GSHP - I need help with making it as efficient as possible!

QrizB

countryhouse39 said:

Can I check - when you ask about whether we are heating a swimming pool or something - how much electricity should it take to heat a full domestic HWT? Trying to get an idea of just how much over the expected we are…

Heating a 250-litre HW tank from 10C to 60C will take almost 15kWh of energy. That's how much electricity you'd need if you were using an immersion heater but with a heat pump it should be between 1/2 and 1/3 that much.

Put another way, if your heat pump is using almost 30kWh a day just to heat hot water, you should try switching the HP off and the immersion heater on.

Magnitio

countryhouse39 said:

Can I check - when you ask about whether we are heating a swimming pool or something - how much electricity should it take to heat a full domestic HWT? Trying to get an idea of just how much over the expected we are…

To heat a large hot water cylinder (210 litres) from 10C to 55C takes about 11kWh. However, your energy usage will depend on:

- the amount of hot water you actually use - a very large consumer could get through far more than 210 litres per day;

- the heat loss from the hot water cylinder (which can be 100+ Watts depending on the size and insulation of the cylinder);

- the efficiency of the method used to heat the water.

With 2 people in our house and a 117 litre hot water cylinder, we use on average about 4kWh per day for immersion heating.

Reed_Richards

According to a spreadsheet I made earlier it takes 5.83 kWh to raise 100 litres of water by 50 C.  That's more than the average 3 people would use per day so your house would need 15+ occupants or a hot tap left running somewhere to use about 30 kWh of heat.  If your heat pump can achieve a CoP of 3 then 30 kWh of electricity should give you enough hot water for roughly 45 people.  

countryhouse39

Thanks for your help! the good news is that we got an engineer to come and look at the pump  - the meter for there is faulty, so the readings I was getting from the flashing light on it are probably not correct. We are therefore going to replace that meter asap so we can know for sure how much the pump is using. He assured us that that meter wouldn't effect the main one though, so the main one should be correct. Reading the main electric meter we did use 37kwh of electricity yesterday though, which I do think is high for the time of year, so I'm not totally convinced that the readings from the other meter are entirely wrong - have attached the monitor to the main meter now and will go around the house turning things off and on to see what makes a difference (if anything). 
As a family of 5, (2 pre-school, 1 school age children) with both adults working at home 1 full time one part time (so associated computers etc) I'm not sure what level of electricity usage would be normal with the heating off. It was probably on for a short period yesterday evening as it was about 15deg during the day here, but not all that long as we have turned the heating requirements down.

matelodave

Some of these clamp on energy meters aren't ever so accurate especially when they are measuring a non resistive load and a heatpump can play havoc as it's got motors, pumps and inverters which can make it difficult.

When I go my heatpump I did a lot of  random button prodding to see what happened and TBH the first winter wasn't ever so successful, so I set up a spreadsheet listing all the controls and adjustments that were available in the menu's. I then added a column describing what they were for (coz some can be a bit obscure), I then added all the settings and readings so I had a base line to get back to if I mucked it all up. The system had been set up to default values which didn't suit us and in some cases kept it running at higher temps than we needed.

Then I started tweaking, one thing at a time, recording the new setting and recording the effect and giving it a couple of days to settle down. I also managed to record some of the inside and outside temperatures and the power consumption using a clamp on power monitor (mines an Efergy Engage which logs power in six second bits and you can get a graph and spreadsheet download. It's reasonably accurate, say within about 10% of the main meter).

It took a while but I've managed to optimise my system to suit our system and lifestyle.

I'd guess that your heatpump may have a sump heater as does our Daikin (it's 12 years old). Our uses 120watts so I've  started shutting the heatpump off completely now the weather is warmer and just turning it on for an hour or so  a day to heat the water.

120 watts doesn't sound a lot but it equates to  over 1000kwh a year which is around £300 a year now leccy is expensive. I wasn't too bothered when we were only pay 7-10p/kwh but it's now 29p

We dont need to keep the water above 45 degrees and it remains hot enough all day and night rather than the pump keep kicking on & off to maintain it's temp. The heatpump is now consuming about 1.6-2kwh a day to heat the tank. We are pretty frugal with hot water as we've got a low volume shower (about 6lpm) and we don't spend ages in there - I can do the full works in less than 2 minutes and washing up goes into the dishwasher.

Yours might also have circulating pumps running to maintain flow through the ground loops and the buffer tank, so it's worthwhile trying to identify what is using it and why.

In the end it really is a case of understanding how it operates, what happens when you tweak it then and optimising it to suit. It does take a fair bit of trial and error but it's definitely worth it

countryhouse39

I've been checking out our HW tank as I think this has to be where we are wasting electricity (albeit not as badly as I had worried about the last couple of days), and been looking at the manual for it. It is an ACV 'smart line e' tank  - and while it doesn't have a label on it, measuring the size of it it must be the SLE 300.

