PDA

View Full Version : Confusion with two proposed systems







Goozelle
20-04-2012, 02:33 PM
We have moved to a house with a wet under floor system running off an electric boiler (thereís no gas in the area). After a scary electric bill I got two quotes for an ASHP but Iím finding comparing the two proposed systems quite difficult.

The first one is for a 14kw Ecodan to cover our heating and hot water requirements. We can have it with a Telford 200ltr twin coil un-vented cylinder or a Mitsubishi 200ltr unvented cylinder (single coil) which is a neatly package single unit.

The second proposal is for a 16kw Daitkin Altherma (variable speed compressor) split unit for the heating plus an Ecocent unvented cylinder with built in 800w heat pump for the hot water.

The idea of using separate systems for the heating and water we are told is more efficient and given the low pressure on our main will help boost pressure at the taps.

Iím having real problems deciding which is the right system Ė I like the simplicity of the Ecodan system but would the second proposal using two separate systems give us better pressure and be more economical?

Iím not a refrigeration engineer so donít have the technical knowledge but Iím hoping this forum can help me. Any advice greatly appreciated!

The Viking
20-04-2012, 03:44 PM
Do you buy a Ford or a Volkswagen when it comes to cars?

Both Daikin and Mitsubishi are reputable brands with good technical backup and support.
Both types of units will on paper be more than able to do what you are looking for, what it really comes down to is the installer.

Have you looked in to both companies background and experience?
Are they approved by the respective manufacturer?
Have they been on the courses?
Which sales guy had the flashiest/poshest car?

That is where the real difference between your two quotes lies...


However,
Single system or independent systems will not affect water pressures at the taps, it just can't.
The water will pass through a tank that got one or more heaters in it, whatever feed those heaters will have no affect on the flow of the water.

If water pressures are an issue, make sure all water pipework is "over" sized, 22mm minimum, all the way to just below the taps and not reduced to 15mm as soon as the pipework enters the building.
If it is really bad then booster pumps can be fitted but this will add to your running costs.

Oh, by the way,
The Mitsubishi Ecodan also use an inverter driven, variable speed, compressor....

.

:cool:

Goozelle
20-04-2012, 05:16 PM
Thank you for your help.

What I was really getting at was the difference between having one system for both heat and water, or having two separate systems for the heat and water.

Any pointers?

TiredGeek
20-04-2012, 08:32 PM
"The first one is for a 14kw Ecodan to cover our heating and hot water requirements. We can have it with a Telford 200ltr twin coil un-vented cylinder or a Mitsubishi 200ltr unvented cylinder (single coil) which is a neatly package single unit."

The Mitsi is a damn good unit.
Either of those cylinders seem fine, I'd opt for the Mitsi cylinder as it's bound to be compatible. The coil inside should have a 3sqm surface area for efficient heat transfer. No matter what cylinder you get, make sure of this.
The Mitsi is inverter driven also. Don't be put off simply because they didn't mention this bit. They can vary their output from full 14kw down to 5kw (I think I'm right there) as required by heating demand.
I particularly like the Mitsi unit as it's fully self contained, no indoor unit taking up extra space, only the DHW cylinder is indoors.

"The second proposal is for a 16kw Daitkin Altherma (variable speed compressor) split unit for the heating plus an Ecocent unvented cylinder with built in 800w heat pump for the hot water."

I don't know the Daikin unit so I won't comment on that. However, using an 800 watt heater to do your water is not cost effective. Assuming a COP of only 2 an ASHP will still be half the price to heat your water versus the in-tank heater which can only ever have a COP of 1. If you get COP of 3 or more then it's even more cost effective. Also, if it's all combined there's fewer seperate components to go wrong and easier to control.

Depending where you are cold temp operation may be an issue for you: the Mitsi 14kw unit will work down to -25'c, don't know how cold the Daikin will do, you'll need to check.
See what outputs they're capable of when it gets cold as well, make sure they don't fall back on to a "back up heater" which is essentially an immersion heater in your central heating system, costly to run.

With ASHP fitting is paramount. Be very very very careful who you employ, don't trust salesmen one iota. Take promises with a bucket full of salt.

