What is the most efficient method of heating large volumes of water?

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#1301808 11-May-2015 10:51

trig42:
blackjack17:

1400L = 14m3 and if you had a used tank and a fresh tank that two of them, they would take up a lot of space

(I'm a science teacher but not a physicist)

1400L = 1.4 m3 - 1 Cubic Meter = 1000 Litres = 1000 kg (assuming pure water 1ml = 1g).

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#1301828 11-May-2015 11:10

Solar, with a (very) large storage capacity.

bcraig

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#1301898 11-May-2015 12:32

trigg42: It is going to be expensive to heat, which is why you generally only see these places in thermal areas (Have you been to the Te Aroha hot pools? - they empty their tubs after every use, but the hot water comes out of the ground).

What are you going to use to filter the water to re-use it? After sitting in the pools at Te Aroha for just half an hour, the amount of oils and dead skin you see floating on the surface is pretty gross (hence why they empty them). Also, half an hour at Te Aroha is $18pp, which I consider well up there in price - their hot water will be a lot cheaper than yours - how much are you planning to charge? (http://www.tearohamineralspas.co.nz/index.php/prices)

We will charge more than the majority of thermal pools located around NZ but we will be focusing on uniqueness and that's all I can say at this stage.
We will use use a filters, ozone and chlorine to manage the water. So the water will be filtered for solids while in use and then drained, filtered and treated after every use.

raytaylor: Is the pool heat pump capable of putting out 38 degrees? You want to get the input to the gas califont as hot as possible before actually consuming gas. So if the desired temperature is between 30 and 40 degrees, you at least want to bring the input up to 30 degrees so gas can heat the rest. The heating you do with a heat pump is going to be cheaper than the heating with the gas....

This is the chart I was looking at with heater specs.
http://www.wep.co.nz/wep/member-images/302/file/HotWatereletricHeatPumpBrochure.pdf
Those units can maintain temperature up to 45 degrees. But I agree that maintaining 30 degrees would be best as this is probably the lowest temperature that a user may want. Then a secondary heater will make up the rest for higher temps.

I might try some small scale experiments with heat loss.

k1wi: Heat recovery from your waste water is going to be key to keeping your costs low. Both in terms of not flushing heat down the drain and in increasing the capacity of whatever system you use....

Agreed. I think with a combination of heat recovery and solar I could have a very economical system.

mclean: You probably need to think about how you're going to manage the pools. For example, do you want individual temperature control at each pool? Are you going to use a central filtration plant or one for each pool? Do you want to have the pools ready and up to temperature when customers arrive?....

The idea is to have maybe 3-4 predetermined temperature options for customers. The lowest option would probably be 30 degrees so the thinking is that there would be one big storage which holds all the water, maybe 10,000L at 30 degrees which has the main filtration and treatment system hooked into that. To account for walk in customers I would like a pool to be filled within 15 minutes. So the 30 degree water could be pumped to a bath through a secondary heater on each bath to instantly bring the temperature up to say 40 degrees if that's what the customer chose. The bath water would then be locally circulated with its own small basic filter and heater to maintain 40 degrees which isn't adjustable for the customer.

I think storing the water in the baths would lead to the most heat loss and running so many extra units wouldn't be the most efficient way. Storing all water in one large tank would ensure a tightly sealed, well insulated space and would make treatment simpler. When hotter temperatures are called for then sent back for storage then this water would assist in maintaining the 30 degrees in the storage tank, increasing efficiency. Maybe the storage tank could be kept at the most commonly used temperature that customers requested for example 38 degrees, so then less energy is drawn from the instant water heater on a bath fill. If anything under 38 degrees was required then it could be left to evaporate or cold could be added.

I haven't begun to look into the chemistry of water too much yet but if backwash or at least it's heat can be reused in an efficient way I will definitely want to look into that.

Does anyone have any knowledge on wood burner boilers or some sort of solid energy type boilers? I wonder how their efficiency compares. Would it be practical while having to refuel. What would emissions be like? This could possibly be an issue in retail type zoned areas.

blackjack17

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#1301909 11-May-2015 12:50

Might large vats of warm water be a possible pathogen issue eg Legionella bacteria

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bcraig

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#1301923 11-May-2015 13:04

blackjack17: Might large vats of warm water be a possible pathogen issue eg Legionella bacteria

The water will be constantly circulating and being treated in the storage tank. And dumped approximately once a week depending on the volume of service.

