Hot water plumbing and controls

Forums › Home Workshop › Hot water plumbing and controls

Gordy7

406 posts

Ultimate Geek
+1 received by user: 28

Topic # 223528 4-Oct-2017 14:30

I am trying to understand my house hot water plumbing system and whether I have things set up correctly.

I thought I might have a problem with hot water loss as when we are away from home for some time, I shut off the hot water heating and this reduces my power usage from about $6 to $3 per day.

I have had a look up on my roof and there is no sign of water leaking out of the header pipe.

The tank is a Rheem low pressure cylinder dated 4/2001, but I don't understand all the valves, controls and settings.

I have labelled a photo.

1 Water drain... originally I thought this was a cold water feed

2 Drain valve... normally closed.

3 Pressure reducing valve.

4 Cold water feed shut off valve.

5 Cold water feed.

6 Anti-scald temperature regulator.

7 Hot water from top of cylinder.

8 Lower temperature water feed to sinks and shower, etc.

9 Low pressure cold water.

10 Cold water shut off valve to hot water cylinder.

11 Cold water into bottom of cylinder.

Any updates would be most welcome...

Gordy

1 | 2 | 3

3948 posts

Uber Geek
+1 received by user: 2009

Trusted

Subscriber

Reply # 1877266 4-Oct-2017 14:41

Looks to me like you've correctly labelled all the parts.

Gordy7

406 posts

Ultimate Geek
+1 received by user: 28

Reply # 1877267 4-Oct-2017 14:44

My first assumptions about how things worked, I managed to flush all the hot water out of the tank!

Gordy

RunningMan

4412 posts

Uber Geek
+1 received by user: 1245

Reply # 1877272 4-Oct-2017 14:50

6 = tempering valve.

Pinging @aredwood

Aredwood

1923 posts

Uber Geek
+1 received by user: 608

Subscriber

Reply # 1877378 4-Oct-2017 17:04

Yes number 6 is the tempering valve.

Do pipes 7 and 8 go completely cold if hot water has not been used for a few hours? Also there will be either an open vent pipe through your roof or a pressure relief valve on your cylinder. check that it is not discharging water.

If You have hot water pipes in a concrete slab, it is also common for them to leak. Have seen this so bad at times that the leaking hot water pipes were acting as an effective but expensive underfloor heating system.

andrewNZ

1701 posts

Uber Geek
+1 received by user: 867

Reply # 1877404 4-Oct-2017 18:26

One person supports this post

I don't think $3 a day for hot water is necessarily bad, depending on your household and usage patterns.

Location: Dunedin

Jase2985

6929 posts

Uber Geek
+1 received by user: 2203

Subscriber

Reply # 1877467 4-Oct-2017 20:39

we used 3h21m worth of hot water heating yesterday (2012 mains pressure cylinder with 3kw element), 2 adults having showers and a bath for the 2 kids + washing the dishes.

Gordy7

406 posts

Ultimate Geek
+1 received by user: 28

Reply # 1877487 4-Oct-2017 21:28

A few answers to questions raised.

Wooden floor.... and I can see hot and cold pipes running under floor along the length of the house. No sign of any other pressure valves.

The $6/day away from home with water heating on. The $3/day away from home with water heating off... Autumn to mid winter. East coast of North Island. The cylinder is in a cupboard. I have wondered if the cylinder insulation could be better.

There is a header pipe above the roof about 1.2 to 1.5m. Probably top of the header pipe about 3m above the top of the hot water cylinder.

There is no sign of leakage from the header pipe... no staining on the corrugated iron...

I will check the temperatures either side of the temper valve tomorrow... checks I did tonight by hand showed very little temperature difference... probably because of thermal conduction.. generally luke warm either side...

Gordy

Aredwood

1923 posts

Uber Geek
+1 received by user: 608

Subscriber

Reply # 1877547 5-Oct-2017 01:10

What is the usage in KW/Hr? As $ per day is pretty meaningless without knowing your per unit cost. And some power companies have different time based rates or roll the fixed fees into the $ per day figures. I take it that you are also waiting 2 days or so between switching on the cylinder and starting to take usage readings? To give plenty of time for things like cupboard temps to stabilise.

