Recommendations For An ASHP

[r.bartlett]

The latest inverter driven units by Mitsu and Daikin are where it is going. Don't buy a cheaper fixed rate compressor product; they are simply not as economical.

People are jumping on the inverter bandwagon into thinking that inverters with all their fancy twikerwee must save them money.

This is simply not the case as inverters are very inefficient at full speeds and during winter they will need to run at full speed for most of the time. Thus the supposed energy savings are nonexistent. Plus they often need 'top up heaters' in the immersion during cold weather further driving down energy efficiency

 

[ajstoneservices]

We've a customer trying to use solar to pre-heat the air supplied to his heat pump. I'm waiting with bated breath to hear the results.

 

[simond]

This is simply not the case as inverters are very inefficient at full speeds and during winter they will need to run at full speed for most of the time. Thus the supposed energy savings are nonexistent.

Can you provide any info as to how inefficeint they are?

Plus they often need 'top up heaters' in the immersion during cold weather further driving down energy efficiency

This is true but also the case with fixed rate compressor systems. Reason being it isn't economically sensible to scope a heat pump system that is suitable for full load on what is typically only a handful of days per year.

 

[doitall]

The latest inverter driven units by Mitsu and Daikin are where it is going. Don't buy a cheaper fixed rate compressor product; they are simply not as economical.

People are jumping on the inverter bandwagon into thinking that inverters with all their fancy twikerwee must save them money.

This is simply not the case as inverters are very inefficient at full speeds and during winter they will need to run at full speed for most of the time. Thus the supposed energy savings are nonexistent. Plus they often need 'top up heaters' in the immersion during cold weather further driving down energy efficiency

Have used hundreds of inverters for heavy load start-ups making them ideal for heat pumps.

 

[r.bartlett]

Can you provide any info as to how inefficeint they are?

All inverters must incur energy losses due to the conversion from AC to DC etc This is usually quietly forgotten about when bigging up inverters

This gives an outline of the losses. If you require more detailed explanation then I suggest you contact the manufacturers themselves

http://www.digitalscroll.com/sb300/portal/home/normal/17/show/0/8

This is true but also the case with fixed rate compressor systems. Reason being it isn't economically sensible to scope a heat pump system that is suitable for full load on what is typically only a handful of days per year.

A high spec single speed compressor will run at it's max efficiency when operating. If a tank of water requires heating up then there is a big load which one would presume requires heating quickly.

Plus the 'fudge' about a few day's per year isn't necessarily true when the tanks require to heat up to 63 deg's to prevent legionella -Daikins does this one a week btw. I understand they now offer a high temp version and I heard a CO2 one will 'do' 90 deg C but i also heard it's not as efficient at those higher temps..??

I am not necessarily knocking ASHP's per se , it's just as they stand they are not a complete package and require a step up to make them a worthwhile investment. Buy one by all means but beware of the snake oil salesman

Oh my local church is looking at a ground source and the vicar tells me the quotes are coming in around 250k..maybe it's time for me to see the light )

 

[Agile]

I appreciate that you may live on an undisclosed island with less than ideal fuel supplies.

However, be aware that you dont get something for nothing with heat pumps. They are fueled by electricity which costs about 4-5 times the cost of fosil fuels so they cost a fortune to install, have a very short guarantee and can be very expensive to repair.

Inverters are very efficient but thats not the point! An inverter allows the unit to work at a lower output when there is not a demand for their full output and that creates an improvement on overall efficiency.

Tony

 

[r.bartlett]

The latest inverter driven units by Mitsu and Daikin are where it is going. Don't buy a cheaper fixed rate compressor product; they are simply not as economical.

People are jumping on the inverter bandwagon into thinking that inverters with all their fancy twikerwee must save them money.

This is simply not the case as inverters are very inefficient at full speeds and during winter they will need to run at full speed for most of the time. Thus the supposed energy savings are nonexistent. Plus they often need 'top up heaters' in the immersion during cold weather further driving down energy efficiency

Have used hundreds of inverters for heavy load start-ups making them ideal for heat pumps.

A good soft start kit will do much the same for mush less. However you are missing the main crux -although i suspect you know this already

 

[calson]

Many thanks to you all for your replies, though whether i'm any the wiser i cannot be sure, as it got a bit techinical latterly.

Cheers.

 

[aa44]

Hi Calson. I live on Shetland and am going through the same decisions. For some reason, Nibe seem to be getting a bit of a foothold up here. I was speaking to the owner of a building firm here last week who installed a Dimplex unit a couple of miles up the road. He didn't go into details but told me that he didn't want to do another Dimplex one and that they are now doing Nibe. I haven't seen a Nibe ASHP in action but I was in a house a few weeks ago that had a Nibe exhaust air heat pump and the owner was raving about it.

Quite a lot of the new housing association properties both here and in Orkney have been fitted with exhaust air heat pumps and the tenants are reporting very low fuel bills. I spoke to Nibe about whether I could get awaywith one of these but they said that they would only cope with properties up to about 100 sq. metres. I am looking at about 200-250 square metres so I am going down the ASHP route, with the build starting (hopefully) next spring. I will be very interested to hear how you get on.

 

[aa44]

Calson - tried to reply to your message but it won't let me due to your inbox settings. I think that your inbox may be set to only allow messages from friends.

AA

 

[arty68]

I appreciate that you may live on an undisclosed island with less than ideal fuel supplies.

However, be aware that you dont get something for nothing with heat pumps. They are fueled by electricity which costs about 4-5 times the cost of fosil fuels so they cost a fortune to install, have a very short guarantee and can be very expensive to repair.


Tony

I'm not sure where you getting you electricity but its more like 3 times, check out http://www.nottenergy.com/energy-costs-comparison3 for sensible comparisons between fuel costs.

ASHP are not perfect however there not rubbish either, for most of the 90% year they will work well with good COPS of about 3-4 . for the 10% of days that are v.cold expect 1-2 so a back up heat source maybe required. Over the year including some backup heating I would estimate a COP of 2.5 is a good estimate.

This means compared to mains gas it's going to be a bit more expensive but not by much.

 

[aa44]

Good points Arty. It's also worth remembering that us island dwellers don't get that many really cold days. I used to live in Northumberland before I moved to Shetland and whilst, overall, Shetland is colder, Northumberland had many more extremely cold temperatures (e.g. -10) than you get on a much smaller island like Shetland or Lewis.

 

[calson]

In box sorted aa44.

Cheers.