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Author Topic: Massive electric use ... Help  (Read 1776 times)
AndyP
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« on: February 22, 2021, 11:02:27 PM »

Hi
We have a Danfoss DHP-L 16kwh gshp in our 3 storey old stone farmhouse and although the ufh works well, the radiators upstairs struggle. Weíve had an engineer out a couple of years ago as we kept getting high pressure alert but that seems to be resolved, however weíve gone from approx 20,000 kWh in 2015 to just under 30,000 kWh last year, not sure if/what changes the engineer did to control panel but last week during the sub zero temperatures we were using between 170-200 kWh per day! Cannot afford this. Kids homeschooling with coats on upstairs is not a good thing. I have looked at elec usage over the last few winters and some months we are using between 3-4,000 kWh per month.
I know the house is big and we would obviously have a significant electric bill but cannot figure out how we are using 10,000 kWh extra. Not really sure how the heat curve / heat stop work or which adjustments will reduce bill but feed rads. Unfortunately I was at work when everything was fitted and the company (now in liquidation) didnít do a great handover.
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Philip R
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« Reply #1 on: February 22, 2021, 11:37:00 PM »

AndyP, welcome to the forum.

Please tell us about your installation. What preceded it,  if anything, and the reasoning behind the change to the heat pump. Can you tell us if your heat source consists of boreholes or slinky coils.,  if the latter, what ground area do they cover.  Also typical brine flow and return temperatures, also heating system flow and return temperatures. Is there an electric resistance heater in the heat pump working as a permanent feature? this could part explain the large energy consumption.

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JohnS
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« Reply #2 on: February 22, 2021, 11:44:12 PM »

My first suggestion is to try and correlate your usage with weather conditions.  Winters vary between cold and mild.

Do you have weekly or monthly meter readings?  Great help if you did.

There are websites which give you heating degree days for various locations in the UK.  They assume that with an outside temperature of 15.5 deg Centigrade you don't need to heat your house.  The internally generated heat from people, appliances, cooking, sunshine into windows, etc will be sufficient.  For each degree and day that the temperature is below 15.5, you will need a set amount of heat, and thus electricity.

From about 2008 to 2014, I closely monitored weekly gas consumption with degree day data and found a strong correlation with consistent improvements as I enhanced draft reduction, improved insulation and installed better heating controls.  Outlying data could easily be explained, eg half term week and kids at home or away for a couple of days, grand parents staying and therefore house needed to be a degree or two warmer, etc.

Unfortunately, if you don't have good consumption information, I am not sure where one would begin to look.

Except to say that heat pumps and poorly insulated buildings don't go well together.

If you have good correlation, it might just be because the last couple of years have been quite mild.  If the correlation is poor, it    
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kdmnx
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« Reply #3 on: February 23, 2021, 07:17:03 AM »

Heat pumps and draughty or poorly insulated buildings donít go together. How deep is the insulation below the slab? I guess you fitted IWI, how thick? Did you have your air leakage professionally measured?

What is the make/model/size of heat-pump? Many are undersized and therefore use their auxiliary resistive heating element excessively. If the rads upstairs arenít big enough then the feed temperature is probably set to a level that dramatically reduces the efficiency of the HP. How was your borehole / trench sized? A common problem is an undersized hole/trench resulting in the HP quickly exhausting the available heat from the ground, particularly if the trench isnít deep enough.

Many people with a HP use biomass for the coldest months. Is this an option for you?
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marshman
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« Reply #4 on: February 23, 2021, 08:36:17 AM »

The key point is that energy use seems to have jumped by 50% after the engineer came.  It was apparently working OK before - have I got that right?  If so then I doubt there is something fundamentally wrong with installation, insulation, ground loop install etc.

The Danfoss DHP L I think is similar to my Thermia Diplomat.

It is very easy to get it to "eat" 50% more electricity by just "adjusting" the settings slightly.


First question.

1.   Does it provide your domestic hot water as well? if so double check that the auxiliary electric heating is OFF. The heatpump alone should get the water to 55 deg C, mine does and we find this is perfectly adequate for our needs. It can be programmed to do a weekly legionella cycle if you are concerned about such things.  Incidentally the maximum temperature of the hot water is "controlled" by the fact that the compressor trips out on maximum pressure !!!   So that leads me on to the second question.

2. How did you know it was tripping due to max pressure,  i.e. what was on the display when it was "tripping out initially"?

3. What controls your system?  is it controlled on an internal thermostat or do you let the heatpump controller and Room / Heat Curve regulate the temperature?  If I raise the heat curve on my system by just one degree then as a rule of thumb energy use increases by over 10%.