You could imagine it as one large spa bath that shares its water will small ones.

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#1301941 11-May-2015 13:34

bcraig:
blackjack17: Might large vats of warm water be a possible pathogen issue eg Legionella bacteria

The water will be constantly circulating and being treated in the storage tank. And dumped approximately once a week depending on the volume of service.

You could imagine it as one large spa bath that shares its water will small ones.

What will happen in a code yellow/brown?

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#1301962 11-May-2015 14:01

Doggy bags will be provided. Haha

I'm not sure on the chemistry of things completely yet but I imagine that yellow/brown will be nutilised by the ozone, chlorine and possibly further chemicals if that's what is required. But this will only be treated after the customers session and the bath is drained. So it's up to them if they want to bath in that or not. Solids will be filtered.

KShips

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#1301965 11-May-2015 14:12

Not sure if the feasibility but you might want to look at Heatworks to boost the temperature to a high accuracy http://myheatworks.com and/or maybe one per spa as well for a efficient way of maintaining temp?

If running storage at 30 degrees, you could use a bank of HeatWorks units (power requirements will be interesting) to dump water through boosting to precision temp settings (that is also controllable over wifi so easily setup to front desk)?

Will be interesting to see what solution you come up with.

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#1301989 11-May-2015 14:53

bcraig:

k1wi: Heat recovery from your waste water is going to be key to keeping your costs low. Both in terms of not flushing heat down the drain and in increasing the capacity of whatever system you use....

Agreed. I think with a combination of heat recovery and solar I could have a very economical system.

Heat recovery is great but I think that you need to work out the profile for your water heating requirements before deciding what else will be most economic. I would be seriously looking at heat pumps if lloking at solar because heat pumps are more useful on cloudy days and both will work more efficiently at lower output temperatures, 30-40C, than the usual 55C for hot water. But their effectiveness depends upon where you are in NZ and what time of the day and the year you need the heated water.

Insulation normally has a very good payback and in your case it will be a lot higher if you are moving and, maybe, storing large volumes of water. In NZ, you will almost always get an economic return in domestic systems using 15cm on everything including pipes. I read a US study about ten years ago (which I couldn't find today [but this link gives you some ideas about "superinsulating"]) where they found economic returns for some domestic hot water cylinders insulated up to, from memory, 45cm.

If you're going with solar water heating in a new build then consider building the collectors into a roof cavity behind low-emissivity glass rather than placing it on top of the roof. It looks better for a start and the reduction in heat losses will be significant particularly where the weather is wet or windy. It will also be easier to maintain the solar system undercover and the part of the roof where you would otherwise be hindered by the attached system. There will be an additional cost for a tray to catch any fluid release that would normally spill onto the roof.

Cnnsider a tracking solar system. This NIWA two page document is one of several useful resources on their website including the Solarview calculator [which calculates solar values by month and hour of day for any address in NZ. It is free to register as a public user.] You'll see that you can get about a third more energy by having a solar system tracking the sun instead of at optimal tilt which gives 50% more than laying it flat. With a bigger spend the tracking cost becomes a smaller proportion so it is more likely to be an option for you.

You mention filtering solids when recycling water but you don't mention trapping all the grease/oils/fats. That will also be an issue using heat exchangers, i.e. the fats congeal and foul the transfer surfaces to reduce efficiency. Don't forget to factor in the commercial costs for water supply and include the relevant benefit for recycling.

[Edited to add note on Solarview and link for "superinsulating"]

mclean

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#1302037 11-May-2015 15:48

bcraig: .....I think storing the water in the baths would lead to the most heat loss and running so many extra units wouldn't be the most efficient way. Storing all water in one large tank would ensure a tightly sealed, well insulated space and would make treatment simpler. When hotter temperatures are called for then sent back for storage then this water would assist in maintaining the 30 degrees in the storage tank, increasing efficiency. Maybe the storage tank could be kept at the most commonly used temperature that customers requested for example 38 degrees, so then less energy is drawn from the instant water heater on a bath fill. If anything under 38 degrees was required then it could be left to evaporate or cold could be added.

