Would a bigger pump compensate for small pipes?

[Hogboon]

Around this time last year I posted about the poor performance of a recently installed LG heatpump at my home. The view at the time, both on this forum and from the installers, was that the heatpump’s 9kw capacity was insufficient to extract enough heat in cold weather to achieve a target temperature of 20º C in the house. ‘Cold’ at the time was hovering about freezing up to approx 5º C.

The 9kw heatpump was installed on the recommendation of a surveyor to whom the installer at the time subcontracted such work. This surveyor subsequently had his licence revoked by STROMA, the regulating authority and the installer sees to such surveys ‘in house,’ but on advice from LG the 9kw heatpump was replaced by a 14kw heatpump.

 

As the replacement was only installed last spring, the jury [me!] is still out as to its performance since the weather has been, and remains, so mild that the target temperature can almost be achieved by opening the windows! However, about a fortnight ago daytime temperatures dipped somewhat towards the norm [5-10ºC] for time of year here [Somerset] and during the few days it remained ‘chilly’ the heatpump seemed to me to struggle to attain the requisite temperature. Here is a record of a typical day when the heatpump is set to start [07:00hrs] till the house was 20ºC made on Nov 5^th when the outdoor temperature was about 7ºC.

5 Nov	00’	30’
7 a.m.	17.6	17.9
8 a.m.	18.3	18.7
9 a.m.	19.0	19.3	Shower at 09:00
10 a.m.	19.2	19.2
11.a.m.	19.6	20.0

 

This struck me as unspectacular to say the least! Realistically there seem to me only 2 possible explanations.

1             LG heatpumps are incapable of performing efficiently at temperatures below 10ºC.

2             The pipework is too small. When the heatpump was installed the existing 10mm microbore was replaced with 15mm

3             Some other reason!

 

A friend of mine recently renovated a 4 bedroom four-storey town house which was completely gutted. They installed a heatpump with 28mm pipework to the radiators.

Since heatpumps operate by delivering a larger quantity of water heated to lower temperatures than that from say an oil boiler, presumably the larger the diameter of pipe the better – especially bearing in mind that doubling the diameter of pipe more than doubles the possible volume. A solution for me, if the poor performance is indeed the result of too small pipes, could be to replace the 15mm pipework with say 22mm but at present I reject that on grounds of cost and disruption.

 

My question therefore is: might the same outcome be achieved by installing a larger circulation pump to increase flow? or could an additional pump be installed somewhere to achieve the same result? If the latter, where should the pump go? Should it ‘push’ or ‘pull’ or would that make no difference? i.e. push colder water towards the heatpump or pull heated water from the heatpump to the radiators. And how big a pump could I safely install to avoid damaging the joints etc in the pipework? The tank is a 210 litre unvented one made by World Heat Cylinders rated at 3 BAR max pressure. Would an image help?

Finally, I should add that I emphatically do not intend to tackle any of this work myself ! If anything is done it will be by the original installer. Many thanks for any help or advice.      

[ProDave]

I have an older model 5kW LG heat pump that has never missed a beat even one night last winter when it went down to -18

 

My LG heat pump was very particular on water flow rate.  On initial install it kept tripping out with a low flow error.  It was too late to change any pipework, so I fitted a second circulating pump to supplement the built in one and that increased the flow rate to satisfy the HP.

 

If yours is not tripping with a low flow rate error, then I doubt the problem is insufficient water flow.

 

What is the supply and return water temperatures from the heat pump when it is doing space heating?  And how is the heat delivered? Radiators or UFH?

 

The 3 bar rating of the hot water tank is the pressure of the hot and cold water that comes out of your taps nothing to do with the heating circuit that is usually a sealed system with it's own expansion vessel.

[J1mbo]

• How is the system configured in relation to flow temperature - weather and room compensated, or fixed temp?
• What was the energy loss calculated at?
• What does the EPC show as annual energy demand for heating?
• What is the sum of the output of the installed radiators at the design peak flow temperature?

