The fire is in

The fire is in & has been lit to see if it’s all OK and also to help with any last drying out of the inside. Being mostly timber frame construction this is a lot less than a concrete building requires.

The slate slab under the fire is the first bit of final floor to be in the house.

Even with doors being left open the house was rapidly super warm with the fire. I know it’s not a cold time of year, but it does show how a well insulated and sealed house is easy to heat up and then stays warm.

2014-05-12 08.54.07 (2)

Digger Hydraulics

Compared to digging, smashing, bashing and moving material about by hand the hydraulics of diggers etc. on site is amazing.

Look at what this kid has done with syringes, and pipes. Maybe air not liquid in the pipes, but probably not.


Hot water heat recovery via the Thermal Store?

Instead of, or in addition to a heat squirrelhow about sending the domestic hot water (DHW) waste via a coil in the thermal store?

It should be easy to have a thermostat that checks if hot water being “thrown away” is above the temperature of the lower section of the thermal store, and if so, sends the water through a heating coil in the thermal store, so it passes over some of it’s heat before it goes down the drain.


  • water leaving the shower head at 42 deg C will have cooled to around 37 deg C by the time it gets to the drain.
  • The 5 deg heat loss will already have been recovered to the house (assuming effective MVHR on the shower room exhaust).
  • The heat squirrel holds 120 litres of hot waste water, to pre-heat any incoming cold water that is heading to the heat store.
  • By holding the hot water, there is more time for the heat transfer to any incoming cold water, especially any that sits in the coil inside the heat squirrel.
  • Hopefully this 120 litres of water is regularly self flushing as “grey water very quickly turns manky when stored, even for short periods.”

Hot Tub Hot Water Heat Recovery

One key thing here, is my plan to have a log fired hot tub.

  • I’m looking at hot tubs that use logs to get the water up to temp and then keep the temp there.
  • BUT to accelerate getting it up to temp after it has been left a while, I want the option to top it up with hot water from the domestic hot water supply.
    • Reading elsewhere, hot tubs tend to run around 36° degrees.  Although friends with hot tubs say they tend to run theirs between 37° degrees and 39° degrees.
  • I also want the option of taking water from the hot tub, when it’s not going to be used for a while and sending this via a heat recovery option back to the heat store.
    • I accept that sending “lumps” of less than 120 litres at a time will optimise this in terms of giving the water time to transfer it’s heat to the heat store / cold water coming in to the house.

Thermal Store

This is part grabbing historical Thermal Store notes to one page, and part adding new notes.

Click here for notes on Thermal storage – pros & cons.

Looking at the Akvaterm thermal stores (which can go up to 5,000 litres !!)


  • have a stratification baffle plate about a third of the way down the tank. (see photo below). This can be optionally upgraded to an insulated baffle to further improve performance but the added benefit is not huge as it is very good already.
  • Once the water above the baffle has been heated to a high temperature by the heat pump (50ºC-60ºC) it then shifts to heating the bottom two thirds of the tank to a much lower temperature suitable for underfloor heating (around 40ºC).
  • OR if / when the heat pump is generating lower temp water (often more efficient COP) it only targets the bottom section.
  • larger than normal lower domestic hot water coil. This is to ensure that the incoming mains water picks up as much heat from the bottom of the tank which holds the ‘cheaper’ heat produced at a high C.O.P.


The AKVAir Solar Plus is available from 300-2000 litres and is 3 bar pressure rated. The tank has 4 coils, two for solar input and two for domestic hot water (DHW) and is divided by a baffle plate, approximately 60% below and 40% above the baffle. Each section contains one solar and one DHW coil and all coils are positioned vertically.

The AKVAir Solar is available from 300-2000 litres and is 3 bar pressure rated. The tank has 3 coils, one for solar input and two for domestic hot water (DHW).


Akva Solar plus coils diagram   Akva Solar diagram key

Akva Solar Plus coils + baffle plate     Akva Solar Plus coils






  • AKVA GEO is suited to all heat sources (others seem to be solar or something specific).
  • example layout:




Heating System Schematic

Dual Cylinders?


  • For larger domestic and commercial projects, our dedicated heating buffer cylinders are used in conjunction with our high-gain unvented cylinders to allow greater variation between heating and hot water demand.
  • The separate low-temperature heating buffer allows the small, infrequent heating demands of a property that is “up to temperature” to be met by stored renewable energy before activating the heat pump/boiler to reduce wasteful on/off cycling.