Does the property have a single meter for all power usage, or is there a separate hot water meter? And what kind of pricing structure is the property on? Uncontrolled, controlled hot water, night rate hot water, day / night for the whole property etc?

How are you switching off the hot water? Switch next to the cylinder or on the switchboard / meterboard? As if the hot water power usage is charged at a cheaper rate, someone might have taken a feed from the hot water circuit for something else to get the cheaper power. And switching off the hot water at the meterbox will be switching that load off as well.

If you have a F&P smartdrive washingmachine, some of them have a feature called controlled cold. Meaning they will take in a little bit of hot water, even when set to cold wash. Which is done to get a wash temp of 20deg or so - helps the powder to dissolve. You might be using hot water without realising it.

Try turning off valve 10 and then taking your usage readings (power still on). As I have seen faulty tempering valves allow water to circulate from the outlet back into the inlet again under thermosiphon action. You get way higher heat losses if this happens. If turning off valve 10 reduces the power usage, you either have a failed tempering valve. Or you are loosing hot water somewhere that you haven't found yet.

DarthKermit

3948 posts

Uber Geek
+1 received by user: 2009

Trusted

Subscriber

Reply # 1877549 5-Oct-2017 02:24

The thread author says the cylinder dates from 2001. I wonder if that's a replacement cylinder? (He can tell us if it's younger than the house.)

When a new cylinder is fitted, is there a regulation requiring a retro-fit of a tempering valve? (All that additional polybutylene plumbing looks to me to be a lot newer than the rest of the installation.)

Could any leaking water at valve 2 account for loss of hot water from the system?

Regarding Aredwood's point about faulty tempering valves: if the horizontal pipe near label 9 was warm, would that indicate a fault?

Gordy7

406 posts

Ultimate Geek
+1 received by user: 28

Reply # 1877660 5-Oct-2017 09:51

When we are away from home and with the water heating power switched turned on, the power used by hot water cylinder is 10.6kWhr/day ($3/0.2846c/kWhr). This info was obtained after being away from home for a week or more.

Power rates are water 28.46c/kWhr and all other power is rated at 37.82c/kWhr with Energy Online.

When we are away from home and the water heating power is on our total power usage is $6/day. When we are away from home and the water heating power is off our total power usage is about $3/day.

I am on a smart meter with separate metering for water. With all the limited info on my smart phone presenting usage as $/day. Maybe all too much info :-)

House appears to have been built in 2001 and is the same date as on the cylinder.

I have been turning off the water heating at the switch board (controlled) circuit breaker. I am pretty confident that all other power loads are going to other uncontrolled circuit breakers. I always find it annoying that sparkies are pretty slack on labelleing so I have identified all loads and associated circuit breakers.

I have checked all taps and had a quick look at the underfloor plumbing shows no signs of leaks.

I can see pipe 1 (drainage) dangling under the house, and no sign of leakage there. So valve 2 must be well and truly shut.

What is interesting is that the header pipe up through the roof is un-insulated. I am wondering if there is significant conduction loss and even some evaporative loss at the water interface in the header pipe. In a house I had down in the South Island, the header pipe was all insulated.

I am beginning to wonder if the losses are what we have to pay for having on-tap ready hot water and also a sign of the water heating and plumbing technology available around 2001.

I have also decided to try and get the water heating losses into perspective. I have created a list of all the other electrical things in my house that are running or on standby. Quite a long list and the subject of another posting!

Gordy

mclean

291 posts

Ultimate Geek
+1 received by user: 60

Subscriber

Reply # 1877678 5-Oct-2017 10:01

As Aredwood says, you need to pin down the energy consumption in kWhrs for both cases. That's easy if you have a separate meter for water heating, a lot harder if you don't.

Making an assumption about your tariff, $3.00 indicates a demand of maybe 600W over 24 hrs. That seems a bit high for the standing loss, but if the tariff assumption is wrong and the $3.00 is not accurate then you can't really say.

McLean

Gordy7

406 posts

Ultimate Geek
+1 received by user: 28

Reply # 1877697 5-Oct-2017 10:26

Not an assumption....

$3/0.2846 = 10.54kWhr usage per day

or 10.54/24 = 0.439kW losses

Gordy

Aredwood

1923 posts

Uber Geek
+1 received by user: 608

Subscriber

Reply # 1878209 5-Oct-2017 23:31

Gordy7:

Not an assumption....