Edited November 11, 2021 by J1mbo

[Luke1]

If I read your table correctly, it has taken 4.5hrs to increase room temperature by 2.5degrees?

 

If this is a UFH system then this seems very good in my opinion, in fact, even if this is for radiators then it also seems reasonable. 

Point 1 of J1mbo's post is very relevant. If the system is weather compensated only, there is a chance that the system is set to run at lower flow temperatures over much longer periods, and programming the heating to come on and off like a conventional boiler may not be appropriate. 

[Hogboon]

Thanks ProDave [hello again!], J1mbo and Luke1 for your comments. Taking them in order;

ProDave: I am not aware of any ‘tripping out’. Presumably if it did, I would be aware? The only info I get is from a more-or-less useless [as far as I am concerned!] LG ‘remote controller’. Image attached. However, when the image was taken the heating was already up to temp so I will take another snap tomorrow morning when it may show the in/out heating temps. Heating is by radiator only.

J1mbo: no idea about the configuration you refer to. Where would I find that? I can attach the EPC etc but as this was prepared by the same man who was subsequently ‘struck off’ for incompetence it may have errors.  Floor area is given as 176 m².

“Current primary energy use per square metre of floor area = 165 kWh/m² per year” – but this presumably referred to the previous heat supplied from oil combi-boiler.

Space heating demand: 16,184 kWh per year.

Water heating demand: 3,537 kWh per year.   

Total heat loss seems to have been 21,729 but from the same document:

          Energy required to heat property = 16,184 kWh

           Energy required for hot water = 3,537 kWh

MCS SCOP Heating 3.17 [whatever that is – but as it is highlighted in pink as is MCS SCOP Hot Water 1.75 I include it here.]

As for total radiator output I have several tables etc none of which mean anything to me, but one gives ‘Heat Loss Calcs’ as Power [W] 4442; Energy HP [kWh] 21,729; Energy Bio [kWh] 20,956. Tot output from a table called ‘Emitter Log’ is 6,099 W.

Does any of that answer any of your queries?

Luke1: I am interested that you think the performance of my system is good! Perhaps it is and I am expecting too much but I am simply guided by the manufacturers claims etc which included that their pumps work efficiently down to -35º C. My experience to date is that even approaching 0º the heatpump struggles to extract sufficient heat to attain or maintain a temperature of 20ºC. The heating here is not under floor [if that is what you mean by UFH] but from radiators only.

I am hazy about ‘weather compensated’ heating. What is it? Where/how can I tell if it applies? There is a Hive thermostat which controls the heating; hot water is controlled by the LG heatpump. “There is a chance that the system is set to run at lower flow temperatures over much longer periods.” How can I tell?

Your final point is also interesting; “programming the heating to come on and off like a conventional boiler may not be appropriate” As far as I am concerned, what is appropriate is what I want, not what LG want. I got rid of a perfectly good oil boiler in order to do my bit for the climate etc. For the same reason [carbon footprint etc] I do not want the heatpump coming on in the middle of the night when air temperatures are generally lower than during the day and thus a heatpump must run for longer to extract the same total amount of heat as is possible at a warmer daytime temperature. Apart from it using more electricity [which in UK is still generated with a considerable input from fossil fuel – e.g. 75% according to BBC] it also wakes me up! and running during hours of darkness it is of course unable to make use of the PV panels installed to help power it.

Many thanks again.       

   

[JohnMo]

When you replaced your oil boiler for ASHP, did the contractor also do anything to your radiators, or are they same as we're installed with the oil boiler.  It could be the radiators are slightly under sized to meet the warm up time you are expecting, as the circulation temperature will be lower with ASHP.

 

The easy fix is to operate you heating in a similar manner to UFH, that is long operating periods and water low temperatures. 

 

The house will loose a set amount of kW on a given day - normal central heating throws big chunks of heat at the radiators for short periods, ASHP, give smaller  chunks of heat for longer periods, the kW given to the house and lost by the house is the same in both cases.

