LG Therma V mono block Air Source Heat Pump

[dpmiller]

it's 30kw until the flow temperature reaches setpoint.

[ReedRichards]

Okay, 30 kW until the flow temperature reaches the set point of 80 C (say) versus 12 kW until the flow temperature reaches the set point of 50 C (say).  Which gets to the set point the fastest?  

[dpmiller]

But how do you know when the oil unit has reached setpoint? Short of going and checking if the burner is running? Rads will be putting out noticeable heat well below that.

 

The oil unit is totally uncontrolled, the ASHP will only be putting out it's full 12.5kW *if* the heating load keeps the return temp low and as previous it wants to keep the flow deltaT within limits as well.

 

It's the same house with the same heatload. The oil boiler will heat it more rapidly.

[ReedRichards]

So are we saying that when the radiators are cold they won't give out as much heat so the delta T between flow and return will be less?  The heat pump cares about this so modulates its power down to control delta T whereas an oil boiler would go at full power until the return water gets too hot?

 

These are the first three power cycles my ASHP goes through, starting when it comes on at 7 am and showing the first hour until 8 am.  Thereafter most cycles are like the last one in shape.  The power consumption certainly rises to a peak and then goes down.

 

 

 

 

 

      

[dpmiller]

precisely.

[Ronny]

I have a totally different question in regards to radiators. I kept the existing radiators when the heat pump was installed, as they were all double convectors and oversized, except bathroom and kitchen due to space constraints. I have been looking at low water content fan assisted radiators which unfortunately are very expensive. The cheapest i have seen are Smiths eco-powerad fan convectors. The water content is approx 0.5 liter so should shorten the time to heat the system from cold. Does anyone have these or similar as i would like to know more before buying one to try in the kitchen. As an aside, now that it is spring, my heating is on from 08.00 to 19.00, set to AI and the total usage including cooking is just under 14kwh which i am very happy with. 

[ReedRichards]

@Ronny, don't you have a meter measuring just your heat pump usage?  I had to have one fitted as a necessary condition to get RHI payments but I find it pretty useful, particularly as I have solar panels so my main meter reading does not tell me how much electricity I have used.

 

I would be concerned about noise from fan-assisted radiators.

[Ronny]

7 minutes ago, ReedRichards said:

@Ronny, don't you have a meter measuring just your heat pump usage?  I had to have one fitted as a necessary condition to get RHI payments but I find it pretty useful, particularly as I have solar panels so my main meter reading does not tell me how much electricity I have used.

 

I would be concerned about noise from fan-assisted radiators.

Yes I have meter but would need to remember to read it every day to have daily readings. The access to the meter which is fitted beside the tank is from outside, it is in the old coal store built into the side of the house. The only place where I would but a fan assisted radiator would be in the kitchen ,so noise would not be a problem. 

[ReedRichards]

I have been looking at the settings that control the AI mode; I have not changed these myself so they are either defaults or input by my installer.  These are:

Outdoor temperature for auto mode:  Min 5  Max 19

LWT for auto mode Min 34  Max 50

 

My heating is all radiators hence the 50 C max LWT but do other set-ups use similar parameters?

 

[Ronny]

5 hours ago, ReedRichards said:

I have been looking at the settings that control the AI mode; I have not changed these myself so they are either defaults or input by my installer.  These are:

Outdoor temperature for auto mode:  Min 5  Max 19

LWT for auto mode Min 34  Max 50

 

My heating is all radiators hence the 50 C max LWT but do other set-ups use similar parameters?

 

I have checked my settings and are as follows:

Outdoor temp for auto mode min -7 max 21

LWT for auto mode min 34 max 46

Some of these settings were changed by me and were left as i set them as they did not appear to make any difference.

I really need to wait for winter now as i understand more about the system now than i did. I have been using the AI setting the past few weeks and when it comes on at 07.45 it heats the house up to about 19.5 deg and does not come back on all day. I assume there is very little heat loss. I have been spending a bit of time trying to analyze my octopus go account.and one thing stands out. My in home display is showing the daily spend far in excess of the actual from octopus. The IHD was showing as much as nearly £6 a day when very cold, but the max from octopus was £3 a day. This makes a big difference to my perceived dailly costs which were at times alarming. I could not check this during the winter as the first account from Octopus was for a 3 month period. I only moved to Octopus in February and the way they breakdown the account is the best i have seen. Each day has a graph and consumption reading every half hour. There is little doubt in my mind that i will be very close to the same costs as i had using the combi boiler. Time will tell, and i will update this next year !!!!!!!

[ReedRichards]

As I now understand the AI mode, if the outdoor temperature is between the min and max settings then the LWT is decreased linearly from the max to the min setting.  For example, In your case @Ronnyif the outdoor temperature was half way between -7 and 21, which is +7, then the LWT would be 40, which is half way between your min and max settings.  Since it is very rarely as cold as -7 or less, your LWT would very rarely get as high as 46.  

