Hot Spring ground source heating

[AllenCherry]

Anyone who help?
I have access to a hot spring, temperature of the water is 50 - 55 deg C and the flow rate is 4 litres per minute.  The hot spring is actually inside the house.
Can this be used with a heat exchanger to heat radiators in various rooms?
Will a heat pump be needed?
Any advice will be very gratefully received,
Thank you in anticipation,

Allen Cherry

[Dave Jones]

crikey sounds awesome.

 

can you rig up a smallish pump into a a 3 port valve connected to heating and your hot water so you can have both ? Small central heating pump ? Just have to sort out if its got any gremlins in iut that will furr up your pipework i guess ?

 

Basically treat it as a free ASHP just missing a pump.

[JohnMo]

What heating system and hot water cylinder do you currently have?

 

What flow temp do you have going through the radiators?

 

What is your house heat loss (or build date and insulation levels and size)?

[Conor]

fantastic topic.

 

Answer is, yes, of course.

 

buy HOW is the interesting bit.. I doubt there is anything off the shelf that you can order and have installed. Whatever it will be, will be cobbled together and will require a bit of trial and error.

 

First, one has to assume that the water is non-potable, hard and corrosive. So pipework will have to suitable and you must maintain adequate separation from you own system. You wont need a heatpump. At a guess, making some assumptions:

 

cap the spring, divert the artesian flow (lets assume 1bar) through some suitable pipework, divert part of this through  a sized plate heat exchanger. Outlet of the heat exchanger re-joins the main flow-to-waste for the spring.

 

On the receiving end of the heat exchanger, you have it filled with something like glycol, and have a circulation pump running on demand to the main coil in your hot water cylinder. So this would in effect replace you normal boiler. 

 

you'd want a larger, thermal store so the same source is used for heating and hot water. You will need 400l of 50c water as the recharge time will be quite slow based on the 4l/m well flow rate.

 

[ProDave]

3 hours ago, AllenCherry said:

Anyone who help?
I have access to a hot spring, temperature of the water is 50 - 55 deg C

My no 1 question is WHERE are you?  I would be very surprised if this is in the UK.

 

Can you have the water tested?  if it is not corrosive, why the need for a heat exchanger?  just pump(s) and 2 or more 2 port valves.  Use a heat pump hot water cylinder with a large area input coil.

[sharpener]

1kW is 860 litre - degrees per hour.

 

So 4 litres/min x 30 deg x 60 = 7200 litre -deg / hr = 8.4 kW free heat for space heating, lucky you.

 

I would definitely use a heat exchanger, suitable for the water analysis of the hot spring, and put the whole flow through it after a fine mesh filter e.g. a 500 micron Y-strainer or a Magnaclean. Also fit isolating valves and a bypass valve so all can be taken out of service for maintenance.

If the water is acidic (quite likely) then you would need a nickel brazed HX which will be expensive. And de-zincification-resistant (gunmetal) valves and fittings on the primary side. Then put inhibitor (not glycol) in the secondary circuit esp since you have rads not UFH.

 

Use an S-plan or 3-way diverter setup for the HW. As you have a low delta T you would want a high-gain or HP type with large coil area. 8.4 kW will heat 240l/hr from 15 to 45C if you have a big enough coil so, depending on usage pattern, heating it in the small hours once a day might be enough.

 

Edited September 10 by sharpener

[SteamyTea]

You could knock up your own test heat exchanger.

A simple pipe in pipe design would give you an idea of how much energy, and at what temperatures, you are likely to actually get.

[Alan Ambrose]

I’m guessing NZ?

 

FYI Mine water could heat thousands of Welsh homes:

 

https://www.bbc.co.uk/news/articles/c0l867k70p8o

 

Between. 10 & 20C though. That doesn’t sound so encouraging .. according to PHPP my average ground temperature in 9.6C.

[AllenCherry]

Wow!  THANK YOU everyone for all the help!

 

A bit more information - the house is in the countryside of Japan (Myoko), and has no 'central heating' at all - heating during the winter is by a few paraffin heaters, gas and electricity in each room.

The hot spring water flows into a 'holding tank' before filling the hot spring bath (a Japanese 'onsen'), and I was considering using a stainless steel heat exchanger immersed into the 'holding tank' - something like:

https://www.cotswoldkoi.co.uk/product/submersible-stainless-steel-heat-exchangers/?attribute_size=Large+30kw&gad_source=1&gclid=CjwKCAjwufq2BhAmEiwAnZqw8hz-OZ0nZzfeIwPXz-Yf88Oxf4soCF1pnL5h-Lfiwm6P1luhYeXrJRoC9yUQAvD_BwE

The spring water does have some sulphur content, but is not very corrosive - so the stainless steel for the heat exchanger should be OK.