1500 litres x 10 degC in 15 minutes is 70 kW. That will heat one fill at a time. If it's a commercial operation then two heaters at say 50kW might be better. If you're thinking off-the-shelf heat pumps then remember to select the units for spa pool duty, not normal pool duty, ie 38 degC leaving water temperature (probably about 50 degC condensing temperature). You will still need a small heater at each pool to maintain the temperature while it's in use - I'm guessing 2-3 kW.

There's going to be a lot of money/options here. If you're not one yourself then I suggest to engage a good mechanical engineer.

bcraig

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#1302042 11-May-2015 15:56

KShips: Not sure if the feasibility but you might want to look at Heatworks to boost the temperature to a high accuracy http://myheatworks.com and/or maybe one per spa as well for a efficient way of maintaining temp?

If running storage at 30 degrees, you could use a bank of HeatWorks units (power requirements will be interesting) to dump water through boosting to precision temp settings (that is also controllable over wifi so easily setup to front desk)?

Will be interesting to see what solution you come up with.

Automation would be amazing. I would love to be able to control the entire system from the desk.
I will be reading up on HeatWorks. Thanks for the link.
Please send links or names if anyone else knows of other automated products to do with heat, pump, valve control.

Hammerer: Heat recovery is great but I think that you need to work out the profile for your water heating requirements before deciding what else will be most economic. I would be seriously looking at heat pumps if lloking at solar because heat pumps are more useful on cloudy days and both will work more efficiently at lower output temperatures, 30-40C, than the usual 55C for hot water. But their effectiveness depends upon where you are in NZ and what time of the day and the year you need the heated water.

Insulation normally has a very good payback and in your case it will be a lot higher if you are moving and, maybe, storing large volumes of water. In NZ, you will almost always get an economic return in domestic systems using 15cm on everything including pipes. I read a US study about ten years ago (which I couldn't find today [but this link gives you some ideas about "superinsulating"]) where they found economic returns for some domestic hot water cylinders insulated up to, from memory, 45cm.

If you're going with solar water heating in a new build then consider building the collectors into a roof cavity behind low-emissivity glass rather than placing it on top of the roof. It looks better for a start and the reduction in heat losses will be significant particularly where the weather is wet or windy. It will also be easier to maintain the solar system undercover and the part of the roof where you would otherwise be hindered by the attached system. There will be an additional cost for a tray to catch any fluid release that would normally spill onto the roof.

Cnnsider a tracking solar system. This NIWA two page document is one of several useful resources on their website including the Solarview calculator [which calculates solar values by month and hour of day for any address in NZ. It is free to register as a public user.] You'll see that you can get about a third more energy by having a solar system tracking the sun instead of at optimal tilt which gives 50% more than laying it flat. With a bigger spend the tracking cost becomes a smaller proportion so it is more likely to be an option for you.

You mention filtering solids when recycling water but you don't mention trapping all the grease/oils/fats. That will also be an issue using heat exchangers, i.e. the fats congeal and foul the transfer surfaces to reduce efficiency. Don't forget to factor in the commercial costs for water supply and include the relevant benefit for recycling.

[Edited to add note on Solarview and link for "superinsulating"]

I am becoming very keen on heat pump heaters for the main body of water.
With solar would I use solar water piping or panels to power the heat pumps? Is there an energy advantage between the two? I imagine that the setup cost for panels would be much greater.
I haven't researched the water treatment too much yet and how I plan to remove contaminants but I will do.

Regarding insulating pipework I would like to be able to easily access any section of the piping for maintenance so I could possibly build insulated boxing around grouped pipe runs with hatch access.

I have some reading to do tonight, thanks for your information and references.

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#1302216 11-May-2015 19:39

The price of electric solar panels has come down to the point where no solar installs heat the water directly anymore. Solar EV / tube systems are less efficient than a electric PV array and heat pump system.

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#1302243 11-May-2015 20:11

For a system delivering hot tap hotness then that is certainly true, but there is still a long way to go before heatpump and PV can compete for pool heating with the cheaper solar water panels used for that.

Richard rich.ms

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#1302247 11-May-2015 20:16

Yes thats true, but remember a pool only needs to be heated to 26 degrees which anyone can do with a long enough length of alkathene.
But heating to 38 degrees is a bit different.

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#1302248 11-May-2015 20:20

Nuclear Fission?

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