passive solar heating. It is therefore important to locate the composting toilet on the sun facing aspect of the house, immediately adjacent to double glazed frosted windows. Indeed, now being located at the north western corner, the toilet will receive heat from the evening sun as well. Obviously when one is using the toilet, the frosted windows will be blocked off by pull down modesty screens.

Full time use of the Nature's Head composting toilet by a couple may require that it be emptied once per month. Minimal composting will have taken place by then (indeed no decomposition of freshly deposited waste will have occurred). Odour is actually eliminated during active use of the toilet primarily by means of dehydration (continuous ventilation) and coverage with sawdust/wood ash. Fresh compost within the full bin (now removed from the toilet) will be sprinkled with fresh water, because additional moisture will be required for further aerobic decomposition. The bin will then be transferred to an outdoor "solar storage" greenhouse chamber where it will undergo further passive solar heating for a month, by which time the waste will be truly innocuous. Further composting will need to be conducted by emptying this bin onto a larger composting mass the size of, say, a rubbish skip (with a rainproof lid). The month old compost will deposited on the top of the larger, older mass of compost. The oldest compost (perhaps two years old) can be harvested from a cutaway opening at the very bottom of the skip. This biologically safe compost can now be scattered at the base of trees.

 

General comments:

  1. Uneven weight distribution in tiny house: there is significantly more weight from the header tank and HWC on the sun-facing side of the dwelling despite the fridge and washing machine being on the opposite side. This should not be an issue if the weight (when parked) is not borne by the tires but by jackstands or footings (important to locate jackstands or footings not only at the corners but also under the mid point of the chassis, thus directly bearing the weight of the header tank). This uneven weight will not be an issue during transportation when the water tanks are empty.

  2. Standard mains pressure in domestic taps is around 3 metres of water height. The same pressure can be achieved by locating the header tank outdoors, on top of the roof, which will however eliminate the possibility of greenhouse heating of this header tank. The pressure head will be lower if the header tank is located indoors on the loft floor, but lower flow rates can be overcome by using wider calibre pipes to the taps (perhaps twice the standard bore).

  3. Water overflow from the header tank should be directed to the exterior, proud and clear of the wall of the house, by means of a gargoyle poised above the kitchen window. Figure 4. This overflow will be visible through the window from inside the house, signifying that the header tank is full and that pumping of water up to the header tank must cease.

     

Comments on the "penultimate" design:

  1. In this configuration where there is connection between the woodstove backboiler tank and the stainless steel header tank via copper pipes, electrolytic corrosion of both tanks can be prevented by the simple application of a magnesium anode in the header tank. The advantage of this configuration is that it confers residual heating to the house after the fire from the wood stove is out. The disadvantage is that it does not heat water for the hot water system. However it will be easy enough to just boil a kettle and mix that with cold water in a bucket to obtain tepid washwater.

  2. If the header tank has a loose lid (and hence the water in the header tank is connected with the atmosphere of the house), and if this water is warmed excessively, it could result in copious condensation on the inside walls and windows of the house overnight. The way to prevent this is to construct the header tank to be airtight, however it will need to have a wide bore venting/overflow port near the top, which must be vented to the exterior, which will also allow the moist air to escape outside, via the gargoyle,

    Figure4gargoyle

    Comments on the "ultimate" design

  1. The vendor I sought who makes custom hot water cylinders, Trevor, specialises in copper cylinders. I am uncertain if the copper hot water cylinder and copper pipes connected to the steel backboiler tank will in the long term lead to electrolytic corrosion of the backboiler tank. Mark of Salamander stoves was unable to advise me about this, apart from saying that after five years of use (with copper pipes) he has personally not detected any problem in his backboiler tank.

  2. When the wood stove is fired up, water in the HW cylinder can easily become scalding hot, hence adequate care must be taken to dilute hot with cold water when operating the taps. Rather than depend on complex electronic sensors (which regulate the water temperatures in modern domestic systems), the philosophy in this design is to depend on simple common sense.

 

CONCLUSION:

In view of the above considerations, I am actually partial to the "penultimate" design rather than "ultimate" design at this time.