$3/0.2846 = 10.54kWhr usage per day

or 10.54/24 = 0.439kW losses

What are the usage readings recorded by the hot water meter? As it is far more accurate to go to the source of the data rather than simply assume that the power companies billing system is guaranteed correct. And have you tested by turning off the switch next to the hot water cylinder? Both to prove that there are no other loads connected to the hot water circuit. And also to prove that the metering and billing systems are correct. As the hot water meter should then record Zero usage, and the bill should also say Zero hot water usage.

With these sorts of things you need to prove 100% every step of the chain. I will ask my parents how much their monthly KW/Hr power usage is. As they say that their bills are less than $100 per month. Which implies that their daily usage is around 11KW/Hr per day - So not much more than your hot water usage. Even though they are living in the house, using hot water and power for lights, cooking, appliances etc. And their house still has the original cylinder from the 80s, which is open vented. (above assumption of my parents usage is based on $100 per 31 day month, 25c per unit inc GST, 33c per day fixed fees)

If you can't take direct readings from your meters (surely not that hard to do when you are visiting the property?) Your monthly powerbills should at least have per month totals for each meter. And since you have a smart meter, your power company is probably doing at least daily meter reads. Or could be doing 1/2 hour meter reads. Ask them to provide this data to you. By law they must provide it if you ask for it.

And then there is verifying the metering setup is correctly wired - I was told by an electrical inspector who's job it was to randomly audit smart meter installs. He once found a 2 meter setup (house meter and hot water meter). Where the hot water load went through both meters - That house was getting billed double for their hot water power usage. And if there is an insulation fault on the pilot wire between the meter board and switchboard - You will also have extra power usage on the hot water meter. (can easily happen on an underground cable)

Your numbers say that you have heat loss equivalent to a 439w heater running 24/7. If that heat loss was solely from your hot water cylinder, your hot water cupboard would be getting really hot. And assuming that your cylinder has a 2KW element, that element would have to be switched on for 5.27 hours per 24 hour day. (close to a 1 in 4 ratio) So 1/2 hour meter data will be another way of checking. Even a 50W heater or other resistive load like a halogen lamp will easily get hot enough to set things on fire. So it shouldn't be hard to trace where 439W of heat is disappearing to.

Any electrician will (or should easily be able to) measure the current draw and voltage at the element terminals. To accurately calculate how many watts the element is rated at. And then run the element for say 15 or 30min. And check that the meter has recorded the correct amount of usage.

If you think that Im suspicious of your numbers - well I am. But remember:

Test - Don't guess.

Jase2985

6929 posts

Uber Geek
+1 received by user: 2203

Subscriber

Reply # 1878384 6-Oct-2017 11:02

yea something doesnt look right

Gordy7

406 posts

Ultimate Geek
+1 received by user: 28

Reply # 1880239 10-Oct-2017 10:01

Thanks for all your help.

I now have a better understanding of the controls and a bit more confidence that leaks are not causing heating losses.

The main trigger for the search for losses was the apparent $3/day. While this may not be accurate it indicates a problem.

Branz mentions standing losses of 2.5kWh/day (or about 33% loss) in one report and 3.56kWh/day in another. Way lower than my estimated 10kWh/day.

Energy Wise suggests using a cylinder insulation wrap around pre-2002 cylinders... Mine is dated 2001.

Also suggested is insulating the first 1 to 1.5m of the header pipe.

What I see now is that my cylinder outside is quite warm and very little insulation on the hot header pipe. The tempered water temperature at a hot tap is 47C. I would like to measure then cylinder temperature but not sure how to get a good result..

I recently switched from Energy Online (who provided smart phone monitoring) to Grey Power Electricity.

My plan is to get a more accurate measure of the energy loss. Either by manually reading the meter or seeing if Grey Power Electricity or Welles can provide the meter readings remotely or maybe fitting a camera to the meter box to capture scheduled readings.

The cylinder element is 3kW. I have made measurements at the switch board of 13.4A and 234v which is 3.135Kw. There may be a bit less power at the cylinder due to voltage drop.

Gordy

1 | 2 | 3