ASHP efficiency in hot weather

[jack]

1 hour ago, SteamyTea said:

Even with optimisers you still get a hit that is out of proportion to the optimal.

 

Yes, but the hit is per panel not per string.

[SteamyTea]

2 hours ago, jack said:

Yes, but the hit is per panel not per string.

Well yes, that is what they are for.

But you can loose the output, or a high proportion of the output, for very little shading.

I installed a small, off grid, system.  When I went back to look at it a few weeks later because it 'had stopped charging the battery', I found a few dockleafs had shaded a corner.

What was really interesting though, was just how hot that module had got, way too hot to put your hand on, so over 70°C.

One of the problems of shading is that users are used to it.  This is mainly because the shading has always been there, so they do not know what the system could produce.

The upside is that we have a lot of overcast days in the UK, so on these sort of days, less, or no shadow is cast.

[H F]

On 03/08/2019 at 09:45, SteamyTea said:

Then there is start up current. There is a bit of a myth that they still draw a lot.

 

Can you please elaborate on what this means?

[H F]

On 03/08/2019 at 10:13, jack said:

Some brands have more expensive controllers available, which are allegedly easier to use

 

Were you referring to the control panel for the ASHP?

[SteamyTea]

9 hours ago, Home Farm said:

On 03/08/2019 at 09:45, SteamyTea said:

Then there is start up current. There is a bit of a myth that they still draw a lot.

 

Can you please elaborate on what this means?

'Instantaneous current is infinite'

When an inductive load is started, the current draw is often much greater than the running draw.

This can cause a voltage drop, which makes the current draw even higher.  Current leads voltage on an AC system.

To over come this 'soft start' devices are fitted to limit the initial current, this reduces the voltage drop.

This is why DNOs asks if you are fitting a heat pump, they may assume larger cables are needed, even though the fuse is the same rating.

 

V_peak = I_inR, where V_peak = √2(V)

 

E = CV²/2

 

https://sciencing.com/types-electrical-loads-8367034.html

 

Edited August 14, 2019 by SteamyTea

[jack]

10 hours ago, Home Farm said:

 

Were you referring to the control panel for the ASHP?

 

Yes.

 

For example, our Panasonic Aquarea came with a controller like this in the box:

 

 

It has an unlit LCD screen and is an utter pig to use. 

 

You can also buy more advanced controllers, like these (not sure which is available for current models):

 

Much easier to use, by all accounts.

 

There're also app-based controls available with many models, which adds another layer of flexibility(/potential problems!)

[ProDave]

I just jook the view that the supplied LG controller would sit there in the plant room for setting parameters etc and otherwise play no role in controlling the system.  I connected a conventional 3 channel central heating programmer to set the on and off times of heating and hot water, and conventional room thermostats.

 

So much simpler to use.

[SteamyTea]

5 minutes ago, ProDave said:

I just jook the view that the supplied LG controller would sit there in the plant room for setting parameters

Did you change any of those parameters?

[ProDave]

7 minutes ago, SteamyTea said:

Did you change any of those parameters?

Yes.

 

The way the hot water was set up was bonkers.  It was set to heat DHW only for half an hour at a time (I kept that) but then with a 1 hour wait before the next burst (I changed that to half an hour)

 

Then it was set to heat the DHW to 45 degrees with the HP then heat from there to 55 with the immersion heater.  I disabled the immersion heater phase and set it to heat to 48 degrees with the HP

 

I disabled the weekly heat to 60 degrees anti bacteria cycle after a discussion here suggested in our particular case that was unnecessary.

 

I also reduced the DHW hsteresis to 3 degrees, I forget what it was set to originally.

 

I set the maximum "water leaving" temperature in DHW mode to 55 degrees and in heating mode to 30 degrees. 

 

Enabling external thermostat control (the basis of external control via a programmer and room thermostats) required a DIP switch to be changed.

[SteamyTea]

21 minutes ago, ProDave said:

Yes.

Seems reasonable what you did.

The DHW heating cycling seems strange, but may have some benefits if the HP is already running to heat the house anyway.