Given that the water circulating around the radiators will obviously be less than 50 deg C, how do I work out the size of the radiators for the room size?   The house is well insulated  - the Japanese do things correctly!

Another problem is the mains power is 100 volts 50Hz AC - so pump selection may be difficult.

Can anyone give some ideas on the piping to use - will plastic be OK?

Presumably an expansion tank will be required for the circulating central heating water, and the water will have to have anti-freeze added.  Is a 'header tank' required, or can it be a closed-loop system?

 

I really am appreciative of all the help - and yes, it is an exciting project, but I am an electronics engineer, not a central heating engineer!!

 

Thank you,

 

Allen

[sharpener]

4 hours ago, AllenCherry said:

Given that the water circulating around the radiators will obviously be less than 50 deg C, how do I work out the size of the radiators for the room size? 

 

You would need to do a proper heat loss calculation using e.g. the free Heatpunk app from Midsummer Wholesale. It will then guide you to correct rad sizes for the flow temp. (If you had got radiators already then upsize them by 1.9x for 50C flow).

 

4 hours ago, AllenCherry said:

I am an electronics engineer, not a central heating engineer!!

 

I am too, you will be in good company here. Electronics Engineers seem to have a better grasp of pressure, flow, thermal resistance, heat transfer etc than most plumbers bc all quantities have analogues in electrical engineering.

 

4 hours ago, AllenCherry said:

I was considering using a stainless steel heat exchanger immersed into the 'holding tank'

 

With a limited heat source (max 8.4 kW as above assuming you could transfer it all to the target rooms) I think you will only get half of that into the load (think load matching/load lines). So as an inspired/informed guess you will be best off picking a heating flow temp midway between the two i.e. 35 deg. The larger model is rated at 30kW with "approximately" 50K delta T, so 4.5kW at 15K which is v close to what you want. This might just be enough for a small well-insulated house but will require very big rads.

You might be better off piping the hot water into a conventional HX bc then you could have a proper counterflow arrangement which will be more efficient from the thermodynamic point of view. The secondary flow temp will then be closer to the source temp, and the waste spring water will be closer to the return temp from the rads, so you harvest more of the heat available from the spring.

@JamesPa has done quite a lot of modelling of this kind of thing so may have some more insights (or may be able to demonstrate I am completely wrong!)

 

Fascinating project, ATB with it.
 

[AllenCherry]

Hi Sharpener,

 

Many thanks for your comments!  You mention:

>> conventional HX <<

What do you suggest as a 'conventional heat exchanger'? 

From what I see, all other heat exchangers appear to need a pump for both the primary and the secondary circuits - would the pump on the primary side need to be 'rather special' to withstand the slightly acidic nature of the hot spring water?

 

Thanks for your help,

Best wishes,

 

Allen

[sharpener]

23 minutes ago, AllenCherry said:

What do you suggest as a 'conventional heat exchanger'

 

Flat multiplate HX like these, have heard good reports of inhouse SWEP brand by these people. Quite widely used in UK domestic HP installations so stocked by some plumbers' merchants here.

 

33 minutes ago, AllenCherry said:

would the pump on the primary side need to be 'rather special' to withstand the slightly acidic nature of the hot spring water?

 

Note their pH 7.5 to 10 limits for ordinary copper brazing, and get water properly analysed for sulphur content and other things as well. I have found test strips are not reliable (especially for pH measurement) on naturally occuring waters e.g. my harvested rainwater. Universal Indicator drops like these are OK and more sensitive.

 

Check with pump mfr but an all stainless steel/plastic construction would probably be OK as no intermetallic effects.

 

My rainwater is slightly acidic even after treatment but s/s pump shows no corrosion. (However 2 have failed for other reasons, cracked plastic impeller shroud and failed shaft gland, don't buy Stuart Turner! They consider them non-repairable so no spares available, but I have built one good one out of the bits from two. A bit like the old joke about why you need two Hasselblad cameras. /rant)

 

Of course if you have enough head available from the spring then ideally you would not need a primary side pump at all.

 

Forgot to add theory link earlier. Explanation here of why only half heat transferred, coil in holding tank will be an approximation to this.

 

HTH.

