Water Pressure

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#754531 1-Feb-2013 19:51

There are 2 systems:
Mains (high) pressure and Low pressure.

With Low in particular, you must pair this with the correct mixers (shower, kitchen) otherwise pressure with hot is stuffed up.

Low pressure systems do not put out as much water as high and all you can do in that situation is change the whole thing to high.
Or live with it, it's not that bad. Think of your Watercare bill if you go to high.

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#754541 1-Feb-2013 20:31

networkn:
Regs:
networkn:

He said the taps outside will be supplied by the inside water supply which also sounded weird.

i expect that means that the outside taps are split off *after* any pressure reducing valve that has been installed. I split my water feed to the outside taps via a second pressure valve - not via the one that feeds the inside taps. Turning on an outside tap doesnt impact the inside water pressure at all. All the pipes to my outside taps use 25mm blueline pipe all the way to the fitting also (but the fittings are not 25mm throat so that limit their throughput)

I presume you did that during the build or during a renovation? I think to do that now would be a major undertaking at our place.

nah, the plumber hooked everything up past the valve. A couple hours under the house with some blue line pipes and fittings sorted that out - it wasn't buried 😃

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#803870 22-Apr-2013 19:17

Man it's like pulling teeth trying to get plumbers interested in this problem.

If I buy a pump which I presume would be fitting in the bathroom I want to boost the pressure, will it matter if my rinnai gas thingy on the wall outside is rated at 15L per minute?

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#803901 22-Apr-2013 20:15

I'm going to guess that if you're rating to heat 15L/minute and you put 30L/minute through it won't be all that warm.

kiwirock

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#803909 22-Apr-2013 20:35

You'd have to calculate and use a suitable low or high pressure suited shower rose.

If flow was really a problem from having too much pressure, you'd use a high pressure - low flow shower head. The jet sizes would be smaller than a high flow low pressure head, so it helps maintain higher pressure but with less water delivered.

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#803920 22-Apr-2013 20:56

The Rheem system we have is 15L/m but when I went to the site it recommended 27L/m system but I doubt it's the limiting factor correct? It's not like the hot water heater is stopping more than 15L/m ?

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#803930 22-Apr-2013 20:57

kiwirock: You'd have to calculate and use a suitable low or high pressure suited shower rose.

If flow was really a problem from having too much pressure, you'd use a high pressure - low flow shower head. The jet sizes would be smaller than a high flow low pressure head, so it helps maintain higher pressure but with less water delivered.

How do I calculate? Fill a bucket from the bathroom and work out Litres per minute?

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#803941 22-Apr-2013 21:22

networkn:
How do I calculate? Fill a bucket from the bathroom and work out Litres per minute?

That's pretty well what I did when sorting out our shower. Flow it from the shower though.

I used a plastic container about 2 litres in size and held it under the shower head and timed the flow with s stop watch until the container was nearly full. I weighed the container to calculate the amount of water, 1 kg = 1 litre. I did this three or four times to get an average. Don't forget to subtract the weight of the container.

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kiwirock

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#803945 22-Apr-2013 21:27

networkn: The Rheem system we have is 15L/m but when I went to the site it recommended 27L/m system but I doubt it's the limiting factor correct? It's not like the hot water heater is stopping more than 15L/m ?

I could only speculate on that. The smaller unit may have a smaller area for the water to pass through the heat exchanger, effectively limiting flow more for setup that requires a higher demand. It may only be the difference in heat output from the gas burner, or it could be bigger in all aspects etc...

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#803972 22-Apr-2013 22:16

Technofreak:
networkn:
How do I calculate? Fill a bucket from the bathroom and work out Litres per minute?

That's pretty well what I did when sorting out our shower. Flow it from the shower though.

I used a plastic container about 2 litres in size and held it under the shower head and timed the flow with s stop watch until the container was nearly full. I weighed the container to calculate the amount of water, 1 kg = 1 litre. I did this three or four times to get an average. Don't forget to subtract the weight of the container.

To get enough data for a serious analysis you will need to do that from the bathroom tap, from the shower head, then from the shower with the head removed.

After that minimum - then consider taps in other locations in case serious differences are revealed.

kiwirock

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#803982 22-Apr-2013 22:36

Yeah that would be right.

If you measure the water already coming out of your shower, that's not going to necessarily tell you what is deliverable before the rose and even before the mixer since any input mixer valves adjust flow and the rose may not be suitable for what you want already. You could check if there are bath taps in that room how fast a bucket fills from both taps open, compared to how fast it's filling in the shower. If they fill similar, and you don't have a low flow rose, a low flow rose would help increase pressure but at cost of flow. To know if they fill similar, you'd need to know the pressure that would be lost in height between bath taps and shower rose, to figure out what the max output on the shower would be with no restriction by the head or mixer.

Thinking more about booster pumps: If you put a hot water booster pump in but only on the hot side upstairs, the hot water delivered at the rose will be hotter at your favourite setting. So turning the hot down by swaying to the cold on the mixer may reduce the pressure gained on the hot side? Also reducing pressure to the cold side since it's from the same mains supply providing the regulator keeps up. So you'd probably need to boost the whole supply to the gas heater as well as to the cold side of the shower mixer earlier on in the plumbing rather than somewhere upstairs on the hot side only.

