ASHP - LG Therma V Water flow issues - Plumber vs Installer

[Woze]

Hello,

 

Firstly, I wanted to say thank you to anyone being able to help with this.

 

We undertook a complete retrofit of a Victorian Terraced house. Since it was in very bad condition all the plumbing and heating had to be replaced.

 

We took the opportunity to install a LG Therma V heatpump. We were very relieved to see that the house is heating up well through the UFH BUT very early on we noticed that it takes 2 mins for warm water to arrive in the shower one floor up from the GF plantroom. The upper floor closely to 3mins. We wouldn't mind that if we are talking about an old house - but this is essentially all new!

 

We discovered meanwhile that 1.No return pipe had been installed and 2.All the pipes all have the standard diameter of 22mm instead of 28mm. We are not experts but are currently trying to figure out what the issue would be.

The plumber is saying a return pipe to the existing water cylinder is not standard and that's why he didn't install it and the heat pump contractor says that he was only there to install the heat pump, nothing else.

 

Any advice or experience in that matter would be much appreciated.

 

Thanks in advance!

[JohnMo]

Hot water return circuit is NOT a standard install, you would have needed to ask for that prior to work starting.

 

Pipe sizes depend on pressure drop.  Why do you think you need 28mm.  If it's 28mm on a domestic hot water feed to the taps, then you may get fed up waiting for the hot water to arrive, it would take an age. My feeds to bathrooms are 15mm, the furthest away can take a couple of mins for the shower to come hot.  Pipe length and volume all have an effect on hot water delivery time.

[ProDave]

Where is the hot water tank in relation to the bathrooms?

 

There is a trend for heat pump installers to fit the hot water cylinder right close to where the heat pump pipes enter the house, in many cases a very long way from the point of use.

 

any plumber worth his salt would be advising put the HW cylinder as central as possible to the points of use to minimise the length of pipe and then use thinner pipe like no more than 15mm to minimise the volume of water that must pass through before the hot water arrives at the tap.

[Woze]

3 hours ago, JohnMo said:

Hot water return circuit is NOT a standard install, you would have needed to ask for that prior to work starting.

 

Pipe sizes depend on pressure drop.  Why do you think you need 28mm.  If it's 28mm on a domestic hot water feed to the taps, then you may get fed up waiting for the hot water to arrive, it would take an age. My feeds to bathrooms are 15mm, the furthest away can take a couple of mins for the shower to come hot.  Pipe length and volume all have an effect on hot water delivery time.

 

OK, that is good to know. I assumed that is the case from different discussion I have had.

 

The 28mm was mentioned in a few articles I have read.

 

We are basically trying to figure out how to improve and those were the points we could find.

[Woze]

2 hours ago, ProDave said:

Where is the hot water tank in relation to the bathrooms?

 

There is a trend for heat pump installers to fit the hot water cylinder right close to where the heat pump pipes enter the house, in many cases a very long way from the point of use.

 

any plumber worth his salt would be advising put the HW cylinder as central as possible to the points of use to minimise the length of pipe and then use thinner pipe like no more than 15mm to minimise the volume of water that must pass through before the hot water arrives at the tap.

 

The hot water tank is below the shower, maybe 3m over from the tap. So not too bad.

 

Thank you for the comment on pipe size.

[ReedRichards]

22 mm copper pipe has an internal diameter of 20.2 mm.  Therefore a 1 m length of pipe holds 1.28 litres of water (if I have done my maths correctly).  Suppose your shower has a low flow rate of 10 l per minute of hot water.  If it takes 2 minutes to get hot water then your pipes must hold 20 l so the length of your pipe run is 15.6 mm.  That's very long but it's not impossible if your pipes don't follow a direct route.  If your hot water flow rate is higher then the length of the pipe run would be lower.  This is a plumbing issue and nothing to do with your heat pump.

 

If by "return pipe" you mean a hot water secondary return then that is by no means a standard plumbing feature unless you're a hotel.  If your hot water pipes are really 22 mm in diameter that is good for filling a bath quickly and bad for any other requirement.  I think 28 mm pipes are recommended between the heat pump and the cylinder (or is it the buffer tank) but not elsewhere.  If your hot water pipes were 28 mm then your problem would be even worse.  

 

      

Edited February 24, 2023 by ReedRichards

[Woze]

On 24/02/2023 at 23:03, ReedRichards said:

22 mm copper pipe has an internal diameter of 20.2 mm.  Therefore a 1 m length of pipe holds 1.28 litres of water (if I have done my maths correctly).  Suppose your shower has a low flow rate of 10 l per minute of hot water.  If it takes 2 minutes to get hot water then your pipes must hold 20 l so the length of your pipe run is 15.6 mm.  That's very long but it's not impossible if your pipes don't follow a direct route.  If your hot water flow rate is higher then the length of the pipe run would be lower.  This is a plumbing issue and nothing to do with your heat pump.

