Instant hot water heater in series with solar

[Monomial]

I would like to install an inexpensive thermosiphon solar hot water heater (<20k baht) in my house, but still have an electric boost capability without paying the exorbitant prices they want for solar heaters with integrated electric boost.

Honestly, 90% of the time the solar heat is going to be more than enough all by itself. So we are really only talking about a solution for the small percentage of time where it rains for 5 straight days while simultaneously being unseasonably cold. Thus, spending tens of thousands of baht to get a solution for the margins not only defeats the purpose of the cheaper solar install, it also would seem an inefficient use of funds.

That said, how do multipoint tankless hot water heaters in Thailand respond when the inlet temperature is 90C? Do they use electronically controlled thermostats to turn off the heating element and silently pass the water through even at very high flow rates, or will they simply engage the heater all the time when the flow rate is high enough like a politician approving a corruption deal? I think it goes without saying that water boiling before it reaches the tap would be a bad thing.

The primary applications for the hot water are showering, running a dishwasher and clothes washer, and filling a whirlpool bathtub. While showering is not a particularly demanding task, the others require very hot water, and the bathtub in particular requires a very high flow rate (1" piping will be used). Has anyone ever done this before, and do you have any advice on models that I should consider?

Thank you for any assistance.

[Crossy]

Most instant heaters have a maximum inlet temperature around 50^oC, so if your solar is getting that hot you'll need to arrange some sort of bypass for the heater which you can close when you want to boost the water temperature.

The more expensive units have thermostats and do actually control the outlet temperature, the cheaper ones just fire up the heater when the flow rate is hight enough.

All will restrict the flow enough that your 1" pipe will trickle

[Gsxrnz]

Have the water from the solar system as your main supply to your hot water outlets. If it runs as high as 90 then you'll need to mix it with a direct cold supply.

Run the main feeder pipe close to the heater and just install a bypass system with appropriate valves that re-direct the water through the heater and then to your outlets

So normally, the water won't even go through the heater at all. When your solar isn't doing the job, open/close the relevant valves so that the water runs through the heater.

Bob's your uncle.

[fredge45]

Get a large tank (250+ liters) on your solar system. Be aware of when you see cool temps and cloudy days and become frugal in your hot waer use then.

Crossy is right about the trickle you will get out of a water heater regardless of how large your feeder pipe is. The heaters generally have inlet/outlets no larger than 1/2".

[ban muang farang]

Your solution is a open vented thermosyphon system with a heat exchanger. It takes time and effort to construct but can be done really cheaply. Be very very careful with a homemade circulating solar system. Without the appropriate pressure, temperature relief and safety valves you will basically create a bomb. You will also get water so hot it will most likely damage your plumbing and tapware or will scald you unless you install a high performance tempering valve which are unavailable in Thailand. Using this system will not create any pressure or flow restrictions and you will not need a huge supply pipe for your bath. Now as for your boosting system. This is the expensive side but it works.. you need to fit a continuous flow LPG hot water service as a booster for your heat exchanger with a thermostatically controlled pump to increase the temperature of your heat exchanger when the sun is not shining.

[ban muang farang]

Your solution is a open vented thermosyphon system with a heat exchanger. It takes time and effort to construct but can be done really cheaply. Be very very careful with a homemade circulating solar system. Without the appropriate pressure, temperature relief and safety valves you will basically create a bomb. You will also get water so hot it will most likely damage your plumbing and tapware or will scald you unless you install a high

You can make a pressure less solar hot water circulation system. Then there is no risk for over pressure.

I made one ten years ago, and is still working without any problem.

Arjen

i didnt say you can't make a pressureless system,thats is how i explained my system. Is your system completely closed? If so you must have some form of relief for thermal expansion. Can you explain how you have set it up?

[IMHO]

There are some reasonably priced solar hot water systems around....

We paid 37,800 for a 150L pressurized system with inbuilt 1500W heater, and 43,200 for a 200L version of the same.

We very rarely need to turn on the breaker for the electric heater though - only when we have a house full of people, and the capacity of the systems just isn't enough - more so than the water doesn't get hot enough.

[Monomial]

Thanks for all the input and ideas. I reflected for a while on everything said here, as well as my own independent research. In the end, I think I have found the most cost effective solution, but I would like to know if anyone has an alternative source to buy it.

Based on a preponderance of recommendations, the cheapest and easiest solution to the problem seems to be to get one of these:

http://wholesaler.alibaba.com/product-detail/brass-3-4-diverter-valve-for_1951475577.html

The link also show a thermostatic mixing valve in the picture to regulate the temperature down to 60C, but I think I would probably go without this, or at least only include it once I had already tapped off for my dishwasher and washing machine. Since this is only 3/4" instead of a 1" valve (they don't seem to have a 1" valve for this application) it will restrict the flow somewhat, but I have accepted that I am going to have to compromise if I want to save on cost.

My issue with this is that I don't particularly relish the idea of giving my credit card information to a random Chinese company on Alibaba. Does anyone know a local supplier for a valve such as this?

[ban muang farang]

http://pacificvalves.com/heatguard-ultra-high-performance-tempering-valve-au-standard-rmc This is the high performance valve you require. It is designed specifically for solar applications. You can order online from Australia,probably a safer bet than giving your details to a dodgy Chinese site.

Edited December 19, 2015 by ban muang farang

[IMHO]

There are some reasonably priced solar hot water systems around....

We paid 37,800 for a 150L pressurized system with inbuilt 1500W heater, and 43,200 for a 200L version of the same.

We very rarely need to turn on the breaker for the electric heater though - only when we have a house full of people, and the capacity of the systems just isn't enough - more so than the water doesn't get hot enough.

Water from around 45 degrees si for the most to warm for a shower, and for nearly everyone to warm for a bath.

Even in rainy season my warmwater system produces water what is warm enough for a comfortable shower.

I'm not sure it even needs to be 45c - my pool feels like a bathtub at just 35c

Anyways, not much you can do when you have 15+ people showering and washing clothes with hot water - the amount of cold water rushing into the tank beats the amount of hot water coming out

[sometimewoodworker]

http://pacificvalves.com/heatguard-ultra-high-performance-tempering-valve-au-standard-rmc This is the high performance valve you require. It is designed specifically for solar applications. You can order online from Australia,probably a safer bet than giving your details to a dodgy Chinese site.

Interesting that you also link to a Chinese website!

Pacific Valves International Co., Ltd (PVI)

Unit 603. 6/F, International Plaza, No. 20 Sheung Yuet Road, Kowloon Bay,

Kowloon, Hong Kong.

[Crossy]

If you go through AliExpress they have a good escrow system which holds your payment until you confirm goods received.

Never had an issue with them.

[IMHO]

If you go through AliExpress they have a good escrow system which holds your payment until you confirm goods received.

Never had an issue with them.

Agreed, have bought lots of stuff from Ali Express. Just don't pay extra for DHL - or you really will pay extra to the tax man, and additional tax processing fees from DHL on top.

Edited December 22, 2015 by IMHO

[Jing Joe]

On 20/12/2015 at 0:38 AM, Monomial said:

My issue with this is that I don't particularly relish the idea of giving my credit card information to a random Chinese company on Alibaba. Does anyone know a local supplier for a valve such as this?

As someone else pointed out, looks like they are a Hong Kong address.

I'm always confident using Pay Pal because I'm sure I  have to verify with my bank first for the payment to go through.