Was it all fairly straightforward to set, or did it involve a manual, or 3.

[ProDave]

3 minutes ago, SteamyTea said:

Seems reasonable what you did.

The DHW heating cycling seems strange, but may have some benefits if the HP is already running to heat the house anyway.

Was it all fairly straightforward to set, or did it involve a manual, or 3.

I think the reason for the DHW only getting done in bursts is partly to reduce the time it is working hard in an effort to minimise the need for defrosting, and partly because when it is heating DHW it is not heating the house. So there is a presumed worry that the house might start to cool down if you stop the space heating for too long.  That would not apply to our house, I doubt we would notice until the next day that the heating was off.

 

It took some reading and re reading of the manual to really understand what some of the parameters actually do. the descriptions could be better.

[Hobbiniho]

1 hour ago, jack said:

 

 

Much easier to use, by all accounts.

 

There're also app-based controls available with many models, which adds another layer of flexibility(/potential problems!)

 

i have just had a panasonic system installed and have a controller that looks similar to this, it seems relatively easy to use although i have an old school rotary thermostat that does the call for heat. i am still at a stage where my system needs balanced and the plumber needs to change some settings, it is possible to have up to 6 heating programs and it looks quite simple to input the settings for that

[jack]

1 hour ago, Hobbiniho said:

i have just had a panasonic system installed and have a controller that looks similar to this, it seems relatively easy to use although i have an old school rotary thermostat that does the call for heat. i am still at a stage where my system needs balanced and the plumber needs to change some settings, it is possible to have up to 6 heating programs and it looks quite simple to input the settings for that

 

Thanks.

 

I think this is perhaps the newer version of the first version I posted above.

[H F]

On 14/08/2019 at 09:21, ProDave said:

I disabled the weekly heat to 60 degrees anti bacteria cycle after a discussion here suggested in our particular case that was unnecessary.

 

I’ve also done this. We have an iboost that takes us to 60C using ‘spare’ solar energy.

 

My question is whether Legionaries disease is an actual possibility and threat if the tank isn’t taken to 60C on a weekly basis.

[SteamyTea]

7 minutes ago, Home Farm said:

My question is whether Legionaries disease is an actual possibility and threat if the tank isn’t taken to 60C on a weekly basis.

To the best of my knowledge, there has never been a case in the domestic environment.

 

[Gone West]

58 minutes ago, Home Farm said:

My question is whether Legionaries disease is an actual possibility and threat if the tank isn’t taken to 60C on a weekly basis.

In an unvented system I can't see how the bugs could enter the pipework. We store our DHW at 45C and have for the last eighteen months. Hopefully my confidence won't be shattered.

[SteamyTea]

14 minutes ago, PeterStarck said:

We store our DHW at 45C and have for the last eighteen months

Have stored my DHW at 50°C in my old fashioned, vented system, with F&E tank in loft, for over a decade.

 

[Jeremy Harris]

1 hour ago, SteamyTea said:

To the best of my knowledge, there has never been a case in the domestic environment.

 

 

44 minutes ago, PeterStarck said:

In an unvented system I can't see how the bugs could enter the pipework. We store our DHW at 45C and have for the last eighteen months. Hopefully my confidence won't be shattered.

 

I've had the view that Legionnaires was a virtually mythical risk for UK hot water systems for years.  There's never, ever, been a case reported of someone being infected with Legionnaires from a domestic hot water system, and yet someone has decided that everyone should waste energy by heating up their DHW periodically in order to kill off bugs that almost certainly aren't there in the first place.

 

Legionnaires is primarily a problem with things like air conditioning, where the bugs can live and multiply in evaporative cooling systems and then get spread around and breathed in from fine water droplets that escape from the coolers.  Hot tubs and spas are another likely source.  Although there are guidelines for disinfection regimes for these, it seems they may not be easy things to keep clean and well-disinfected, perhaps due to the warm temperature they work at.