If I could PM you I'd recommend someone to talk to, and someone to avoid, but I won't do it in open, sorry.

frank
20-04-2012, 09:19 PM
I'd opt for the Mitsi cylinder as it's bound to be compatible.
I'm not aware that Mitsi manufacture their own cylinder... I thought they had a tie up with Kingspan? But I'll bow down and be corrected.

I particularly like the Mitsi unit as it's fully self contained, no indoor unit taking up extra space, only the DHW cylinder is indoors.
Other manufacturers also do this type of system..it's called a Monobloc

"The second proposal is for a 16kw Daitkin Altherma (variable speed compressor) split unit for the heating plus an Ecocent unvented cylinder with built in 800w heat pump for the hot water."

The Daikin Altherma will do both heating and hot water without using a 3rd party cylinder. The DHW cylinders also have a built in electric booster heater.


Depending where you are cold temp operation may be an issue for you: the Mitsi 14kw unit will work down to -25'c, don't know how cold the Daikin will do, you'll need to check.
The Daikin will operate down to -20C

With ASHP fitting is paramount. Be very very very careful who you employ, don't trust salesmen one iota. Take promises with a bucket full of salt.
I have to agree.
Not to break the forum rules on advertising, but if you would like to send me a PM, I may be able to help

Jon Glanfield
21-04-2012, 08:40 AM
You will also want to have a think about your UFH pipe centres, manifolds and floor coverings. At design stage we spec 100mm centres and recommend tile/stone due to the high conductivity and large surface area of pipework which means flow temps can be lower.

You may find you have centres and floor coverings which require higher flow temps than are sensible on a standard low temp system, which is what you are being offered.

Your manifolds may also have blending valves that depending on your final selection would be better off removed to avoid flow rate issues.

A decent installer under the MCS standards will heat loss every room and then calculate the flow temp required to heat it based on the existing emitter. From this a correct decision can be made on whether you will be at the outer operating limits of a low temp (circa 50-55 degrees) which would not be advisable or efficient. There are high temp heat pumps available though if this transpires to be the case.

Mitsi have different packages available but the main difference is their control interface, the older unit is the FTC2 the newer is the FTC3, the latter is a better option because it is easier to operate, it is iterative, and uses internal and external temps to influence flow temp, (as opposed to just externals) but this is not that easy to interface with a multiple zoned UFH system.

Daikin's gear is good, but we have noticed that following the release of the latest MCS guidelines the software requires larger units than we were speccing previously (I won't bore you with the details now as to why).

The split is a good option because the heat exchange occurs inside the house, which is efficient and also obviates the need for glycol as per a monobloc. Glycol is expensive and protection levels have to be maintained, it also requires higher pumping pressures due to its consistency, that said we have installed plenty of systems with glycol without issue.

Both manufacturers will suggest you don't need a buffer, but we have found a buffer is essential for many reasons that have been done to death on here many times.

I don't know much about the Ecocent but I was talking to the distributors and they contend that it is a better option than running a low temp at max output to achieve hot water temps. There are a range of threads on Ecocents on the Navitron Forum to have a look at. I don't know the Telford, but we have been speccing Dimplex cylinders recently which are very good and quite cheap. OSO now have a cylinder with a combined buffer too if space is an issue.

Where in the UK are you?

Jon Glanfield
21-04-2012, 08:44 AM
Sorry also forgot to say that the jury is still out on whether inverters are the best way forward with Air to Water. Fixed speed, NIBE, Danfoss, Husky are simpler and more akin to traditional heat pump design we fit both, but prefer fixed speed because of their pedigree and lineage, often though they work out more expensive up front although the Husky is bucking this trend.

r.bartlett
21-04-2012, 12:03 PM
Sorry also forgot to say that the jury is still out on whether inverters are the best way forward with Air to Water. Fixed speed, NIBE, Danfoss, Husky are simpler and more akin to traditional heat pump design we fit both, but prefer fixed speed because of their pedigree and lineage, often though they work out more expensive up front although the Husky is bucking this trend.

had the exact conversation with a tech from a UK HP manufacturer. He was adamant that the 'need' for an inverter was driven not from efficiency but from the end user believing them to be more efficient. (baffle with BS)

Of course I remain firm ASHP's are all a load of ****e and wouldn't want one within a 100 yards of my 95% efficient gas combi.
I can only see two possible reasons for ASHP's

1 no gas
2 when combined with solar.