 

If by "return pipe" you mean a hot water secondary return then that is by no means a standard plumbing feature unless you're a hotel.  If your hot water pipes are really 22 mm in diameter that is good for filling a bath quickly and bad for any other requirement.  I think 28 mm pipes are recommended between the heat pump and the cylinder (or is it the buffer tank) but not elsewhere.  If your hot water pipes were 28 mm then your problem would be even worse.  

 

      

 

Thank you, that is a very thorough estimation. I would estimate the pipe in question to be 8m, so roughly half.

Our water pressure is quite low compared to previous experience - or compared to neighbours.

I always assumed the ASHP doesn't take away from the water pressure, so not sure anymore what the culprit might be.

 

What I am mostly annoyed about is less the inconvinience but more about how much water we will be wasting in the long run...

 

[ProDave]

With all the pipes cold, run the hot tap collecting it's output in buckets, jugs etc, and measure the amount of cold water that comes through before the hot water arrives.

 

Some plumbers don't understand this issue.  I remember refurbishing my first house, my father was the plumber doing it. Installing a new bathroom in the opposite corner of the house to the HW tank.  Dad ran 22mm from the tank to the bath tap and then a 15mm branch from that to the basin tap.  I argued with him but just could not get him to accept that running a separate 15 or even 10mm from the tank to the basin hot tap, would waste less hot water getting it to the tap.

[ReedRichards]

7 hours ago, Woze said:

I always assumed the ASHP doesn't take away from the water pressure.

 

 

That's absolutely correct.  The ASHP heats water in a cylinder and has no influence whatsoever on the water pressure (the same would be true however your cylinder is heated).  If your cylinder is unvented then your hot water pressure should be set to something approaching the pressure of your mains cold water.  However if you have a narrow (15 mm) pipe from your rising main to your hot water cylinder that could restrict the hot water pressure. 

[Woze]

Thanks a lot

35 minutes ago, ReedRichards said:

 

That's absolutely correct.  The ASHP heats water in a cylinder and has no influence whatsoever on the water pressure (the same would be true however your cylinder is heated).  If your cylinder is unvented then your hot water pressure should be set to something approaching the pressure of your mains cold water.  However if you have a narrow (15 mm) pipe from your rising main to your hot water cylinder that could restrict the hot water pressure. 

 

OK, Would need to check that.

 

There is a distinct difference from hot water to cold water pressure which should be one indicator of the issue

[Woze]

2 hours ago, ProDave said:

With all the pipes cold, run the hot tap collecting it's output in buckets, jugs etc, and measure the amount of cold water that comes through before the hot water arrives.

 

Some plumbers don't understand this issue.  I remember refurbishing my first house, my father was the plumber doing it. Installing a new bathroom in the opposite corner of the house to the HW tank.  Dad ran 22mm from the tank to the bath tap and then a 15mm branch from that to the basin tap.  I argued with him but just could not get him to accept that running a separate 15 or even 10mm from the tank to the basin hot tap, would waste less hot water getting it to the tap.

 

Thank you, I was thinking of doing that.

 

Also good point on the pipe sizes - will check on that as well.

 

Thanks a lot - that has been very helpful already

[ReedRichards]

2 hours ago, Woze said:

There is a distinct difference from hot water to cold water pressure which should be one indicator of the issue

 

Do you actually have an unvented hot water cylinder (in which case there should be a pressure vessel nearby) or is it vented (in which case there will be a header tank in you loft and not so much hot water pressure)?

[Woze]

10 hours ago, ReedRichards said:

 

Do you actually have an unvented hot water cylinder (in which case there should be a pressure vessel nearby) or is it vented (in which case there will be a header tank in you loft and not so much hot water pressure)?

 

There is a pressure vessel nearby so assume it is an unvented hot water cylinder...

[ReedRichards]

In which case you should be able to achieve hot and cold water at similar pressures.  

[JohnMo]

From cold water in the pipe and hot water in the cylinder and opening the tap several things occur before you get perceived hot water out.

 

You open the tap, preheated water flows from cylinder, displacing cold water, the hot water is diluted with cold and at the same time cooled by the cold copper pipe.  This will continue along the pipe until the copper pipe heats up, if the pipe is uninsulated the heat will also heat the air around the pipe.  You will then start to hot water out the tap.

 

The bigger the pipe the bigger the volume of water, the larger the area of copper, the larger the area to radiate heat.

 

You seem to be going down a rabbit hole looking at at flow rates and pressures.  Get yourself down to a local DIY store buy some lengths of insulation, if not already installed and install to the pipe run.  If that doesn't improve things your only options are, smaller pipe dia.  Or a secondary return circuit, ideally on a timer.

[Woze]

41 minutes ago, JohnMo said:

From cold water in the pipe and hot water in the cylinder and opening the tap several things occur before you get perceived hot water out.