[ProDave]

Okay, radiators operating at 32 degrees are going to feel tepid, if not cold.  They are not going to put much heat into the room.  I suspect you want the rads operating at more like 40 or 45 degrees.

 

I would start by turning the weather compensation function off, and running at a fixed flow temperature.  Then you can experiment with that temperature and see what works best.

 

Once you know for certain what radiator temperature you need in cold weather and not so cold weather, then you will have enough information to turn on the weather compensating function again if you want to.

[TonyT]

Quote- As far as I am concerned, what is appropriate is what I want, not what LG want. I got rid of a perfectly good oil boiler in order to do my bit for theclimate etc. 
 

But you have replaced a 25/30kW boiler with a 14 kW version so they don’t operate in the same manner due to different heat outputs.

 

 

[J1mbo]

Based on the EPC numbers the thermal load in the property is about 6.5kW. It seems like the emitters (radiators and any UFL) are slightly undersized at the configured flow temperature, being only 6kW according to the assessors calculations. But that is a small difference and can easily be remedied by increasing flow temperature.

 

Weather compensation (WC) is the adjustment of the radiator flow temperature based on outside air temperature. This increases the heat pump efficiency considerably as the flow temperature is lower for most the year. WC is based on a curve dictating the amount of flow temperature adjustment based on outside temperature along with configured minimum and maximum temperatures. Adjusting the curve and maximum temperature will enable the output from the radiators to be controlled based on the outside temperature.

 

The display appears to indicate that the system is working with 32°C flow (and 28°C return). This would tend to suggest that weather compensation is enabled and, given the difference across the heat pump, that the radiator circuit pump speed is perhaps a little low as the difference of 4K (assuming the radiator circuit is balanced) would be more when the radiators are hotter (i.e. when it's colder). The display also shows room temperature of 22°C. Some controllers will use this additional data point to further adjust the flow temperature, which increases comfort by reducing overshoot, reduces cost by further reducing flow temperature when possible to do so, and increases system responsiveness by increasing flow temperature when there is a large difference between the current and target room air temperatures.

 

The design flow temperature will be listed on the MCS certificate as this dictates the SCOP for the system in question based on the approved tables for the particular product, and also dictates the RHI payments for the EPC annual heat demand (of 16,000 kWh). This temperature is the hottest flow temperature that the system has been sized to produce to match the thermal loss of the property with the fitted emitters (radiators). In this case, the stated maximum flow temperature should provide 6kW or so of output from the radiators fitted, assuming the radiator system is balanced and the inside ambient temperature is about 20°C.

 

Based on the information presented it seems that the original HP was adequate and that the issue is some combination of incorrect WC curve, maybe spurious room temperature based flow temperature adjustment possibly caused by the control panel being somewhere 'warm', and to a lesser extent undersized radiators and possibly low water speed.

 

Finding the configuration is the most important step at this point. You are looking for configured min and max flow temperatures, the design flow temperature from the MCS certificate, the weather compensation curve setting, and if room and weather compensation are enabled of course.

 

HTH

Edited November 11, 2021 by J1mbo

[J1mbo]

Also as a very approximate check. How much oil did you use per year before having the heat pump?

[Pocster]

Misinterpretation of the title 

[J1mbo]

I found the installer manual here in case you don’t have it @Hogboon:

 

https://www.manualslib.com/manual/1580071/Lg-Therma-V-Ahuw096a3.html?page=124#manual

[J1mbo]

It seems a bit 'translated' and I'm not sure I really follow it.

 

My interpretation (fwiw) is that the system with the Hive controller attached should be set to "leaving water temperature" mode and water leaving temperature set via "Seasonal auto temp" as something like:

 

• Set point 1 - the flow temp on the MCS certificate (I guess 50°C) plus maybe 5°C (could also be LW1)
• Set point 2 - seems to be the minimum flow temp, go with 40°C (could also be LW2)
• Set point 5 - the outdoor air temp providing max flow, put -5°C in (could also be Out1)
• Set point 6 - the outdoor air temp providing minimum flow, put in +5°C (could also be Out2)

 

Be sure to write down all settings before changing anything. Installer code could be 1001. What's not clear to me is whether these are configurable directly or set via Out1, Out2, LW1 and LW2.