Without those gas beats HP's into the ground over a 365 day period and even the g.ment figures back this up

Jon Glanfield
21-04-2012, 01:41 PM
Well if the government and their "figures" say that it must be true!

Jon Glanfield
21-04-2012, 03:02 PM
Just another thought, depending on your budget, preferences and the quality of your existing cylinder, you could go bivalent, and use the existing electric boiler as the back-up for the ASHP and for the HW production.

You would then not be stressing a low temp unit by doing hot water, hot water production would not detract from the space heating (they occur independently in low temp ASHP set ups) and infrastructure costs would be lower. if you do find there is an issue with flow temps e.g. you need circa 50 degrees at minus 3, the boiler can do it and the HP can rest.

Can you get PV on the roof to offset costs?

r.bartlett
21-04-2012, 05:38 PM
Well if the government and their "figures" say that it must be true!

As the government is pushing hp's like mad and planning on phasing out domestic gas boilers I'd say it is true.. Only those with a vested interest would say otherwise..Your posts suggest that may include you?
Here's another example of energy savings not matching up to forecast
http://www.telegraph.co.uk/earth/greenpolitics/9197031/Green-measures-for-homes-save-less-on-fuel-bills-than-forecast.html

But hey there's a sale to be made so lets not worry about inconvienant truths

http://www.energysavingtrust.org.uk/Publications2/Generate-your-own-energy/Getting-warmer-a-field-trial-of-heat-pumps


At current electricity prices an air source heat pump
will provide a payback on the marginal installation
costs compared with direct electric heating in 10
years. This payback period increases to 16 and 31
years when compared with new oil and gas boilers,
respectively.

Jon Glanfield
21-04-2012, 06:38 PM
To be fair the telegraph report doesn't mention Heat Pumps at all and the EST field trials date back well before newer standards, better knowledge and even the first stage of the MCS existed, plus some of the units were self installed and on housing schemes by teams who were trained to install boilers not HP's.

We install Elster meters on our units and can therefore track performance daily if needs be, and then compare against manufacturer predictions, some of the systems are out performing the sims by up to 30% and these could have been on mains gas, given that the predictions were already marginally cheaper than mains gas the savings can be made in the right property with the right install.

Some of our customers acknowledge that the savings on gas are marginal and that payback is not necessarily a big selling point but they want to get away from future volatility concerns and spiralling costs.

We are of course a business, but we also install oil, gas and LPG and whilst the pure margin on the HP sale are very good, the job duration is longer and more involved which can erode the margin anyway. The older technologies are simple to install and quick to turn over so we genuinely try and match the solution to the project, budget and client preference, I spent half an hour with a bloke last week telling him to do nothing (he wanted to install GSHP in Victorian semi with a gas Rayburn range).

Naturally though some will over sell HP's as an ultimate panacea but many installs down the line we are only to well aware of their many and varied foibles and have the scars to prove it!

TiredGeek
21-04-2012, 09:10 PM
Naturally though some will over sell HP's as an ultimate panacea but many installs down the line we are only to well aware of their many and varied foibles and have the scars to prove it!

So am I, as you well know! ;)

I hadn't thought about the need for glycol, or lack thereof with a split system. For me it wouldn't be a good idea with outdoor temps hitting -25'c the indoor temps dropped to -15 after a few days, without glycol in the system we would have had split pipes and maybe even split rads.
Anyway, that systems gone now, good riddance :)


"Well if the government and their "figures" say that it must be true!"
ROFL. So true.


When the only realistic alternative to gas is oil or LPG, then the case for GSHP (if you can have one) or ASHP is much stronger. Yes, they're more money up front but the potential savings over oil is going to repay the investment many times over.
Many people seem to have this anti heat pump blinkered view, in the right circumstance heat pumps are correct, maybe not if you have access to mains natural gas, but when your nearest gas main is well over 100 miles away you don't have the choice. In a town environment the increased costs may not be so easily recovered, with oil at my house costing roughly £1.40 per hour (!) to run, an ASHP costing about a third of that will pay for itself quickly, plus no one can nick my electric as easily as heating oil ;)

Just make sure you can trust the fitters........

nec0310
09-06-2012, 09:11 AM
Hi Goozelle,

The idea of separating hot water and space heating is in principle a good idea. Look at the technical spec on the Ecocent tank reheat time. From cold, I think you will see around 6-7 hours!!
The Altherma will reheat a 300 litre tank from cold in around 1.5hours
Mitsi Ecodan and Daikin Altherma- both very good systems.
Altherma is more efficient. Mitsi Ecodan simplicity comes at a cost of efficiency - this is the down side of a packaged unit that is simplified to allow an easy install.