[JamesPa]

On 10/09/2024 at 04:55, AllenCherry said:

I have access to a hot spring, temperature of the water is 50 - 55 deg C and the flow rate is 4 litres per minute.  The hot spring is actually inside the house.

It might be worth taking a look at Icelandic heating sites where hot spring heating is common, as is pumping the hot spring water straight to the tap. When I went there for a holiday last year I got used to the smell of sulphur when I ran hot water.  Actually rather nice once you get over the shock.

[Alan Ambrose]

>>> don't buy Stuart Turner!

 

We have two ST dual monsoon pumps, one 30 years old, one 20. Both run off and on all day. No problems at all except for a few pressure cylinder replacements over the years. Last time one failed, I replaced them with cheap off-the-shelf vessels and they’re lasting well - last time was 10 years ago. ST had got a bit smart-arsed about the ‘maintenance kit’ costs. So, at least for that product, at that time, they were good.

[sharpener]

4 hours ago, Alan Ambrose said:

So, at least for that product, at that time, they were good.

 

Yes, a reputable brand, the UK-made ones are OK I think, my father had a little ST pump for a fountain in the garden which we brought in every winter. Which is why I was annoyed to find they did not do spares for the jet pump that had been installed by the rainwater system ppl for the previous owners but since discontinued.

 

When the first one failed (not their fault, garage flooded) I consulted their sales dept and was advised that the current model was ideal for the purpose. But when its shaft gland went they said it was imported from the Far East and just branded ST so only warranted for 1 year. I wrote to the Sales Director to argue this was not fit for the purpose described, but they would not budge and I had no choice but to pay for a third pump.

 

The shaft gland was a particularly poor design as the torque was transmitted through the flexible polymer bit and I think it sheared when trying to unstick the carbon/ceramic seal interface after not being used for some weeks. Eventually I found a replacement on ebay which also had a metal dog to transmit the torque.

 

The third failure was a crack in the plastic impeller shroud leading to a partial loss of delivery head which meant it did not reach the cut-out pressure. No obvious cause but equally annoying bc on their advice I had bought a new pressure control module which did not fix the problem. So I now have a working pump, a spare with a working motor and shaft seal but broken impeller shroud, and a spare pressure controller I do not need.

 

I will buy DAB next time.

[AllenCherry]

Thanks everyone for your help!

 

Please may I ask a few more questions?

 

If the ph of the spring water is virtually '7' (i.e. neutral), then will it be possible just to pump the hot spring water around the heating system?  If so, is there a suitable self-priming or submersible pump that could be used?  The top floor of the house will be about 25ft above the surface of the spring.

Ideally, the pump should be 12 / 24 volts to avoid the problems of the 100 volt 50Hz Japanese power supply - although a transformer could be used to change the mains voltage.

 

Thank you in advance,

 

Allen

[sharpener]

There is no intrinsic reason why it would not work but I would be nervous about putting yr spring water into the CH system directly without a detailed analysis of what else might be in the water, lots of iron if it is a chalybeate spring for example. At least use a fine inline strainer or Magnaclean.

 

25 ft would be a delivery head of only 1.7 bar (and of course the weight of the water in the descending leg of the circuit will help). Ordinary cast-iron bodied CH circulating pumps can achieve this and are designed to run non-stop for years, I would consider them first. Power consumption would be a lot less and lifetime a lot longer than a typical submersible or self-priming jet pump designed for intermittent use as dewatering or water supply pumps, they deliver much more than yr 4 l/min and usually draw many 100s of watts.

 

Small centrifugal pumps e.g. for shower boosting are available as low voltage but again are not designed for continuous use. I would have thought 100V CH pumps would readily be available in the Japanese market, unless you want to source the kit in the UK and bring it over in which case a small (auto-)transformer will not be expensive. IIRC some parts of Japan are (or were) 60Hz though that may not matter much.

 

HTH

 

 

Edited October 1 by sharpener

[AllenCherry]

Dear Sharpener,

 

Many thanks for your help!

I will be back in Japan over Christmas, and will carry out tests on the water,

Thanks also for your guidance on the pumps - again, I will do some research at various builders merchants to what is available.  It seems that 'central heating' is uncommon in Japanese homes - they use hot air or full air conditioning as a norm.

 

I'll let you know how I get on!

 

Best wishes,

 

Allen 

[sharpener]

7 hours ago, AllenCherry said:

research at various builders merchants

 

A pump specialist like anglia pumps will stock a wider range and perhaps be in a better position to give advice than a builders merchant methinks.

 

As you had spoken about "the heating system" I had supposed it was a pre-existing wet heating system as in the UK.