[SteamyTea]

@Ronny @ReedRichards

Not been following your sub discussion on the AI.

Are you saying that when it is turned on, the LWT (Lower Water Temperature) drops lineally with outside temperature (so when -7°C outside, LWT is 34°C, than at 21°C it is at 46°C).

Or are you saying that it is the inverse of this? (so when  -7° the LWT is 46°C and when 21°C it is at 34°C).

I assume the MWT (Maximum Water Temperature) is allowed to float as long as it is greater than the LWT).

[Ronny]

I have been trying to upload a pic of the heat pump and tank with no luck. I will try this time using my phone

[dpmiller]

1 hour ago, SteamyTea said:

@Ronny @ReedRichards

Not been following your sub discussion on the AI.

Are you saying that when it is turned on, the LWT (Lower Water Temperature) drops lineally with outside temperature (so when -7°C outside, LWT is 34°C, than at 21°C it is at 46°C).

Or are you saying that it is the inverse of this? (so when  -7° the LWT is 46°C and when 21°C it is at 34°C).

I assume the MWT (Maximum Water Temperature) is allowed to float as long as it is greater than the LWT).

 

 

Inverse, ST. Bog-standard weather compensation, in other words?

[Ronny]

3 hours ago, dpmiller said:

 

 

Inverse, ST. Bog-standard weather compensation, in other words?

I think you are correct with your statement. I am the first to say I am at times bamboozled with what a lot of the settings do, or are meant to do. I am old so at least I have an excuse. I am hoping when winter comes around, I will be able to run AI mode and perhaps be able to run the system constantly, at reasonable cost and comfort level.

[SteamyTea]

5 hours ago, dpmiller said:

 

 

Inverse, ST. Bog-standard weather compensation, in other words?

Thanks, it is what I thought.  Can kill the CoP if there is a long spell at around 4°C, and cause extra defrost cycles, but hopefully you make that back when the temperature is higher.

So the trick is to design your space heating system to run at as low a flow temperature as possible for the local climate, even if this mean an anti-intuitively, disproportionately oversized ASHP.

[ReedRichards]

On 28/05/2021 at 15:14, SteamyTea said:

@Ronny @ReedRichards

Not been following your sub discussion on the AI.

...

Or are you saying that it is the inverse of this? (so when  -7° the LWT is 46°C and when 21°C it is at 34°C).

 

 This is how it works, as @dpmillerstated.

 

@Ronnyis that a Telford cylinder (like mine)?

[Ronny]

7 minutes ago, ReedRichards said:

 This is how it works, as @dpmillerstated.

 

@Ronnyis that a Telford cylinder (like mine)?

The cylinder is a world heat 150 L superflow  The biggest I could get into the available space.

[ReedRichards]

Ah, different company but also made in Manchester.  It was the bee logo I recognised as my cylinder also has one - but I now think that to be a Manchester branding.

[Ronny]

On 30/05/2021 at 22:17, ReedRichards said:

Ah, different company but also made in Manchester.  It was the bee logo I recognised as my cylinder also has one - but I now think that to be a Manchester branding.

From what i can see of your cylinder it looks identical to mine. Perhaps they sell the same thing under different brand names. I can only see a small portion of yours in the picture you uploaded.

[dpmiller]

A lot of the componentry will be the same, and (no doubt) there are only so many suppliers of the wee rubber trims for around the pipes, and the plastic top/bottom covers...

[ReedRichards]

I noticed that at the bottom of the cylinder there is a unconnected immersion heater, the same thing that I have.  In my case the bottom section is the buffer tank.  At the moment I have solar electricity to spare and I was wondering what would happen if I used it to heat the water in the buffer tank via its immersion heater.

[SteamyTea]

1 hour ago, ReedRichards said:

At the moment I have solar electricity to spare and I was wondering what would happen if I used it to heat the water in the buffer tank via its immersion heater.

I would have thought it would act as normal, temperature is temperature. The only thing I can think of is when the heater is on, and a little time after, the base of the water column will be hotter than normal. This may affect the flow temperature to the UFH, but probably not a serious issue.

Connect it up and fire it up, be interesting to see what it does.

[Ronny]

Surely using this element to heat the buffer tank would be a step backwards., unless you were having problems getting up to the required temperature due to extreme cold.  Out of interest, now that the heating is no longer required, i am using roughly 10 kw a day for hot water, cooking and all the other things plugged in 24/7. Is this what you expect for 2 people in house.

[SteamyTea]

9 hours ago, Ronny said:

Surely using this element to heat the buffer tank would be a step backwards

I think they want to take advantage of excess PV generation.

 

16 hours ago, ReedRichards said:

At the moment I have solar electricity to spare

 

No you are not, 10 kWh/day would be correct.

I used about 8 kWh/day when I had a lodger, now between 6 and 8 kWh/day. Though this is going to go up as I have a second job, so more uniform to wash.

Edited June 4, 2021 by SteamyTea