The hot water tank is a 300 litre stainless steel tank. Stainless steel is better at reducing stratification (minimising mixing) because it conducts less heat compared to copper. Different grades of stainless steel exist for different types of water (hard/soft). One also needs to check the type of welds used on the tank as some can not cope with certain water types.
The tank was modified to allow me to connect the solar PV water heating system (previous blog) in the future using thermosyphonic action i.e. hot water is lighter than cold water so it naturally flows from the top of the tank to the bottom (Reducing the need for pumps). The DC power from the solar panels will be connected to electric heating elements. As the solar power varies the heating elements will adjust the output power through a control unit I am developing.
IfI install a solar hot water system or another method in the future this will be done with a plate heat exchanger rather than a coil. I installed extra connections on the tank for this reason. The reason for the heat exchanger is that the tank will heat from the top down. A plate heat exchanger looks like the following
If one opts for a coil it creates turbulence while heating the tank. I found it difficult to find a tank manufacturer who will install the correct surface area of a coil for a climate like Ireland. I feel most are designed for hot countries like Spain where the sun shines and stays shining. If one opts for a coil rather than a plate heat exchanger one requires a large coil surface area to ensure that most of the solar energy transferred in the least amount of time and the temperature returned to the hot water solar panel is at a minimum. In this way the hot water solar panel can operate at its maximum efficiency.
Initially when researching the options available to plumb the house I came across two main methods- Pressurised/Closed or Gravity/Open. I settled for a gravity based system because of the simplicity, DIY, reduced parts and maintainability. If one can increase the height of the gravity tank the pressure will increase at the taps.
Below is a video of what a pressurised/closed system can do (if it goes wrong and probably very rarely). When I was researching pressurised systems I felt that there seemed to be different ways of designing these and providing the necessary safety levels. I do not like systems where there are potentially hidden failures (when a safety device is supposed to work and does not).
I also was hoping to use gravity to supply the showers but it is becoming more difficult to find a good choice of shower valves and shower heads that work on low pressure . The way around this to keep things simple is to install a shower pump in a central location for two of the showers (see below). One can then use a shower head that helps control the flow rate and keep the water use to a minimum.
For one of the showers I already have a shower valve and head that works well on gravity so I will plumb this separately directly from the tank (shower 3 in the layout below).
The plumbing layout for the house is shown below. (The toilets are fed from a separate gravity tank supplied by the rainwater harvesting system as shown on a previous blog.)
I am using Qual-Pex for the plumbing in the house. It varies in price so it is a good idea to shop around (The 1/2 inch varies from €70 to €200 for the same pipe). I ended up using 200 metres of 1/2 inch and nearly 50 metres of 3/4 inch and 25 meters of the 1 inch.
The overflow from the tank needs to be well secured or finished in copper to ensure that if the tank overheats the pipe will not sag/bend or cause a restriction.
The brass fittings are cheaper than the quick connect so I will use these. One needs a good plastic pipe cutter as using a hacksaw is not feasible. I used a Ridgid brand plastic pipe cutter and I am very happy with the quality.
With a plumbing design one needs to ensure that the size of pipes are no bigger than they need to be. One reason for this is that the volume of water in the pipe will cool down and one has to wait for this to run through fully before getting hot water at the correct temperature.
I calculated that 10 meters of 1/2 inch pipe holds approximately 1 litre of water and 10 meters of 3/4 inch holds 2.3 litres. This gives one an idea if a solution is required and the wait time.
The cold water pipes will be insulated as I am concerned that condensation could occur on the surface of the pipe.
I also tried to ensure that the number of connections/joints are kept to a minimum and I tried to place these only at accessible points.
Logistics of getting hot Water to the furthest points.
The kitchen sink hot water supply is too far from the tank so I may develop an on demand system that ensures hot water is available once certain taps are used rather flushing semi warm water down the drain and a one or two minute wait for hot water. Installing instantaneous heaters is not economical.
A way to solve this is only use one 12 volt pump and have a valve at each sink position. This pump will then feed into the gravity header tank rather than the hot water tank (I need to check the regulations) . I want to keep the plumbing connections and electrical devices to a minimum. The power to operate this can be a small solar panel charging a battery.
The plan is to develop a solution around the following -Measure the hot pipe feed temperature, Detect if the tap is going to be used and link this to controlling the pump and valve.
The only item that needs to be purchased is a 12 volt pump and a 12 volt valve and develop the control unit to suit the Irish regulations. I have started on the design of this. In the meantime I will install a third pipe in the bathroom and kitchen for the final solution.
As discussed in an earlier blog I will use the rainwater system to feed the toilets and one outside tap. I have started to install the pipework internally . This involves running a 1/2 inch pipe to each toilet. I note that the Drainage and Waste Water Disposal building regulations state that the pipe used must meet the following-“ for rainwater green / black / green bands and the words RAINWATER in black lettering“. I rang around and no one appears to stock this in Ireland. I note it is available in the UK. Instead I have marked the pipe with permanent marker in the above colours with the words RAINWATER. An image is shown below.
The planned schematic of the rainwater system is shown below.
I note that some rainwater systems top up the main tank in the ground if one runs short of water in the summer. I have opted for the header tank where I can manually top up this smaller tank with fresh water or let it automatically bring fresh water to the tank for the duration of the drought with the control unit I built. I feel that topping up the main tank with fresh water is more wasteful.