Browse Forums Eco Living 1 Sep 09, 2016 8:31 pm On tank water only and we're having troubles with our Rinnai 20 instant HWS. The Rinnai is fed by the pump via a 60L 'Pressure Wave' pressure tank. It seems as the pressure tank delivers its 20 or so litres before the pump kicks in, the Rinnai is sensing the slow drop in pressure and I can hear its booster fan start and stop and we get moments of hot than warm, than the correct temp again. And when the pump does finally kick in after 4-5 mins the Rinnai seems to "drop out" suddenly then "adjust" to the new pressure. The Rinnai has a temp control panel in the bathroom set at 44C.
Our plumber has checked the regulator and gas pressure at the HWS while running and it's reading around 2.8kpa so apparently fine for the Rinnai. He recommends to delete the pressure pump or get a smaller 20L tank so when showering it has little effect but we still get 8L or so without the pump coming on when brushing our teeth or flushing the toilet. We went with the 60L pressure tank to minimise pump starts but the varying pressure seems to be upsetting the Rinnai. Re: Rinnai HWS & Pressure Tank 2Sep 09, 2016 8:44 pm This is the pump & 60L pressure tank we have. http://www.ebay.com.au/itm/Small-House- ... 1799853972 http://www.dabpumpsaustralia.com.au/Sid ... Tanks.aspx Re: Rinnai HWS & Pressure Tank 3Sep 10, 2016 2:18 am The pressure tank is a good tank and size, I have the same one. They come from the factory set to 30 psi pressure. It has about 18 litres draw down at 30 psi but less as the pressure is raised. The pump appears to be the TLE 1A. This is a small pump with a 35metre head. 1 metre head = 1.42 psi and so the 35 metre head is nearly 50 psi. The pump's specs indicate that it has an adjustable automatic pressure controller which is very unusual but I don't know what degree of pressure adjustment it gives. The pump's cut in - cut out pressure settings when using a pressure tank must cut out before the pump's maximum rated setting and cut back in before the tank empties. Lets assume that the tank's pressure is unchanged at 30 psi. In this scenario, the pump's controller would be set to cut in at 32-33 psi and cut out at perhaps 45 psi. This would give a small pressure variance that would minimise pressure fluctuation but such a small variance is unusual as it also increases cycling. An instantaneous gas hws requires good pressure and you need to check the pressure settings because if the tank is delivering 20 litres as you say, then the tank's pressure would be less than 30 psi. You have little leeway with such a small pump and if you were able to raise the cut in - cut out pressure to 35 - 45 psi, you could try that and see how it goes but the pump would be cycling more often which isn't good for a pump. Failing that, you would need to disconnect the tank and readjust the controller's pressure setting to suit the pump. The plumber's recommendation to get a smaller pressure tank is a bad one. The size of the tank is not the issue, it is the cut in pressure setting and the pressure variance. A smaller tank with a faster draw down will also cause the pump to cycle more often. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Rinnai HWS & Pressure Tank 4Sep 10, 2016 9:13 am Thanks for the reply. The pressure tank was originally installed to reduce pump startups so less wear, and supposedly less power. But, I have since tested the pump with my power meter and found there is no start up power spike. Always a constant load. Maybe the hydro control somehow helps with this. The power meter shows 1-2w on standby then about 390w when starting or running. The meter does not show higher than 400w was detected. So that kinda kills the power saving benefit with a pressure tank. In regard to pump run times, the pump does seem to "run on" when recharging the pressure tank. Now realise why from what you've said about cut off pressure. The pump is trying to reach its cut off pressure but the pressure tank delays this while pressure builds slowly in the bladder. Imagine this would stretch the bladder overtime and make the problem worse. Actually, have noticed it is taking longer than when first installed. I've tried adjusting the pump but still obviously doesn't bring the cut off low enough to stop the "run on". If we change to a 20L tank, yes the pump would cycle more often but actual runtime may reduce overall. If I take the pressure tank out of line, the pump starts when I open a tap and stops within 10secs of closing the tap. As you say the constant stop/start is not good for the pump but at least with a 20L the short tap openings are covered. And the pump maybe won't run on as much as it does with the 60L. The 20L may solve the shower issues as the pump would start (and stay on) within a minute as the shower head is 9L/min. So the pressure would remain constant throughout the shower as the pump is always on. The larger pressure tanks don't seem to be commonly used. Most neighbours just use a Grundfos type pump with very small pressure tank (8L) sitting on top. I've asked around