An alternative Hot Tub

I’ve thus far been considering a Dutch Tub hot tub:

  • I think they look cool
  • Their water volume is “only” about 650 litres, so not too much to heat up and keep walm. Also not too much weight.

BUT their size does mean while they are super comfy for 2 people, as soon as you go over that, it gets a bit of a squeeze. (the bottom of the Dutch Tub tubs domes up).
Look at these 2 pic’s of 1 and 2 people in a Dutch Tub (there is only one size). Click on either pic and you’ll get the full size version where yu can see toes at the other side of the tub and arm spans etc.

dutchtub-2_people    dutchtub-1_person

I’ve just found Cashen Hot Tubs. Their tubs are 100% made from timber from local (Cornish) forests. Mostly from Dutchy controlled forests less than 6 miles from their sawmill.

They come with a wood burner heating option that looks the same as the hot tubs I was in at last years (2012) Nova Festival:

Wood fuelled hot tub at Nova Festival 2012


The 1.7m diameter Cashen hot tub is down as suitable for 4-5 people. It’s about 400 kg empty, so add the 1,800 litres of water, the burning fire and a few people and you rapidly get to 2,500 kg or a bit more.

  • The inside depth of the tub is 920mm, outside height is 1090mm. They have said they can make a shallower tub to make the most of your sea view. But will that mean cold shoulders ?
  • They can also add a filtration system to the wood fired hot tubs.

Below are some photos and other info from the  Cashen Hot Tub Website and some emails from them (so accurate early 2013):

Wood Burner Hot Tubs (Elec heated a bit more £)
1.5m (4.5ft) dia. 1,600 litres seats 3-4 people £3,125
1.7m (5ft) dia. 1,800 litres seats 4-5 people £3,475
1.9m (6ft) dia. 2,500 litres seats 5-6 people £3,725

The tubs have an “inside depth of the tub is 920 mm, outside height is 1090 mm. If you were interested in a shallower tub to make the most of your sea view, this could be accommodated.”

Prices include our eco-friendly underwater wood-burning heater and integral seating as standard.

The stove is made from marine grade aluminium. They can be replaced at £800.

Hot Tub Optional Extras
Wooden Steps (I assume external to get in and out !) £195
Lift off wooden cover £265
Lift off custom made insulated cover £350
Pipe work screening
– which it looks like the Nova Festival tubs had. The Cashen photos below show tubs without a cover over the pipe work.
Filtration system £515
Stainless steel finish for chimney £180

Water Temp & Stove Size

Reading elsewhere, hot tubs tend to run around 36° degrees. The stove needs to be sized to not over or under heat the size of the tub.

Hot Tub Placement & Maintenance

The more they are not left the better.

“Use it and wash it regularly, another important thing is to make sure the is adequate air circulation underneath the tub. There is no problems using sea water in the tub as the stove is a manufactured of marine aluminium, the actual barrel itself works better with salt water as it keeps the moisture better and it slows down the dry out process.”

Photos from the Cashen Hot Tub Website:









From another Website:

wood fired hot tub - schematic

Sewage treatment

Although the main pipe that goes from Perranporth to the sewage treatment plant by Cligga goes past the front of the house, that is under pressure and isn’t a pipe we can discharge into.

At the moment Silver Spray is a soakaway !

So, as the house is being “upgraded” we’ll be fitting an on-site sewage treatment plant. These treat the toilet waste and to a level where the water meets the rules to be discharged into the groundwater.

This is what the neighbouring properties all have.

Next door to the east, Ramoth have a Klargester BA 450 BioDisc (now part of Kingspan Environmental) unit, that was installed by Dorset based Environmental Drain Services Ltd.

Talking to Environmental Drain Services:

  1. As it’s a treatment plant and not a septic tank the 7m minimum distance from a habitable dwelling rule does not apply.
  2. You need to be able to, on-going, access the lid to get into it. So you can build decking etc over it, but you can’t stand, drive or put earth over it.
  3. We should be able to rely on the percolation test / survey done for Ramoth way, as this is just next door. It’d be very unlucky for this to not be indicative of the Silver Spray ground.
Talking to Mark at Ramoth, there is not only the Klargester unit, with it’s small power supply, but the outlet feeds into a series of underground trenches, that in their case are closer to the house than the Klargester. These trenches are rock filled to help the distribution of the discharged treated water.


New “Dutchtub Wood”

The DutchTub team have created a version of their “tea cup” hot tub that is encircled by wood, which might look better for Silver Spray.