 

G. Chia March 2016

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Plumbing the Tiny House

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Published on the Doomstead Diner on February 9, 2016

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1 ColdWaterSystemOverview

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Plumbing the Tiny House

Geoffrey Chia, February 2016

This continues the series of articles by which we hope to empower readers to exit the "killing fields of the future" (the cities), to help you achieve and maintain a comfortable offgrid lifestyle for at least a couple of decades after TSHTF (assuming you have purchased sufficient spare parts for maintenance and/or are creative in your repairs). For example, solar evacuated tubes invariably break, therefore it will be prudent to purchase many spares, in addition to those in your working solar thermal array.

In this article I outline my plumbing preferences for my tiny house which, to say the least, is a little unconventional compared with "standard" arrangements. The plumbing here is specifically configured for my tiny house design which I have described in a previous article: http://www.resilience.org/resource-detail/2544932-building-a-tiny-house

2 ColdWaterSystemNoExternalTank3 ColdWaterToHotWaterConnection4 ConventionalSystemUsingMicroprocessor&Sensors

 

Preferences for the cold water system:

 

  1. A steel rainwater storage tank within the lounge (under the seats) doubles up as a thermal mass tank which picks up passive solar heat in the daytime. This minimises the need to operate the wood stove at night. The water in this tank (eg 500 litres) may not last long depending on the rate of use, hence my preferred configuration is a permanent connection to an additional external rainwater tank with capacity of perhaps 1000 to 2000 litres.

  2. In off-grid configuration, the 150 litre header tank is all-important feature and serves three main purposes: first and most important is that if a tap is accidentally left open, the greatest amount of water that can be lost is only 150 litres (even if a hot water tap is left open, the last 50 litres of water in the cylinder will not be lost because at the end there will be no pressure head left to empty the cylinder). If however the system is directly connected to a community shared large (eg 40,000 litres) water tank uphill, it will be possible to lose many thousands of litres. The second reason for a header tank is that the ritual of filling of this tank each morning, either by electric or manual pumping, will reinforce the value of fresh water and encourage daily limitation of water consumption (of course this is not true rationing because the header tank can always be refilled at any time, but being creatures of habit we will probably just fill it once a day or even on alternate days, thus limiting water consumption to <150 litres per day per tiny house). Thirdly, a header tank eliminates the need for a frequently operating electric water pump (triggered by the pressure drop detected by an electronic sensor whenever a tap is opened). It eliminates another layer of electronic complexity (even though a high volume electric pump is part of my configuration, it does not require any electronic sensor and also has a manual backup). Another purpose of this header tank is additional thermal mass.

  3. This system includes the option of direct connection to town (reticulated water) supply at normal mains pressure. This high pressure port will also be suitable for permanent direct connection to a larger water tank situated uphill, although as stated before this is to be discouraged.

 

The diagrams are self explanatory

5 TypicalHotWaterCylinder6 HeliatosVendorsDiagram7 Mini10EvacTubeArray

Preferences for the hot water system:

 

Contemporary conventional solar / hybrid hot water systems are highly complex and depend on sophisticated electronics. I initially describe my general preferences, then outline the workings of proven "standard" setups, then go through a process of deconstruction and simplification to pare things down to the bare bones system I personally prefer.

My general preferences:

  • I prefer solar heating of water with an evacuated tube system (the "heat pipe" type evacuated tubes, NOT the hollow core type) with no integrated gas or electrical backup. Evacuated tubes are more efficient in temperate climates in winter compared with flat panel arrays*. Best orientation is facing the equator (ie facing North if in the Southern hemisphere) and permanently angled around 15 degrees higher than your latitude eg if you are 40 degrees South, it should be angled around 55 degrees from horizontal, which is optimal for winter. Suboptimal angling for the summer sun is in fact desirable, to avoid overheating in summer.

  • If there are several overcast days, the wood stove (or LPG stove) can be fired up and hot water obtained from the backboiler tank or by heating a kettle. Adding the hot water to cold water in a bucket will create a comfortably tepid wash mixture. For me the expense and complexity to plumb a system which connects pipes from the woodstove backboiler (eg from the Salamander Hobbit system) to the hot water storage tank is not worthwhile.