and noone has our issue with their instantaneous gas HWS. This is probably the reason our plumber suggests a smaller tank. A good shower is the priority over pump wear. Especially when I'm using an almost sacrificial pump at its price. Very cheap to replace and just about time to buy a spare anyway. The ebay pump we use is the equivalent of a DAB pump worth $600 retail. DAB often sell it for half that though. Please feel free to shoot holes in my logic. I have a habit of missing the obvious. Re: Rinnai HWS & Pressure Tank 5Sep 10, 2016 11:26 am The run on is almost certainly caused by the pump trying to reach its normal cut off pressure whereas it should be adjusted to the tank's desired cut out pressure. This uses a lot more power and completely negates any benefit of having a pressure tank. The Grundfos pumps that you mention are most likely variable speed drive (VSD) pumps, VSD pumps have a soft start and a small pressure tank that provides high pressure water immediately on start up while the pump spools up to match the demand. VSD pumps are ideal for off water grid use because they are very energy efficient and provide constant pressure at the required flow rate but they are expensive (but well worthwhile IMHO). The energy needed to run a centrifugal pump is proportional to the cube of the speed. This means that 75% speed requires 42% full power and 50% speed requires 12.5% full power. Most house fixtures like showers, toilets and washing machines are low flow. Instantaneous gas HWS are very sensitive to low flow rates. I hope that the gas line is the correct size. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Rinnai HWS & Pressure Tank 6Sep 10, 2016 11:49 am Yes there's not enough adjustment in the pump to bring it down to suit the pressure tank. The Rinnai are a lot better now with low flow. I can turn the shower down to around 4-5L/min without issue. I either take the pressure tank out altogether or try the 20L for $155. I think the bladder has expanded anyway on the 60L from the run on issue. Taking 3-4mins now. A Grundfos would be better but at $1400 odd.... And it would still be constant stop/start though. Surely not good long term. Q. Do you get the run on issue with your 60L, & what pump do have have? Re: Rinnai HWS & Pressure Tank 7Sep 10, 2016 12:02 pm firebird In regard to pump run times, the pump does seem to "run on" when recharging the pressure tank. Now realise why from what you've said about cut off pressure. The pump is trying to reach its cut off pressure but the pressure tank delays this while pressure builds slowly in the bladder. The tank will be 'full' (but mostly 70-75% air) at the pressure tank's desired cut off pressure but the pump is still trying to reach its maximum pressure cut out and this is extremely inefficient. The best way of thinking about it is to realise that the more head there is to pump against (more pressure in the tank in this instance), the slower the flow will be because the pump is effectively compressing air. It is a bad situation and also bad for the pump to have run on at very low efficiency levels. I don't have run on with my Pressure Wave tank. I have a Davey pump with an 8 litre pressure tank and the plumber who supplied and fitted it 17 years ago told me it would supply 8 litres of water to the toilet. I was doing marine design work at the time and knew nothing about rainwater harvesting and didn't know that most plumbers didn't know either. The pump has an electronic control that can't be adjusted and the 8 litre tank was set at 20 psi, meaning that the cut in pressure would be about 22-23 psi. All I had to do was reduce the Pressure Wave tank to 20 psi and connect it inline. You MUST do this when the tank is drained of water. Note that I am on mains water. firebird A Grundfos would be better but at $1400 odd.... And it would still be constant stop/start though. Surely not good long term. No it won't, it will adjust its speed and it has a soft start anyway. If you used the larger pressure tank in line with the small Grundfos pressure tank, it would have to have its pressure increased to match the smaller unit but there really is little need for it. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Rinnai HWS & Pressure Tank 8Sep 10, 2016 12:40 pm firebird I think the bladder has expanded anyway on the 60L from the run on issue. Taking 3-4mins now. The pressure tank will be ok, you could put 100 psi in it if you wanted. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Rinnai HWS & Pressure Tank 9Sep 10, 2016 1:08 pm I meant the Grundfos (without a larger pressure tank inline) would come on and off every time a tap is opened. Well, not everytime if it has its own 8L pressure tank onboard. Still, it will only deliver a few litres before starting. Would only cover a quick hand wash or quick glass rinse etc. Would start everytime for the toilet or when any tap is on for about 30 secs or so. Still a lot of stop/starts everyday. Maybe the soft start minimises wear. One neighbour's Grundfos is 9yrs old now with an 8L tank onboard. And it's not covered (under an eave) and subject to the weather a bit. Re: Rinnai HWS & Pressure Tank 10Sep 10, 2016 1:31 pm If I pump the pessure tank up to say 52psi (have to experiment) to satisfy the pump it'll then only deliver maybe 5L before the pump kicks in. But yes, that might be the solution. It would solve the run on issue and still reduce pump starts for the quick rinses etc. It might also fix the shower issue as well, as the pump would start (depending on the pressure tank's charge level) after a maximum of say 30secs amd stay running at stable pressure for the whole shower. Hmmm. .. will give it a go and report back. Didn't even occur to me to up the pressure tank's psi. Thanks for thinking out of the box on that one. Re: Rinnai HWS & Pressure Tank 11Sep 10, 2016 6:43 pm firebird If I pump the pessure tank up to say 52psi (have to experiment) to satisfy the pump it'll then only deliver maybe 5L before the pump kicks in. But yes, that might be the solution. It would solve the run on issue and still reduce pump starts for the quick rinses etc. If the pump is the TLE-1A, it has a 35 metre head which is just under 50 psi or 343 kPa but you need to know what the pressure controller's pressure settings are as should have the plumber when he installed the pressure tank. The pump's handbook should state these. Raising the pressure tank's pressure to 52 psi won't prevent run on because the pump will run until it reaches the pressure controller's cut out setting plus the pressure tank would always have 53 psi in it! The pump head is the maximum pressure that the pump will run at (depending on the pressure controller's setting) and running a pump with a lot of head resistance will substantially slow down the flow and stress the pump. The 45psi cut out figure I used in an earlier post was not a recommendation for your pump, it was merely an example. As a further example, my Davey pump also has a maximum total head of 35 metres, the same as the TLE-1A. The Davey pump came from the factory with a small 8 litre pressure tank fitted and so the pressure controller was factory adjusted for the pump to work with the pressure tank. For my pump, the cut in and cut out pressure settings are 140 kPa and 280 kPa. I would not consider using this pump and pressure tank with a shower or an instantaneous gas HWS because the pressure is too low, the pressure variation is too great and there would be too much cycling. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Rinnai HWS & Pressure Tank 12Sep 10, 2016 9:42 pm Ok, the penny has dropped. The controller is only adjustable for the cut-in. 1.5 - 3.5 bar. The cut-out is fixed at 8 bar (around 116psi), so we're back to square one. Now I see why the run on happens. The pump is trying to reach 116psi to cut out. Correct? If that's the case it's a wonder it cuts out at all. The guage on the controller quivers around the 4 bar mark for 3-4 mins then finally cuts out. I need a controller with an adjustable cut-out, if there is such a thing. Re: Rinnai HWS & Pressure Tank 14Sep 10, 2016 9:57 pm firebird The pump is trying to reach 116psi to cut out. Correct? The pump will only push to a 35 metre head. 1 metre = 1.42 psi or 9.81 kPa. It should cut out before that. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Rinnai HWS & Pressure Tank 15Sep 11, 2016 8:44 am So basically a pump with one of these type fixed controllers will never work with a pressure tank. Too much run on. What must others use with a pressure tank? There's got to be a correct way to do this. I can't be the only person with the problem. The plumber seems to just shrug his shoulders. He says he rarely sees pressure tanks used. Our original plumber has moved. Re: Rinnai HWS & Pressure Tank 16Sep 11, 2016 10:17 am firebird So basically a pump with one of these type fixed controllers will never work with a pressure tank. Too much run on. What must others use with a pressure tank? There's got to be a correct way to do this. I can't be the only person with the problem. The plumber seems to just shrug his shoulders. He says he rarely sees pressure tanks used. Our original plumber has moved. A pump that comes with an electronic pressure controller operates with factory pressure settings that suits that particular pump. Electronic pressure controllers also have run dry protection because they sense when there is no available water. If the same pump and electronic pressure controller comes from the factory with a pressure tank, the tank's pressure will be set to 'X' and the pressure controller's cut in - cut out settings will be set at the factory to work with the tank's pressure. These settings are different to the standard settings and they also vary between different pumps and tank pressures. Most electronic pressure controllers are generic and interchangeable between different pumps. Electronic pressure controllers to suit pressure tanks are also available, for example, if the one on my pump failed, I can easily buy another with the settings I need. You can fit a manual pressure controller like the common