For clarity my pump is a 10kW Thermia Diplomat- (I think Danfoss were effectively rebadged Thermia units) heating  a largish  (240 sq m)  old farm house via UFH and it also does the domestic hotwater via a 300 litre tank. We are retired so here all the time, the whole house is warm 24/7. Been installed for over five years and careful tweaking & improvements to house insulation and draught proofing has brought annual energy use down as follows:

year 1   1800kWh      2015/16
year 2   1700kWh      2016/17
year 3   1550kWh      2017/18
year 4   1250kWh      2018/19
year 5   1340kWh      2019/20
year 6   1150kWh      2020/21  estimated - still 2 months to go but only 830 kWh so far this heating season.

As you can see the initial consumption was around 40-50 % higher than it is now.

The real key is longer runs at lower flow temperatures. Avoid at all costs using it like a normal boiler where it is switched on and off via a timer and has to try to heat the house up from cold.

So first step look to see if the auxilary electric heating is turned OFF.  Then look at your other settings - can't remember what they all are at the moment.

You could also contact Ashgrove (they are (or were) the UK agents for the heat pump) and ask the for the default settings for your unit if you don't know and then tweak them from there.   To be honest the main ones are just the Room Temp and The Heatcurve and heat curve compensation settings.

Roger
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djs63
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« Reply #5 on: February 23, 2021, 09:09:47 AM »

 Echoing marshman, turn off any extra electrical heating if it is on. The engineer may have activated this. As marshman says, if the setup was using a lot less electricity before the engineer came then perhaps he turned on something.

Also, gradually tweaking the settings and keeping a record are the best approach. snow
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« Reply #6 on: February 23, 2021, 10:09:42 AM »

Marshman +1

The take home is that you are using 10 to 15 times more leccy than Roger and therefore need to start insulating and then insulating some more.


Make sure the HP is running 24/7 at lowest temp you can get away with. Switch off any leccy boost and store hot water at 50C max.

What HP outlet temps are you seeing?

Ken
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AndrewE
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« Reply #7 on: February 23, 2021, 11:39:49 AM »

The take home is that you are using 10 to 15 times more leccy than Roger and therefore need to start insulating and then insulating some more.
Ken
and draught-proof everywhere, then do that again too!
My victorian semi has really benefitted from us fitting modern but look-alike sash windows, brass spring strip draughtproofing round the doors and (almost) sealing off the chimneys in each room.
It's getting to the stage where I am considering installing a heat-recovering mechanical ventilation system to take out the humidity which used to condense on the thin glass of the old sash windows.
A
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marshman
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« Reply #8 on: February 23, 2021, 01:02:47 PM »

The take home is that you are using 10 to 15 times more leccy than Roger and therefore need to start insulating and then insulating some more.
Ken
and draught-proof everywhere, then do that again too!
My victorian semi has really benefitted from us fitting modern but look-alike sash windows, brass spring strip draughtproofing round the doors and (almost) sealing off the chimneys in each room.
It's getting to the stage where I am considering installing a heat-recovering mechanical ventilation system to take out the humidity which used to condense on the thin glass of the old sash windows.
A

I agree on the point of insulation etc. BUT all that is secondary to the question of why electricity consumption had increased 50%   Yes it is high but a 50% increase on an already high figure is a lot !!
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« Reply #9 on: February 23, 2021, 03:13:56 PM »

I think it is all part of the same picture. The excessive electricity consumption is likely caused by the HP making excessive use of its resistive heater, or the flow temperature being set too high. However, insulation and draught-proofing is the way the restive heating element will no longer be used and the flow temperature can be set lower.
« Last Edit: February 23, 2021, 05:49:06 PM by kdmnx » Logged

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brackwell
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« Reply #10 on: February 23, 2021, 04:59:33 PM »

A HP 50% the size of proper design requirement is sufficient for 90% of the time but what happens when the HP cannot supply enough heat whatever happens?  This is easyly reached when the ambient drops dramatically, the output drops and the COP big time. 

I suspect the OP said to the engineer that the rads were not providing enough heat (probably because they are too small as they nearly always are) so the engineer just turns up the water temp a bit and the increase in leccy consumption only increases a little  UNTIL you get to the point that the HP cannot cope and then it hits the fan.  The leccy element backup is now on nearly all the time and the defrosting is on a lot and the leccy bill goes through the roof. I am not surprised at 50% increase in leccy.