8  Heliatos configurationWithTubeArray9 PassiveThermosiphoning10 PassiveExternalStandaloneSystem

Conventional systems:

  • Contemporary conventional domestic solar hot water systems use a microprocessor controller with electronic sensors. The "Heliatos" system http://www.heliatos.com/ obviates the need for microprocessor control of the pump. I have no pecuniary interest in Heliatos but mention them repeatedly because their components and configurations enable simplification of conventional complex solar systems (and easy retrofitting of non-solar to solar systems) while still working well, and I have had productive dealings with them previously. The key components are the "bottom feed connector" and a simple 12V DC electric pump + 10W photovoltaic panel. The standard Heliatos configuration assumes the solarthermal array is on the roof, ie above the level of the hot water cylinder, and the cylinder incorporates backup gas/electric heating. Typical cylinders operate at around mains water pressure. Whenever hot water is taken from the top of the cylinder, cold water under mains pressure replaces it at the base to keep the cylinder full, to enable ongoing sourcing of hot water from the top. The entire water mass in the cylinder is always kept hot because backup heating kicks in as needed, as determined by temperature sensors. Please note: all pipes containing hot water must obviously be heavily insulated, this is not shown in the diagrams for simplicity.

  • My modifications:

  • My modifications involve use of evacuated tubes rather than the Heliatos flat panels and placing the tube array on the ground rather than on the roof for ease of cleaning and maintenance (also easy to cover with a tarpaulin to shut down the system if it overheats or to protect against a hailstorm). Tubes are thus located at a lower level than the hot water cylinder. I also choose not to have backup gas/electric heating. The mode of operation is described on the diagram. Thermosiphoning during the day should be enabled, thus eliminating the need for an electric pump and PV panel.

  • My aim is to reduce complexity (resulting in only minor inconvenience) and thus ensure long term robust performance. This configuration is pretty much guaranteed to work, because there are already well proven "stand alone" outdoor evacuated tube systems which utilise passive convection currents, with the tank situated above the tubes. Such standalone outdoor systems are suitable for warmer climates such as Queensland but not ideal for cold climates such as New Zealand, where it is best to locate the hot water cylinder in a warmer indoor environment for greatest efficiency. I sought the opinion of the Heliatos consultant, Dr Abtahi (Phd) about my split system preference, who emailed me back that what I propose is not only workable, it is actually not uncommon. Thus I cannot claim any originality here and can be quite confident of its feasibility. His main caveats were that the pipes must be properly insulated and the array should be tilted so that the hotter end of the manifold sits higher, to kick start thermosiphoning in the morning.

  • It is always important to seek the advice of your local plumber, which I am also doing. We can expect problems to arise if the sizes of the tank and solar array are mismatched between each other and also with regard to the climate. For example of the tank is too big, solar array is too small and winter sun is too feeble, you can expect persistent poor heating performance. Conversely if the tank is too small, solar array is too big and summer sun is too strong, the system can boil away the water in the tank and cause the tubes to overheat. The good thing about "heat pipe" evacuated tubes is that one or more tubes can be removed from the array and the system will continue to function perfectly (obviously with less heating power). So you can reduce the array size in summer and increase its size in winter very easily. Alternatively simply cover one or more tubes if the day is too sunny.

 

 

11 ExternalHeatExchanger12 PassiveThermosiphoningThruInternalHeatXchanger

 

 

Frost

  • If frost is a likely problem, a glycol solution must be run through the manifold and this circuit must be kept separate from the domestic water. Heliatos have an external heat exchanger which connects to the bottom feed connector, hence if retrofitting, there is no need to purchase a hot water cylinder with internal heat exchange tubes. The Heliatos external heat exchange system requires two pumps and a 20W solar PV panel in the usual "high panel" configuration (compared with the standard Heliatos arrangement which uses one pump and a 10W solar PV panel).

  • If establishing your system de novo, obtaining a cylinder with internal heat exchange tubes will be preferable and more efficient. As the internal heat exchange tubes will be much wider than the tiny tubes of the Heliatos external heat exchanger (thus posing less resistance to flow), there should be no need for any electrical pumps at all in the "low panel" configuration. This arrangement may turn out to be the simplest yet most robust configuration, which can suit all climates (even with freezing winters), as seen in the final diagram. Hence this is my preferred configuration. As in all things the proof of the pudding is in the eating and the end user must try their own system out for themselves and tweak things if necessary to make it work. There will be different specifications of different components purchased by different users in different climates, hence no two systems are likely to be identical and some customisation may be necessary.