square D pressure switch and these are adjustable. Their standard pressure ranges are 20/40, 30/50 and 40/60. Manual pressure controllers do not have run dry protection and their use with small tanks needs close monitoring which is not often practical. Unlike electronic pressure controls, manual pressure switches are virtually bullet proof. They have also being around for years and are widely available. https://www.youtube.com/watch?v=5WNbxu9ufPs It is best to have high settings to decrease pressure variations when a pump with a pressure tank is used for showers etc. There is a fair difference between a pressure variance of 20/40 and 40/60. While outwardly it would seem that they both have a difference of 20 psi which they do, the 40/60 is higher up the totem pole. Higher pressures require larger pumps, the reason that people look at pressure tanks with large pumps. When comparing the price of a large pump and a decent size pressure tank, VSD pumps that offer constant pressure, energy savings and a long life become very appealing. For your situation, you either need to disconnect the pressure tank or else change the pressure switch. EDIT: The electronic pressure controller in the link below is fully adjustable. http://www.theirrigationshop.com.au/shopping/proddetail.asp?prod=781 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Rinnai HWS & Pressure Tank 17Sep 11, 2016 12:57 pm Thanks for the info and your time with this. A new electronic pressure controller seems the easiest solution, if I can find something suitable. The D switch looks a bit tricky for me. The pressure tank is now set at 30 psi. The current pressure controller has an adjustable cut-in range of 22-50 psi (1.5 to 3.5 bar), & a cut-out at around 87 psi (6 bar). I imagine I'd need a new controller with a cut-out around 46 to 48 psi, or 3.2 to 3.3 bar. The pump is about 50 psi as you say. I can only find controllers with an adjustable cut-in, and most have a very high fixed cut-out. Typically 6 to 10 bar. I'll have to ring around the plumbing shops. I'd like to keep the pressure tank as the pump stopping and starting 100 times a day is not desirable. Re: Rinnai HWS & Pressure Tank 18Sep 12, 2016 12:32 am As a matter of interest, I have just found my pump's installation instructions...all such paperwork goes in the one cupboard! The plumber told me that the pressure tank had to be set at 20 psi but I have always had it a little lower than this because of early gremlins. The cut in - cut out settings are 140 - 280 kPa and so I decided to look for the instructions after I realised that 140 kPa is 20.3 psi. It turns out that the tank's factory pressure setting is 19psi. Still, 19 psi with a 20.3 psi cut in is a bit fine for my liking. I think that your intention to have a 46 to 48 psi cut out will be damaging to the pump and waste energy. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Rinnai HWS & Pressure Tank 20Sep 12, 2016 12:54 pm firebird Oh, so if the pressure tank is 30 psi are you saying I only need a cut-out a few psi above that? I am somewhat hesitant to answer your question in this instance because a lot of people read these threads and their pumps and situations will be different and I would not want someone taking on board a recommendation given to you and using it for a different situation. The cut in pressure is always above the tank's pressure, if you persevere with the pressure tank, maybe initially try 3-4 psi above the tank's pressure. Also be aware that the pressure tank's pressure must be checked at least annually but preferably more frequently than annually. The tank must be drained before the pressure is checked and adjusted. Pump types vary as do the applications such as some properties having underground tanks or submersible pumps etc. I mentioned my Davey pump earlier because it also has a 35 meter head and we were discussing different pressure switch settings when pumps were fitted at the factory with a pressure tank but it is a centrifugal pump whereas yours is a turbine pump. Turbine pumps are known by various names and you can read about them below. The operating differences between centrifugal and turbine pumps are also explained. You Tube is also a good source of information. http://www.rothpump.com/regenerative-tu ... -head.html The statement below is taken from the link above. Regenerative turbine pumps should not be operated against a closed discharge, unless a pressure relief valve is used. Install a pressure gauge on the pump's discharge, observe the manufacturer's pressure limits and you'll increase the pump's life. A centrifugal pump usually has the cut in pressure 2 psi above the pressure tank's pressure but this also depends on the tank's elevation if applicable whereas some other types of pumps might require 5 psi. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. First time building 2 storey home, is under construction (in Framing stage) in NSW. I have 3 toilets and need bidet spray in… 0 16860 Thanks for letting us know. The programmer will have a look at this later today. 2 6692 |