I think hot water booster pumps are used more where there is a low pressure cylinder setup to boost the hot supply and pressure to the mixer. Otherwise you'll need to boost the whole system if it's all mains, similar to boosting the whole system in a rain water tank feed system. That's where a pro plumber will know exactly what you need, and ask them for a guarantee on their estimated output pressure/flow increase and whether a new rose or mixer adjustment would be needed as well.

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#805216 24-Apr-2013 23:03

networkn: The Rheem system we have is 15L/m but when I went to the site it recommended 27L/m system but I doubt it's the limiting factor correct? It's not like the hot water heater is stopping more than 15L/m ?

Actually it is highly likely to be the water heater that is limiting things. That 16L per min is based on a 25deg temp rise. (hot water temp minus incoming cold water temp) If a larger temp rise is required the heater can only provide a lower flow. And if you try to draw more flow than what the Rinnai can provide it will start restricting the flow to maintain the set temperature.

The other issue is that the Rinnais have quite a large pressure drop. (150 kpa approx). This combined with your already lowish pressure and undersized water heater will be the cause of your problems.

The beast cause of action to fix? This depends on whether you want a "Rolls Royce" hot water system. A system where the shower will work but there will still be big temp or pressure changes when other taps are used. or something in between.

To get a better idea of wether a pump is required a "pressure drop" test needs to be done. In other words the amount of pressure being provided by the main at different flow rates needs to be checked. This will reveal if the problem is inside the house somewhere. If a bigger water meter or pipe from the meter to your house is required. A pump is required. Or the most extreme case of all. The water from the street is used solely to fill a water tank and a pump is connected to the tank to supply the house.

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#805241 24-Apr-2013 23:22

Aredwood:
networkn: The Rheem system we have is 15L/m but when I went to the site it recommended 27L/m system but I doubt it's the limiting factor correct? It's not like the hot water heater is stopping more than 15L/m ?

Actually it is highly likely to be the water heater that is limiting things. That 16L per min is based on a 25deg temp rise. (hot water temp minus incoming cold water temp) If a larger temp rise is required the heater can only provide a lower flow. And if you try to draw more flow than what the Rinnai can provide it will start restricting the flow to maintain the set temperature.

The other issue is that the Rinnais have quite a large pressure drop. (150 kpa approx). This combined with your already lowish pressure and undersized water heater will be the cause of your problems.

The beast cause of action to fix? This depends on whether you want a "Rolls Royce" hot water system. A system where the shower will work but there will still be big temp or pressure changes when other taps are used. or something in between.

To get a better idea of wether a pump is required a "pressure drop" test needs to be done. In other words the amount of pressure being provided by the main at different flow rates needs to be checked. This will reveal if the problem is inside the house somewhere. If a bigger water meter or pipe from the meter to your house is required. A pump is required. Or the most extreme case of all. The water from the street is used solely to fill a water tank and a pump is connected to the tank to supply the house.

Thanks. I actually called and spoke to Rheem today and they told me a similar thing. The tech was HORRIFIED (He actually made me go and recheck whilst I was on the phone) that a 5 Bedroom 3 Bathroom home would ever have such a small system, said 27L/M would be the minimum recommended one. If I am loosing 150KPI then that I am sure would certainly help if I could get it back. No room for a water tank I don't think.

He wanted me to turn on all three showers and time how long it takes to fill a bucket done three times, but I couldn't really follow his logic, as it's not satisfactory with only 1 shower going. He was a little surprised that there doesn't seem (without specific testing) to be a big difference between completely cold water pressure vs hot pressure, though I need to test to be sure.

I'm happy within reason to pay to fix this problem, we have a lot of showers in our house and I use it to start my day.

the developer assures me that he used bigger than normal pipes which the watercare person confirmed and was happy about, but I don't know about inside the house.

When you say

To get a better idea of wether a pump is required a "pressure drop" test needs to be done. In other words the amount of pressure being provided by the main at different flow rates needs to be checked.

What do recommend specifically?

I think the 27L/M was about $3K which seemed an expensive solution, but I gather that with a 15L/M system it's unlikely a pump at the shower end would help much.

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#805409 25-Apr-2013 12:22

networkn: I think the 27L/M was about $3K which seemed an expensive solution, but I gather that with a 15L/M system it's unlikely a pump at the shower end would help much.

The averagish NZ shower head provides about 9 - 12 L/M at mains pressure. Boosting the pressure will probably not increase flow that much therefore not a problem for the supply

It would still be interesting to know what flow you are getting at present from the different points. A stopwatch and a paint pail will tell you what you need to know in a minute from the shower end.

As an aside, it might also be interesting to buy or borrow a different shower head and/or try a low pressure head. If an LP head solves the problem enough it could potentially be a $30 solution for a while.

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#805417 25-Apr-2013 12:34

It might be interesting to talk to this guy and see what his perspective is. He's being going for a while and has probably experience of good or bad results with this kind of fix in different situations:

http://www.trademe.co.nz/building-renovation/bathroom/showers/shower-heads-mixers/auction-584729215.htm

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