I asked and “Indeed, the Dutchtub wood has the same inner shape as the Dutchtub Original.”

The original Dutch Tub can weigh 1400 kg / 3000 lbs when full of water and 4 people. They suggest a small platform under the tub can spread the total weight on more square meters than just the four legs of the tub. ”


  • Length: 170 cm/67 inch
  • Width: 234 cm/92 inch
  • Height: 82 cm/32 inch
  • Weight: 85 kg/187 Ibs
  • Capacity: 650 liter/171 gallon
  • Material: 
    • Glassfibre polyester (RAL 7003, single color option)
    • Stainless steel
    • Preserved wood
  • Additional: This design is developed in collaboration with Feather Down Farm Days®
  • Delivery: The Dutchtub Wood will be delivered with a fire basket for the spiral, a special wok, a fire shield, a turbo connection for fast heating and a fiberglass cover
  • Check out the accesories.

Appliances generating the most CO2 by 2016?

I’m not sure I’ve got this right, but I think the post means that a 2016 built house (if to the regs !) will have the main areas of CO2 emmissions in order of magnitude as:

  • appliances (49%)
  • space heating (22%)
  • water heating (11%)
  • pumps and fans (10%)
  • lighting (8%)

So I’d better get those best rated appliances and building control systems for the kitchen and elsewhere.

Some updated Thermodynamic heating system info

I’ve come across the GreenServeUK website with new info on the Thermodynamic Panels.

There’s a big FAQ at

How it works from

Step One

The environmentally friendly refrigerant liquid is fed into the veins of the solar collector.

This refrigerant (R134A) has a boiling temperature of -25°C. The panel absorbs the heat from the environment and raises the temperature of the refrigerant.

The liquid absorbs the heat and it vaporises into a gas which increases the pressure.

Thermodynamic Panel Dimensions are h 800mm, l 2000mm, D 20m.
Each panel is about 8 kg.

Step Two

The hot gas is then passed through a compressor where the pressure causes it to heat further.

Step Three

The heated gas is then passed into the heat exchanger where the heat is transferred into the water cylinder.

Step Four

The cooling gas then passes through a valve reverting back into a liquid where it runs back into the panel where the process begins again.

The system is a solar domestic hot water system in which the solar loop operates on a similar principle of a heat pump.

It is composed of:-

  • An unglazed heat absorber  (1) with 3.20 m2 total aperture area.
  • An insulated,  hot water thermal store (200 l) (2)
  • A  thermoblock, which comprises the electrical powered compressor (5), the thermostatic expansion valve (7), the electrical heating element (4) and the controller.
  • Heat transfer fluid (refrigerant R134a)

The heat transfer fluid in the solar loop is the refrigerant R134a.

The refrigerant is passing through the absorber and evaporates while collecting energy from the surroundings.

The evaporated refrigerant is sucked by the compressor which raises the pressure.

In the condenser, which is integrated as an immersed solar-loop heat exchanger in the lower part of the store, the refrigerant condenses while transferring its condensing heat to the domestic water in the store.

Before the refrigerant is returning to the absorber, a thermostatic expansion valve is reducing the pressure.

An electrical heating element is located in the lower part of the store at the height of the solar-loop heat for use in emergencies and for the anti-legionnaires system.

The magnesium anode (8) or sacrificial anode will extend the life of the tank.


Hot Water Heat Recovery Options

It looks like there is a new player in the UK market. OR one that I’d not previously spotted!

They have a good few shower tray / under shower options and those that can be more centrally integrated into your whole property hot water system.


Our most popular waste water heat recovery system due to it’s great efficiencies, low price and superb all round performance. Ideal for new build applications, this product is sure to deliver results, whatever your criteria.

Recoup Tray+

Our tray is the perfect solution for apartments or ground floor en-suites. Achieving code in city apartments without renewables is notoriously difficult; this shower heat recovery system with flexible tray size is the answer that doesn’t cost the earth.

Building a wet room or have access issues? The Recoup Drain+ provides a great option. Finished in stainless steel and offering 50% efficiencies, this is a must have system for your self build or walk-in shower.

This compact WWHRS is easy to install, easy on the pocket and easy to maintain! As it’s name suggests, it’s ideal for retro-fitting in domestic and commercial properties. A very cost effective way to achieve efficiencies of up to 22%.

A system with great efficiencies specifically designed for large developments with good water pressure. This single walled exchanger provides up to 68% efficiency, so will tick a box for the Technical Director or architect looking for a cost effective solution to achieve code.