 

Exclusive use of rainwater will avoid the problem of lime deposits from hard water.

 

CONCLUSION: This article outlines a variety of options. Different configurations will suit different people depending on whether they want roof mounted or ground mounted panels and what level of complexity they are happy with. Conventional systems are convenient (hot water is available at all times with backup heating which however requires complex electronics) but also have more potential points for failure. I do not mind some inconvenience (no hot water in tank after several heavily overcast days) but prefer an easily maintained, simple and robust system with greater longevity. Just remember to buy good quality components from the outset and obtain plenty of spare parts (eg extra evacuated tubes, magnesium anodes etc) and you should be able to enjoy using the same system for at least the next twenty years.

 

G. Chia Feb 2016

 

*Footnote:

Boat based solar thermal arrays must by necessity be mounted flush on deck, which when stationary will be horizontal (or near horizontal), but due to boat movement will be constantly varying in angle. Evacuated tube systems are not feasible for boats because:

  1. Irrespective of latitude, the tubes need to be angled at least 20 degrees from horizontal to allow convectional forces to operate within the tubes

  2. Even though designed to cope with small hailstones, tubes are easily shattered (whereas a flat panel with polycarbonate cover will not break if a heavy shackle drops on it)

A boat based, horizontally mounted flat panel system will therefore require water to be circulated by electric pump: there is no option for passive thermosiphoning.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Mini Wood Stoves

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Published on the Doomstead Diner on January 29, 2016

KimberleyStove

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It's not Rocket Surgery: choosing an indoor mini wood stove

Geoffrey Chia, Jan/Feb 2016

 

As of 25 January 2016 at the time of commencement of writing this article, the cold spell affecting East Asia killed more than 65 people in the subtropical island of Taiwan. The temperature in Beijing dropped as low as minus 40 degrees C, however Northern China is used to dealing with heavy snow dumps and subzero temperatures in winter and hence coped better compared with Taiwan. The last time snow was seen in Taipei, the capital of Taiwan, was more than a century ago. The fact that Taiwan is a relatively small subtropical island, which we would expect to be dominated by the moderating effect of the South China Sea, makes this rare event seemingly even more bizarre. That is, until you understand the physics of how coastal and island provinces on the leeward (downwind) side of continents can often be dominated by continental rather than maritime weather, which I mentioned in my previous article "Location, location, location", where I compared Vancouver Island with Nova Scotia.

It is no coincidence that a record breaking monumental snowstorm also affected the East coast of the USA, the leeward side of the North American continent, at the same time as the cold weather affected East Asia. In general, at those latitudes; the windward (Western) sides of the continents, which are more dominated by maritime influences, are less prone to extremes of heat and cold than the Eastern sides.

Climate scientists tell us the peculiar combination nowadays during Northern winters of high temperatures in the Arctic regions and low temperatures extending to low latitudes, is due to the disruption of the circumpolar jet stream as a consequence of climate change.

One issue I did not mention in my "Location" article was the beneficial warming effect of the Gulf Stream on North Western Europe. The demise of the Gulf Stream appears to be a foregone conclusion as climate change progresses, following which North Western Europe can expect even worse cold spells in winter, even as the rest of the world heats up.

My "Location" article focused on avoiding heatwaves and managing fresh water supply. It did not discuss coping with cold weather (which well prepared humans can survive better than heatwaves). In choosing our future location, it is far better to settle where there will be low risk of heatwaves (despite the occasional cold snaps), rather than to settle where there will be low risk of cold snaps (but have high risk of terrible summer heatwaves). Most locations in our future world will face the latter situation in due course.

InStove60&100litreModelsThis article will focus on one item which can keep you comfortable in cold weather, especially when faced with the inevitable fossil fuel shortages in the near future: the indoor wood heater/stove, with special attention to the secondary combustion biomass (SCBM) heater/stove. It is not a comprehensive article but will concentrate on models which can be used in a caravan or tiny house, my particular area of interest.

The other important role of this biomass heater/stove will of course be for cooking. It will become an essential appliance when we face future shortages of kerosene and LPG.