1) you will need gycol- efficiency loss
2) you will take water flow and return out of the house thus you will see a small temperature drop on your flow and return but this represents a large comparable efficiency loss

Altherma is designed as a split system transferring energy via refrigerant - there is a very strong efficiency reason why this system is designed this way.

Altherma needs to be installed by a company that understands split systems.

Hope this helps

nec0310
09-06-2012, 09:34 AM
Hi Jon,
Don't agree with the 'jury is still our on inverters'.
Daikin are just about to release next generation Altherma- COP >500% Seasonal COP >600%.
Daikin, Mitsi heavy, Mitsi electric, Panasonic, Hitachi,....big companies- have they got it wrong.
The compressor represents one of the major points of inefficiency within a heat pump system- any energy reduction in compressor energy results in significant improvements in energy efficiency.
European companies need to invest and catch up with the Japanese.
Turbo compressors from the Japanese will see scary COP's.

r.bartlett
09-06-2012, 10:10 AM
Hi Jon,
Don't agree with the 'jury is still our on inverters'.
Daikin are just about to release next generation Altherma- COP >500% Seasonal COP >600%.
Daikin, Mitsi heavy, Mitsi electric, Panasonic, Hitachi,....big companies- have they got it wrong.
The compressor represents one of the major points of inefficiency within a heat pump system- any energy reduction in compressor energy results in significant improvements in energy efficiency.
European companies need to invest and catch up with the Japanese.
Turbo compressors from the Japanese will see scary COP's.


Running at full load, a compressor delivers its best efficiency and outperform inverters. Inverter-based air conditioners have their strengths in environments where a partial load is common, as they are significantly more efficient than conventional air conditioners in those situations.

The argument is that why run an inverter on trickle when trying to heat a tank load of water. Running a std comp at full load is more efficient.
Now I have stated many times ASHP's should be considered a viable option when COP's hit 7+ (there is a theoretical max of 9 apparently) once that has been hit then they start to make real sense

Mini Turbocor may well provide the answer once costs have reduced sufficiently

nec0310
04-09-2012, 10:09 PM
The argument of a buffer is fine, as long as losses and extra pumps are considered in COP. EST report on heat pumps has shown many buffers are installed outside of a property insulation envelope.
Daikin altherma software requires the designer/installer to create a load(UFH/rads etc) to be matched to the inverter capacity range. If this is done, a std compressor cannot come close in COP.
Agree, COP improvements need to be made to get the real potential from heat pumps.

Bigfreeze
05-09-2012, 01:16 PM
Hi Jon,
Don't agree with the 'jury is still our on inverters'.
Daikin are just about to release next generation Altherma- COP >500% Seasonal COP >600%.
Daikin, Mitsi heavy, Mitsi electric, Panasonic, Hitachi,....big companies- have they got it wrong.
The compressor represents one of the major points of inefficiency within a heat pump system- any energy reduction in compressor energy results in significant improvements in energy efficiency.
European companies need to invest and catch up with the Japanese.
Turbo compressors from the Japanese will see scary COP's.

Even arguing about the various compressors as one of the major points of inefficiency in a heat pump system is like saying I could eat my soup faster if my fork was bigger.
You're looking at the wrong problem in the wrong place. This is not about compressors or expansion valves or anything else. Its about application and disparity between heat collected on side A and distributed on side B.

The FACT remains the heat pumps should not be used as direct replacements for oil and gas boilers and your big companies all ignore this fact because they care only about one thing, TURNOVER. Turnover of equipment and turnover of money. Nothing else. And air source heat pumps in the wrong application are even worse than ground source. If you can show me a ASHP with a SPF of 6+, I'll show you a heat pump thats installed in the tropics.

Its amazing the waffle the people will read on a pamphlet and swallow it whole.