Edited November 12, 2021 by J1mbo

[Hogboon]

Here are images of the LG 'remote controller' and the Hive thermostat at start-up this morning.

 

JohnMo: Yes, three radiators with “output at flow (W)” = 316 were replaced with slightly larger ones with “output at flow (W)” = 433. I understand exactly the point you make in your last para.

ProDave: I am not fussed by the temperature of the radiators; it is the overall ambient temperature in the house that interests me. My only way currently of assessing this is to note the temperature recorded on the Hive thermostat.  

When you say “I would start by turning the weather compensation function off” how would I do that? [Don’t bother answering that for the moment as I will plunge into the various screens in the LG Remote Controller later on and see if there is anything like ‘Weather Compensation: ON/OFF’]

J1mbo: I think the original calcs were based on a flow temperature of 45º. As there is another sheet of similar calcs based on 55º with a line drawn through it I assume that whatever decisions were made were based on the 45º. But whether any of that was ‘correct’ at the time or now, bearing in mind the bloke behind the figures was apparently incompetent, I don’t know.  As for how much oil we used pre heatpump, the short answer is ‘can’t remember’ but it would probably have been between 1000 and 1500 litres. Will see if I still have any receipts etc but I doubt it. And thanks for the installer’s manual. And I will try and digest your further suggestions about set points etc later on. Cheers for now as I have to take my wife to the station. 

 

[J1mbo]

The oil use is consistent with 6kW load.

 

it seems to me that this is just a system configuration problem and the original unit was sufficient.

[Hogboon]

J1mbo - after several readings I feel I have a slightly better grasp on some of what you have written. [Slow learner here etc.] I already have something called 'The Owner's and Installation Manual' which bears little relation to the manual whose link you sent. The latter looks much more like 'the bizniz.' My 'manual' consists of 16 pages of English text repeated [presumably] 34 other foreign languages, including some I have never heard of. Hands up who speaks Srpski [is this Serbian?] or Shqip ! Anyway, thanks for the grown-up's manual most of which is beyond my comprehension. 

 

The next problem is the password for the LG Remote Controller. In my case it is not 1001 nor any other obvious possibility so I have contacted the installer for my password. 

 

Meanwhile it remains very mild here so the heatpump has less to do than me. I have just had to cut the grass. In November! Your final comment... 

 

4 hours ago, J1mbo said:

it seems to me that this is just a system configuration problem and the original unit was sufficient.

 

is a bit of a jaw-dropper. The original unit was inspected and tested by two senior engineers from LG. Assuming they were kept in the loop by the installer I wonder why LG did not point that out that? rather than sit idly by while the installer replaced the original unit with one nearly twice the size. One cynical answer might be "why should they care?"  

[J1mbo]

3 hours ago, Hogboon said:

The next problem is the password for the LG Remote Controller. In my case it is not 1001 nor any other obvious possibility so I have contacted the installer for my password. 

 

See here at 1m34s - LG Therma V R32 Monobloc Heat pump | Installer Setting Guide - YouTube Could still be the software version number.

 

Take a look at page 99, water heating temperatures. Maybe that's all that needs to be adjusted (min/max).

[Hogboon]

Brilliant! Many thanks J1mbo. Password is the default software number displayed bottom right. [I suppose I might as well let the installer know while I'm at it!] I'll have a good old rummage and see what is what and take note, as you suggested, of anything I change.

 

To conclude for the moment, am I right thinking that my brilliant idea of inserting a bigger circulation pump seems to have received a universal thumbs ?  

[J1mbo]

I don’t think the system needs a bigger pump based on the delta between flow and return.

[Hogboon]

Rummaging over I am proceeding with caution, especially in view of the caveat [below] contained in the pdf manual you sent me - and, be it noted, not supplied to me by either LG or the installer.