Before we proceed, it is vital to mention the first three principles in dealing with cold weather: insulation, insulation, insulation (just as the first three principles in managing electricity use are efficiency, efficiency, efficiency). The well insulated tiny house, warmed by two people and a dog, may not require any additional heating because of the small interior volume of air.

Furthermore, in my particular tiny house design http://www.resilience.org/resource-detail/2544932-building-a-tiny-house, I incorporated an indoor steel water tank (under the lounge seats) which will provide thermal mass superior to (and lighter than) concrete.

Good insulation, small interior volume and thermal mass (heated by daytime passive solar influx) alone may enable you to go without active heating for most of the year, depending on where you live.

LiberatorHeaterOn the other hand, for adequate ventilation and to avoid condensation, it is necessary to allow some fresh (cold) air in and stale (warm) air out of the tiny house. In the case of the hermetically sealed modern Scandinavian dwelling, this is achieved (with minimal temperature drop) by a heat recovery ventilation system. For a less airtight dwelling in a less cold climate, sufficient ventilation may occur through "natural" leaks in your house (eg air coming in via the gap under the front door and out via a poorly sealed upper window), which will of course cause a drop in internal temperature. If you are installing a wood stove in your tiny house for future cooking anyway, this stove can double up as your heater and there will be no need for an electrically powered heat recovery ventilator. In this article I use the terms biomass and wood interchangeably, because 99.9% of the time, most of us use wood for our (non fossil fuel) stoves.

My criteria for the ideal biomass stove / heater for a tiny house are as follows:

  1. Must have exhaust flue / chimney – absolutely essential requirement

  2. Minimum use of fuel

  3. Minimum emissions

  4. Small and light

  5. Little need for constant tending

  6. Ability to monitor fuel and flame

  7. Able to source air intake from exterior

  8. Affordability

  9. Other issues eg aesthetics

Jotul(1)Criteria 2 and 3 can be summed up in one word: efficiency. The least efficient, most hazardous, most polluting and most wasteful heat source is an open fire. Next worst is the open brick fireplace. The standard cast-iron combustion box with flue is a good deal better but still woefully inefficient. Furthermore even a "small" cast-iron stove can easily weigh 150kg, which is quite unsuitable for a tiny house on wheels.

Even though the technology has been around for decades, we have failed to widely embrace the secondary combustion biomass (SCBM) stove, of which the "rocket stove" is the commonest design. Standard fires only burn the primary solid material of the biomass, releasing secondary combustible materials such as soot, hydrocarbon gases and carbon monoxide into the atmosphere, which can cause acute irritation of the airways and eyes, even poisoning or asphyxiation. If inhaled chronically over decades it can lead to emphysema and even lung cancer. These remain terrible problems in Third World countries. A stove designed to burn both primary biomass as well as the secondary emissions is far more efficient, causes far less pollution and is thus far healthier than traditional wood stoves. It needs far less fuel to do the same work (eg just a quarter of the wood normally used for a conventional stove), hence requires less back breaking physical effort chopping and carrying wood, hence also protects against deforestation. Additionally such a stove can reach much hotter temperatures. There have been great initiatives to introduce SCBM stoves (such as the InStove) for use in the developing world, if only for health reasons.

Bobcat-Rocket-StoveIf you google "rocket stove", the vast majority you find will be solely for outdoor use and will lack exhaust flues. Even those with exhaust flues may not be certified for indoor use (the commercial forces of our fossil fuel economy have long suppressed this market). Hence most "permies" these days are pioneering this option without official sanction.

Development of the "rocket mass heater" actually preceded invention of the rocket stove. This mass heater is a different beast, in that the hot metal components are enveloped in big heavy slabs of cob (or similar earthen or concreted thermal mass) to retain the heat for slow and steady release even after the fire goes out. The cob can be shaped in the form a comfortable warm bench. If used indoors, this mass heater is only suitable for a large, fixed, ground based dwelling, not a tiny home on wheels. Furthermore many rocket mass heaters may not incorporate a stove in their design.