For the SLE300 - looking at the table attached, while it says 'total capacity' 293L, it says 'domestic water capacity' 200L  - I assume that means that we get max 200L of useable HW from a full tank as the other 93Ls down to it being a 'tank in tank' system? where the table says 'absorbed power' what is that? is there a way to ascertain from this info how much electricity it should be taking daily to heat our HW?

I note above @Reed_Richards you say that 100L of water is more than average 3 people would use - do you mean that an average person only uses 33.3L per day? That seems low to me? When I look up the average water usage for 1 shower its 35L for a 5min shower...?

In trying to work out our maximum daily usage I need to allow for 

2 x 5-8min showers in the morning for adults 
1 shower and 1 bath (relatively shallow - for small kids) in evening 
2 full loads of washing average a day 
2 dishwasher loads
handwashing etc 

Obviously some days not everyone showers and we don't have 2 loads of washing every day, but other days we have 4 and the eldest child decides to take ages in the shower...! 

QrizB

matelodave said:

Some of these clamp on energy meters aren't ever so accurate especially when they are measuring a non resistive load and a heatpump can play havoc as it's got motors, pumps and inverters which can make it difficult.

According to the OP (in this post a couple of pages back) it's one of those with a sensor that counts LED flashes:

It’s a monitor that is reading the meter in the pump room - it’s reading the red flashing light on the meter?

It should be as accurate as the meter is.

countryhouse39

QrizB said:

matelodave said:

Some of these clamp on energy meters aren't ever so accurate especially when they are measuring a non resistive load and a heatpump can play havoc as it's got motors, pumps and inverters which can make it difficult.

According to the OP (in this post a couple of pages back) it's one of those with a sensor that counts LED flashes:

It’s a monitor that is reading the meter in the pump room - it’s reading the red flashing light on the meter?

It should be as accurate as the meter is.

Engineer established yesterday evening that the flashing wasn't accurate - so the pump meter is going to be replaced, so I don't actually know how much energy it is using at the moment. Main electricity meter is fine though and is reading at us using approx 35kwh a day average for all our power in the last week or so.

matelodave

It's pretty easy to get through a lot of water, even when showering - I know mine consumes 6litres a minute because I've checked it by filling a bucket and timing how long it takes to fill. That means a two minute shower uses 12litres and ten minute shower will use 60 litres.

However there are lots of showers that can get through 10-15 litres a minute and a decent rain shower even more., you could easily empty your hot water tank. An Eco shower head might help if you are using a lot of hot water.

It's reckoned that a bath can use 60-80 litres, washing machines and dishwashers usually use cold water and heat themselves rather than using water from the hot tank.

Rinsing stuff and handwashing under a running tap can use a surprising amount of water and it's even worse if you run the tap until it's hot - ours wastes around a gallon of water before it gets hot and then leaves another gallon of lovely hot water sitting in the pipework to get get cold. If you must rinse stuff (including your hands, use the cold tap and save your hot water) Short draw-offs of hot water waste a lot of energy.

Our water is metered and weuse about 80cu.m of water a year = 220 litres a day but that does include an automatic garden watering system that runs between April and September which probably accounts for 20-30cum of that. We also have flow restrictors on the taps which limit them to around 3lpm, it takes a bit longer to fill the kettle but reduces waste.

countryhouse39

matelodave said:

It's pretty easy to get through a lot of water, even when showering - I know mine consumes 6litres a minute because I've checked it by filling a bucket and timing how long it takes to fill. That menas a two minute shower uses 12litres and ten minute shower will use 60 litres. However there are lots of showers that can use 10-15 litres a minute and a decent rain shower even more., you could easily empty your hot water tank.

It's reckoned that a bath can use 60-80 litres, washing machines and dishwashers usually use cold water and heat themselves rather than using water from the hot tank.

.Rinsing stuff and handwashing under a running tap can use a surprising amount of water and it's even worse if you run the tap until it's hot - ours wastes around a gallon of water before it gets hot and then leaves another gallon of lovely hot water sitting in the pipework to get get cold. If you must rinse stuff (including your hands, use the cold tap and save your hot water) Short draw-offs of hot water waste a lot of energy.

Interesting you say about the handwashing and the running the tap until its hot - it takes a long time for actual hot to reach our bathroom  - almost a minute running full blast before you get hot water from the hot water tap. There is a pump that is currently turned off that can make this quicker, its off to save energy but maybe that is a mistake, maybe it would be better on?

With your figures above then, that would mean that 3 showers, 1 bath would use approx 220L (50L a shower, 70L for bath) - so just over a tank full for us a day. I've used a formula I found online (Volume of tank x 4 x temperature rise / 3412 = Power required) and for that amount of water we'd use about 10.3kwh a day for water heating  - does that sound about right?