 

"...It must be set by the installation specialist with the installation license, and if it is
installed or changed without installation license, all problems caused will be the responsibility of
the installer, and may void the LG warrenty"

 

Your brought my attention in particular to page 99 [INSTALLER > Water Heating set temp] as being possibly relevant to my problem. Page 99 has an image of the LG Control panel with min/max temperatures below in a table. 

 

 

How is the max temperature of 65 set in the image whereas the range is stated as 57~35?

 

As you correctly deduced, the installation here was based on flow temp of 50ºC. Here is an image of my controller of the [INSTALLER > Water Heating set temp] screen.

 

 

Given that my 'problem' is the efficiency of this unit when the outside temperature is around freezing, should I alter either of the above? and if so to what value?

 

I need at least 2 'cold' days to test. According to a recent comment on BBC WS we have 'Icelandic' weather on the way with forecast temps of -8º which should do nicely! so I would like to be ready with my finger on the trigger. Day 1 will be with current settings; day 2 would be with whatever alterations to the above are suggested. 

 

The required outcome will be raising and maintaining the temperature in the house to 20ºC.

 

One other item caught my attention. On page 111

 

Heater priority
• Heater priority : determine electric heater and DHW tank heater on and off.
• Example : If Heater priority is set as ‘Main+Boost heater ON’, then electric heater and DHW
tank heater are on and off according to control logic. If Heater priority is set as ‘Boost heater
only ON’, then electric heater is never turned on and only DHW tank heater is on and off
according to control logic.
• In the installer setting list, heater priority category, and press [OK] button to move to the detail
screen.

 

Too much gobbledegook in there for me, but what I would like to prevent, if at all possible, is the immersion heater ever being used or 'on' unless I specifically turn it on with the one exception of the 'sanitising' procedure. Is that possible? 

 

Cheers for now. 

 

 

    

 

 

 

 

 

  

[J1mbo]

Great. Can you post what is currently listed for:

• Temp. sensor selection
• Pump frequency setting(RPM)
• Heating only mode
• Seasonal auto temp:
  • Outdoor 1, Heat
  • Outdoor 2, Heat

 

Re DHW: is the immersion is even connected to the heat pump? Or just straight to a switch in the usual way.

 

Based on my own system I'd be inclined to set min/max to 28°/55° but it's not clear to me how these settings interact with the seasonal auto-temp settings. Does 'Set Point 1' through 'Set Point 8' appear anywhere in the controller under/near seasonal settings?

 

Also, as noted previously the run time of the system needs to be enough. I think that the Hive will prevent the system using the interior temperature to adjust the flow temperature and therefore it will tend to be less responsive. For now, we need to match the heating curves to the property heat-loss and then worry about warm-up times and such later. On that basis, I'd be inclined to leave it running 24x7 at the moment.

[Hogboon]

My Installer settings differ somewhat from those in the manual you sent. For example the Pump Frequency settings (RPM) does not appear at all as  far as I can see on my control panel whereas in the manual it is immediately after CN_CC. So apart from confirming that the Temp. sensor selection = WATER I don't seem to have any of the info you request. Here, in case it helps, are the menu entries from my controller.

 

• 3 mins. delay
• Select temp. sensor
• Dry contact mode
• Central control address
• Pump test run
• Air heating set temp
• Water heating set temp
• DHW set temp
• Screed drying
• Outdoor temp for auto mode
• Indoor temp for auto mode
• LWT for auto mode
• Tank disinfect set 1
• Tank disinfect set 2
• Tank setting 1
• Tank setting 2
• Heater priority
• DHW time setting
• Use heating tank heater
• TH on/off var heating air
• TH on/off var heating water
• TH on/off var cooling air
• TH on/off var cooling water
• Heating temp set
• Cooling temp set
• Pump setting in heating
• Pump setting in cooling
• Forced operation
• CN_CC
• Pump capacity
• CN_EXT
• Anti freeze temp
• Add zone
• Use ext. pump
• 3^rd party boiler
• Meter interface
• Pump prerun/overrun
• Pump op. time
• IDU op. time
• Zone
• RMC master/slave
• Energy state
• Data logging
• Password
• LG Therma V config

 I see nothing about seasonal settings anywhere, nor any ref to set points. As for your question about the immersion heater, how can I tell? [I am not a plumber ! which may or may not be reassuring.] But I have an image of the tank which may or may not enlighten you. 