Salespersons selling undersize HPs with undersize rads will be the doing of HPs and all because the customer would baulk at the cost.

The same thing happened at Home Farm last cold spell for those that follow it.
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AndyP
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« Reply #11 on: February 23, 2021, 11:59:06 PM »

Hi all and thank you for your thoughts.

We have a Danfoss DHP-L 16kwh 3 phase GSHP. it has a DWH 300 litre hot water tank and a 210 litre buffer vessel. we have 3x250m 40mm HDPE ground loops buried in a sand bed on heavy clay soil 1 metre deep by 1 metre apart.

The house footprint is approx 330 sq metres, 3 floors and 7 occupants currently ageing 9-48!

The house was gutted in 2007/8 leaving the exterior stone walls approx 1/2 metre thick, standing. Not sure if insulation under floor slab but definitely on top to allow for ufh, which works well. To my knowledge the roads are oversized as we followed all advice but not sure how weíd check?, they seem to work when they feel like it!

All new internal/external walls and ceilings insulated. Unfortunately we have since discovered the polystyrene insulation sold to my father in law is useless and we now have to reroof with the extra fun of removing the solar pv panels 😞😞but that doesnít explain why elec has gone up by 10,000 kWh in 4/5 year period.

I have monthly reads from August 2018, (could get years earlier if necessary) when we first noticed elec usage rising, but itís since September 2019 that itís jumped, around this time we kept getting the trips which said High Pressure Alarm on control panel.

It was when we hit 5198 kWh for December/January just gone that we knew something was up. Foolishly put the ££ down to elec price rise before this, not noticing monthly usage.

Iíve been taking daily readings since 4 February when outside temperatures were consistently well below freezing for a week and the usage was between 129 and 198 kWh per day.

Iíve been taking morning and evening readings since 15 February and we have been using between 81-109 units, but outside temperatures are significantly higher. Using between 45-87 units overnight, presumably because of nighttime temperature drop.

On 17 February I recorded the following:

Heat Curve. 50C
Min.            20C
Max.           55C
+5.              0C
0.                0C
-5.               1C
Heat Stop.   24C
Reduction.     2C

Outdoor.        5C
Supply Line.  30 (48)C
Return Line.  30 (50)C
Hot water.     48C. Although I have seen this fluctuate?
Integral.       -800 also seen this fluctuate?
Brine In.         5C
Brine Out.       5C

On 21 February changed Heat stop to 20C, used 87 units in 24hr period, relatively mild day/night
On 22 February changed to 18C, used 94 units in 24hr, but colder overnight by 6 degrees

Following your thoughts we have turned the system to  Heat Pump only (system was on auto) at 10pm 23/02 and taken an elec read.

No 2 child still complaining of no heat in rads, but bedroom is at farthest point from pump.

We are not convinced the engineer was entirely sure of what he was doing when he pressure flushed the system and fitted a pump on the flow pipe to reduce the pressure on the heat pump, thereby reducing the frequency of the trip.

Up until I reduced the Heat stop we frequently had the lightening bolts 1 or 2 coming on the panel.

Thanks
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AndyP
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« Reply #12 on: February 24, 2021, 12:13:55 AM »

Forgot to ask, will we have enough hot water to shower all of us and how do we make sure the legionella process takes place having turned it to heat pump only
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« Reply #13 on: February 24, 2021, 01:13:03 AM »

Will write a more detailed response tomorrow morning but a couple of observations/comments:


1. Can you provide readings from when the heat pump has actually been running for 5 minutes. The pump was not running when you took those readings as the brine in and out temps were the same.
2. Setting it to heat pump only rather than auto I think stops hot water production, will check that in the morning,but I guess you will soon find out.
3. Heatstop setting is the outside temperature where the heat pump will not turn on, i.e. summer! It will have no effect at this time of year.

4. The Heat curve set at 50 is the reason for the high consumption compared to mine. My Heatcurve is set to 32 I think, will check tomorrow.


Roger
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DoItDreckly
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« Reply #14 on: February 24, 2021, 09:55:50 AM »

If the pump was running at the time of your readings then the brine is not being used at all. It is all on resistive heating. There should be a drop in the brine temperature. Is the heat pump in the garage?  If inside the heated envelope the brine readings would usually get to the ambient temperature depending on sensor position of course.

When I worked out the loop size for my old stone house (150m2) I required 750m so your loop feels a bit undersized. Granted it was N Scotland but even so.  We have about 6000 kwh usage a year and are purely running on radiators.

You could oversize the radiators in the rooms that feel cold.
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