 

Looking at the statistics, it seems that the incidence of Legionnaires is around 240 to 250 people per year in the UK, with 50% of those being smokers, and most of the remainder having some form of long-term health problem (from the latest statistics about 75% of those who contracted Legionnaires had an underlying chronic health condition).  The peak months for the disease are between June and September, where the rate of infection is around four to five times greater than in winter.  This points strongly towards air conditioning and things like hot tubs being the most probable cause.

[SteamyTea]

There was a confirmed case cause by the airconditioning unit installed at the shopping centre in Aylesbury. Think it killed one person.

I used to go for a coffee there, but had to stand by the unserviced unit to have a fag.

Strange how it gets some people and not others.

The bacteria is often present in water, where it is quite benign, only when it is atomized into a mist, and at the right temperature, and then is breathed in by a susceptible person that it is a problems.

I don't think those conditions exist in a domestic shower.

[Jeremy Harris]

4 minutes ago, SteamyTea said:

Strange how it gets some people and not others.

 

 

Seems to primarily affect people who are already ill, or have compromised respiration, so are less able to fight the infection.  Around 75% of the ~250 cases a year are people who had a known underlying susceptibility to a lung infection.  Probably just chance that it was Legionnaires rather than one of the many other causes of pneumonia that caused their infection.  Overall, pneumonia kills around 28,000 people a year in the UK, so it's over 100 times more prevalent than Legionnaires.

[Stones]

On 30/07/2019 at 21:32, Home Farm said:

Are those figures annual?!

 

Not wanting to pry, but why are your heating requirements low? Houses in the uk require loads of heating.

 

£200 last year for heating (21.5C constant 24/7) with our ASHP - 155sqm footprint.  We are based in Orkney on a fairly exposed site.

[AliG]

I have been reading this thread with interest as a - I try to optimise my heating system now that we have been in for a year and b - I consider the heating system for my parents' place assuming that we get planning permission.

 

The discussion here has centred around heat pump, I have a gas boiler.

 

Looking ay my system I have the UVC thermostat set at around 57C and the boiler set in the low 60s. Ex hot water, the boiler could run in the 40s, the highest temperature on any of our UFH circuits is in the low 40s.

 

As I understand it, I need water returning to the boiler below 55C to get it into condensing mode. I should be OK on this.

 

But would there be further savings from making things cooler again.

 

My main question is heat losses, I have a hot water loop in the house as well as 4 UFH manifolds and the pool. Because the boiler needs to be set at 60C+ to heat the hot water, then I am ending up with lots of hot water circulating in lots of pipes at 60C. This is also causing some overheating. The loop will be in the high 50s as it is connected to the UVC, but other water will be at 60C+.

 

If I could reduce the UVC temp to the low 50s and the boiler temp to 55C then I should reduce heat losses across the whole system.

 

It seems from reading that this is an inherent advantage of a ASHP, they produce water at one temp for the DHW and one temp for the heating. A system boiler produces water at only one temperature.

 

Of course this goes into the legionella discussion that people are having. Am I brave enough to set the UVC to the low 50s. It sound like it is likely fine.

 

It seems that an alternative option is changing the UVC thermostat to some kind of timed thermostat that turns up to 60C once a day then 50C the rest of the time. Again this seems to be how ASHP based systems work but not system boiler based systems.

 

Anyway I have thus decided to change to an ASHP for my parents' house as I think it will work well for it. I won't get gas connected up at all which will create a large capital saving as well as saving about £75 a year in standing charges.

 

BTW wholesale energy prices have collapsed in the last few months. Some of the fixed price deals have started to fall in price. Outfoxthemarket who sell gas and electricity on a variable basis (but have a very bad record for service apparently) are undercutting other people massively at the moment. Looking at the drops in wholesale pricing though there seems to be room for more substantial price drops to come through even based on around 50% of the cost of gas and electricity being the wholesale cost.

 

[ProDave]

The way my ASHP (and I suspect most) work, is they don't use a conventional tank thermostat.  Instead they have a temperature probe that sits in a pocket.  So you can dial in any temperature and it will heat the water until the probe says it is that hot.