 

 

Let me know if you need another or different shot. Many thanks for your help thus far. 

 

[J1mbo]

@Hogboon - I've looked at some older threads and I think figured out the weather compensation settings. See here.

 

• Outdoor temp for auto mode - this defines the ends of the slope. Set min to -1°C and max to 12°C.
• LWT for auto mode - this defines the leaving water temperature, i.e. flow temperature, targets at the outside temperature points set above. Set min to 34°C and max to 55°C.

 

The logic is:

• at or above the max outdoor temp of 12°C, the heat pump will use a target flow temperature of 34°C. This may be too high and could result in overshoot, but start here.
• at or below the min outdoor temp of -1°C (usually the point at which the property heat loss will be calculated in the UK), the heat pump will use a target flow temperature of 55°C.
• In between (i.e. -1°C to 12°C), the heat pump will chose a flow temperature between 34°C and 55°C based on a straight-line between the two points.

 

The question is then how to activate this automatic mode, if @ReedRichards is still reading this forum perhaps he/she might be able to comment. I think the internal controller should be put in 'auto' mode and the desired temperature range configured in 'Indoor temp for auto mode' - probably min 18°C max 24°C or something like that. I suspect that this range is then used to control the offset that can be configured in the controller, in my example it would allow -3°C to +3°C, corresponding to room temperature targets of 18 to 24.

 

Based on the photo of the controller earlier, you should be able to see pretty quickly what impact changes have. Inlet/Outlet were 28°C/32°C with a target (top of screen) of 32°C. That target, and after some time the outlet, should change according to what's been set and the outdoor temperature.

 

The final consideration is the Hive controller. I suspect this is a big part of the problem. Anything with a TPI program is unsuitable for a heat pump with weather compensation as the TPI program will introduce short-cycling by design, which is the worst possible operating condition for a heat pump. My advice would be to replace it with LG's native controls. However, for now, just set it to something really high like 30°C all the time which will effectively eliminate the TPI as the room temperature will be so far from the target and let the heat pump weather compensation control the living space.

 

I really hope this helps. Please do let me know how you get on.

[Hogboon]

Many thanks J1mbo for the homework and advice. I have every hope that tomorrow some of it will make sense! but right now I am the wrong side of a bottle to make head or tail of anything much. One thing I find very perplexing is just how complicated and poorly understood [or in my case not understood at all] is the efficient configuration and running of heatpumps. And yet they are going to be needed literally in their millions. Surely manufacturers have a duty to get the job right? and make what is required and what these machines are actually doing more transparent. Shan't drone on now, but thanks again and I'll let you know what if any progress I make.  

[J1mbo]

You are right. There is definitely a market for a heat pump troubleshooting and configuration service, though getting a reasonable rate of pay for that might be a challenge. The current trend of smart heating with individual room control is another enemy of the heat pump, since around 20 litres of water are needed circulating per kW of output at all times to avoid short cycling too.

 

Longer term I suppose the products will have to evolve with higher compressor modulation ratios, enabling them to more readily match demand mid-season, and eliminate buffer tanks since many (most!) properties simply don't have the space for one given a DHW cylinder will be needed. And, there is no reason why the heat curves and pump speeds can't all be solved automatically with a continual feedback loop. All this manual configuration is representative I feel of the manufacturers not being software companies, it's a bit like the challenge the established automobile manufacturers are facing when compared to the new-entrants. It is obvious that the heat pump, with suitable interior sensors, can learn the heat curves needed with no user input and continually adjust these in relation to (for example) solar thermal gain.

Edited November 17, 2021 by J1mbo