 

You open the tap, preheated water flows from cylinder, displacing cold water, the hot water is diluted with cold and at the same time cooled by the cold copper pipe.  This will continue along the pipe until the copper pipe heats up, if the pipe is uninsulated the heat will also heat the air around the pipe.  You will then start to hot water out the tap.

 

The bigger the pipe the bigger the volume of water, the larger the area of copper, the larger the area to radiate heat.

 

You seem to be going down a rabbit hole looking at at flow rates and pressures.  Get yourself down to a local DIY store buy some lengths of insulation, if not already installed and install to the pipe run.  If that doesn't improve things your only options are, smaller pipe dia.  Or a secondary return circuit, ideally on a timer.

 

Unfortunately, the pipes are already behind closed walls. We had full trust in the system until we started living in it.

 

I will inquire about insulation to the pipes though, that should have been done for sure.

 

We need to see what can be done at this stage...

 

Thank you!

 

[ReedRichards]

I used to have a Combi boiler and a very long pipe run.  There used to be a long wait to get hot water with enough flow to fill at least one bucket of water but when the hot water came it was immediately hot, not tepid and warming up slowly.  So I don't think there was significant mixing in the pipes nor time for the cold pipes to significantly cool the hot water.  Therefore I don't think @JohnMois correct in his account of the sequence of events, I don't think cold pipes and possible lack of insulation will kick-in significantly until you turn the tap off, they will determine how rapidly the water that is then trapped in the pipes will lose heat.

 

If you had a thermal imaging camera you could look at the pipes inside a wall and see how rapidly they heat-up when hot water flows through them.  The faster you see them get hot, the less insulation they have.      

[JohnMo]

1 hour ago, ReedRichards said:

hot water came it was immediately hot

Well you must have had a magically boiler, my last house and current house, the water flows cold, then warms up over a few seconds then becomes hot.

[ReedRichards]

3 hours ago, JohnMo said:

Well you must have had a magically boiler...

 Possibly not, but if you have been running cold water into a bucket for long enough to fill the bucket and start on a second one then, in order not to freeze your hand, you only test the water temperature every few seconds.  Whatever happened, the amount of time in which the tap may have run warm rather than hot was insignificantly short compared to the amount of time it ran cold.

 

I was so traumatised with my old bad plumbing that I installed a secondary return loop for my hot water, even thought the pipe runs were shorter from the new hot water cylinder.    

Edited February 28, 2023 by ReedRichards

[Marvin]

Hi @ReedRichards

 

A 22mm copper pipe has an internal volume of about 0.31 litres per meter.

 

Three meters between tank and shower? There's something wrong. In my humble opinion, either long pipework or low pressure or low temperature, or lack of insulation or shower controls interfering.

 

M

[ReedRichards]

Hi @Marvin

 

I fixed my problem; it's @Wozewho has the issues now.  They seem to have been badly let-down by their plumber who has installed or perpetuated some very odd pipework.  

[Woze]

On 01/03/2023 at 07:41, Marvin said:

Hi @ReedRichards

 

A 22mm copper pipe has an internal volume of about 0.31 litres per meter.

 

Three meters between tank and shower? There's something wrong. In my humble opinion, either long pipework or low pressure or low temperature, or lack of insulation or shower controls interfering.

 

M

 

Thank you, that's good input - our problem is that nobody is trying to figure out the issue or is willing to admit a fault.

We are currently trying to find some sort of independent surveyor to assess what's wrong...

[Woze]

On 01/03/2023 at 08:48, ReedRichards said:

Hi @Marvin

 

I fixed my problem; it's @Wozewho has the issues now.  They seem to have been badly let-down by their plumber who has installed or perpetuated some very odd pipework.  

 

To be fair, we don't know who is at fault. The ASHP installer didn't advise the plumber on the requirements apparently so they just did what they always did. One could assume the plumber might ask but he didn't.

 

On the other hand we were advised that under the certification scheme it is a requirement for the ASHP installer to advise the plumber on the system needed. That did not happen

 

[ProDave]

11 minutes ago, Woze said:

To be fair, we don't know who is at fault. The ASHP installer didn't advise the plumber on the requirements apparently so they just did what they always did. One could assume the plumber might ask but he didn't.

If the ASHP installer just connected the HP to the HW tank in a location not chosen by him, then he is not at fault.

 

It still sounds like an excessively long pipe run.  Did you ever do that test when cold, measuring just how much cold water comes out of the tap before the hot water arrives?

[Woze]

3 minutes ago, ProDave said:

If the ASHP installer just connected the HP to the HW tank in a location not chosen by him, then he is not at fault.

 

It still sounds like an excessively long pipe run.  Did you ever do that test when cold, measuring just how much cold water comes out of the tap before the hot water arrives?

 

The entire system had to be replaced. HW tank and everything was installed by him/his company.

 

It physically can't be that long. Will do that test in the coming days and see how much it is.