 

The tank thermostat is still used but only as an essential safety feature for the UVC.  I have it set to 65 degrees, and it the tank exceeds that it will close the 2 port valve to shut off heat input to the tank. 

[joth]

1 hour ago, AliG said:

I am ending up with lots of hot water circulating in lots of pipes at 60C. This is also causing some overheating.

 

How are you controlling the circulation pump? At the very least this should be on a timer so it just runs for a couple minutes in every 20 .  Ideally you can trigger this based on motion sensors near the rooms it supplies - but that's OTT if you don't already have the motion sensors.

Reducing the UVC supply temp will help reduce the loss  & overheating, although you then might need increase the circulation  pump freq a little bit more often to compensate.

 

[AliG]

Yes, the circulation pump is timed. It is set to run for 15 minutes in the morning, at lunch time, after school and before bed, but it has only been set on this schedule for the last week(see paragraph 3 for explanation).

 

Due to the pipes being insulated, the water seems to stay hot enough for a few hours. But I will be testing this new set up this week.

 

I just discovered last week, after a year of being in the house, that the hot water timer and circulation pump timer were switched around in the Heatmiser app. An extra control unit was added after the system was installed and no one told me that they switched around. So instead of the hot water being on all day and the pump 4 times a day, it was the other way around.

 

I only discovered this when I thought that I reduced the length of time the circulation pump ran for and my wife complained the hot water was not hot enough! In reality I was actually reducing the length of time the boiler ran for.

 

So I have around 70m of pipe sitting with hot water in it for the circulation pump, but this only runs 4 times a day.

 

I then have 5m of flow and 5m of return to the pool running through the media room ceiling, plus the around another 6m of each in the pool plant room. The pool heater calls for small amounts of heat constantly. I just checked the manual to see if I can reduce how often it cycles, but I cannot. This has been contributing to overheating in the media room along with heat from the AV gear. This is one reason I would like to run the boiler a little cooler. I have just insulated the plant room pipe work to hopefully reduce this cycling.

 

Then I have 4 UFH manifolds. The way the system has been set up, sometimes water is pumped to the manifolds even if the manifold pump itself is not running(I think this may have been exacerbated by the hot water pump running 16 hours a day until I noticed it was set up wrong). There is probably around 30m of flow and 30m of return to these manifolds. This is insulated, but what I noticed is that the manifolds themselves warm up slightly due to conduction of heat from the warm pipework. This heat in the pipework and manifolds is enough that the heating never needs to be on in the 4 rooms that they are in (one is the plant room). Annoyingly the WC is by far the coldest room in the house, if I had known about the manifolds heating up I could have put one in the cupboard next to it and not had to run the heating just for this one small area that is often cold).

 

To put it all into context, I reckon we now use around 90kWh a day of gas for hot water and pool heating. I think it was around 110kWh before I started optimising it. Around 50-60kWh is for the pool, around 15kWh is for DHW and around 20-25kWh is pipe losses. So that is around £200-250 a year in pipe losses.

 

The one useful piece of advice anyone might take from this is that if you have an area in your house that will obviously be cooler than other areas, e.g. north facing, lots of outside walls/glass then try and put your UFH manifold or anything else that produces excess heat here. Use your heat losses to run your heating less rather than overheat rooms that don't need heating.

 

As we approach winter again I will start to try and make sure all the last air leaks are blocked up. I think we used around 500kWh of gas on the coldest day of the year last year, so close to 400kWh for heating. So improving on heat loss will make a bigger difference. There are already some issues that have been sorted since last winter, e.g the flue for the kitchen fire was not sealed. Also we did not have mastic around all the windows on the outside and inside until March this year. This made quite a difference to air leakage as well as noise leakage.

 

It will be interesting to see if the fixes applied since last winter make a big difference to heat requirements this winter. The house uses a lot more heat than modelled, although still around half what our last house used per square metre. I suspect it will only be modestly less this winter.

 

 

 

 

 

 

Edited August 16, 2019 by AliG