With regard to SCBM stoves with exhaust flues/chimneys (which may or may not have been officially approved for indoor use) my websearches revealed the following types:

WEBSITE http://www.instove.org/60-100-liter-cookstove http://www.rocketheater.com/ http://www.bobcatrocketstove.com/ Unfortunately no longer in production
Size and weight Probably too big for most boats/caravans Probably too big for most boats/caravans Small (perhaps too small) and light
Need for constant tending +++
horizontal fuel port needs constant feeding
++
vertical fuel port, wood self feeds by gravity as it burns down
+++
small horizontal firebox needs regular feeding
Ease to monitor flame and fuel Easy Easy Need to open door periodically
Ability to source external air intake Maybe, but need to custom configure No ?probably yes
Cost in US dollars $850 for 60litre, $995 for 100litre ?$1500 (contact dealer) Unavailable
(?previously $400)
Remarks Mainly designed as a stove to cook for large numbers of people, cooking slots only fit custom sized pots Mainly designed as a heater. Sides of secondary combustion chamber can get very hot & pose risk of burns Add-on small water tank can provide thermal mass and hot water supply
Aesthetics Utilitarian Industrial Odd looking, may appeal to some

————–

WEBSITE Silverfire Hunter Stove Kimberley Stove/Heater
Size and weight http://www.silverfire.us/hunter-chimney-gasifier-stove https://www.unforgettablefirellc.com/
Need for constant tending Small and light Ideal size for boat/caravan
Ease to monitor flame and fuel ++
"batch feed" wood vertically
can burn slowly overnight without tending
Ability to source external air intake Need to remove pot to view status of wood and flame The only SCBM stove with viewing window
Cost in US dollars No Yes
Remarks $220.00 $3750 – 3995
Aesthetics When starting, large flames with smoke leap out of central combustion chamber. Pots and pans get coated with soot from primary combustion By far the most expensive but also the best made
  Looks like a biscuit tin Classy

The above are mere impressions obtained from web searches, not based on any practical experiences of mine. Practical reviews from the manufacturers and customers can be found from amazon.com or youtube. This article is intended to spark (pun intended) interest in this topic so that the reader can do their own research and make their own decisions. One issue I have not yet looked into is the maintenance required for each stove type. Every setup will require periodic cleaning of the chimney.

silverfirehunter stoveBased on size and availability, the only two SCBM contenders for use in a tiny house on wheels are the Silverfire Hunter and the Kimberley stoves. Although the Kimberley is far superior in every way it is also hugely more expensive, however you generally get what you pay for. It is false economy to buy a cheap stove if your house ends up burning down.

The Silverfire Hunter is described as a "toplift updraft" or TLUD gasifier. It generates bare flames and smoke out of the central cavity at startup (secondary combustion occurs later in a ring around this). This issue may be a dealbreaker for the indoor user. During cooking, the base of the pot/pan is in direct contact with the primary flame, causing soot deposition. An optional cast iron disc cover is available to minimise this, although it will also reduce heat transfer. One reviewer wrote that it needs frequent ash removal which requires it be disconnected from the flue, taken outdoors and turned upside down.

For those still keen on mini wood stoves of standard design, the following review websites are helpful:

http://www.tinywoodstove.com/small-stove-reviews/

http://www.waldeneffect.org/blog/Smallest_wood_stoves/

As mentioned previously a small standard cast iron stove can easily weigh 150kg, however the tiniest models may weigh less than 25kg.

For tiny house purposes, two particular models seem especially suitable (mainly because I greatly value the ability to source external air intake):

Jotul 602: apparently more than a million of these have been made, hence one would expect all the bugs have been ironed out by now. H25.25” x W12.6” x D21.25” , costs around $900. Weighs 73kg, able to configure for external air intake. Apparently 75% efficient (?capable of some secondary combustion)

The Salamander Hobbit stove: http://salamanderstoves.com/the-hobbit-stove/

Size: 302mm wide, 272mm deep and 465mm high, the low emission version costs £525 pounds sterling.

Weighs 60kg, able to configure for external air intake. It is designed to enable some secondary combustion, although not as efficient as the purpose designed SCBM stoves.

 

CONCLUSION:

As in all things, your choice will depend on how you weigh up the various advantages versus disadvantages, as well as your individual circumstances. Many amateurs have cobbled together home-made rocket stoves for outdoor use, however few sane people will hazard home-made stoves for indoor use.

 

G. Chia Jan/Feb 2016

 

 

 

 

 

 

 

 

 

 

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