LPG boiler vs heat pump set up « Alternative Technology Assn Forums

Alternative Technology Assn Forums » Sustainable Building

LPG boiler vs heat pump set up

(19 posts) (6 voices)

Started 8 years ago by darrynm
Latest reply from VioletAngelo

Tags:

darrynm
Member

We have an existing radiator system in our house but nothing to heat it right now (we removed the old cooker). We have 12 radiators and approximately 18-20 KW of heat output @ 60 degrees.

Looking to install a heat pump system that would give us from 9-13 KW heat output and cost $10,000 to $13,000 installed. So it's a big up front install cost but if we ran this on an off peak 2 tariff (up to 18 hours a day) and with a COP ~3-4 our annual heating cost might be as low as $400.

Compare this to an LPG boiler either 18 KW or 30 KW and installed would be around $6500-8000. Ongoing costs per year would be around $600-800 depending on LPG prices for the same heating as above. The pros of the boiler is it's 'simple' technology (=easy to repair etc), known to be reliable, is powerful at 18 KW, and has a fast response time.

Over ten years the heat pump system just wins out on cost but the big question for me is: does a heat pump hydronic system really cut it?! Every local plumber I talk to reckons they dont run as well as the theoretical COP and can be disappointing + cost a lot to have installed. The argument is good - heat pumps are newer technology and more complex, but maybe they've only experienced the poorer performing domestic hot water heat pumps vs units designed for hydronic heating.

Costs aside, can anyone highly recommend a heat pump hydronic system? Do they deliver on the theoretical outputs and heat the radiators well?

Posted Wednesday 19 Jun 2013 @ 11:48:05 am from IP #
pulpo
Member

Have a look at Sanden Heat Pumps.

They say should get your 9kw (with two) output, down to 0 degrees with 2 kw in put.

The enter shop has sold many this way.

Do a heat load calculation for your house, see link below.

http://www.solarsatisfaction.com.au/Technical.html

For heat load calcs, the walls only look at external wall area.

Your LPG costs seem too low.

Not sure what the heat output of the boiler would be but if looking at 10 kwh.

That would be around 1.5 litres of LPG.

At a $1.70 a litre would cost around $2.55.

10 Kwh output with a sanden heat pump is 2.22 kwh input.

In rural nsw at $0.35kwh equals $0.777

Which is 70% cheaper than LPG.

I know a few with LPG boilers and rarely use them because so expensive.

Good luck

With your heating

Pulpo

Posted Monday 24 Jun 2013 @ 3:37:35 am from IP #
darrynm
Member

Thanks Pulpo - I was guesstimating LPG cost per year but since that post and more info I agree it will be much higher running cost, maybe $1200-1400 a year even if we can get it at a bulk (=tanker fill on site) price for around $1 a litre (not including tank hire).

It's the upfront install cost of the heat pump systems that hit the budget pretty hard and even then you dont get a really powerful system eg 9kw vs 18-30kw boilers. Over ten years it evens out but I worry we will be asking too much of the heat pumps and the overall cost might blow out with maintainence & any repairs.

Posted Monday 24 Jun 2013 @ 4:05:25 am from IP #
darrynm
Member

Ok some more calculations: LPG cost via bulk delivery and filled on site (eg 190 or 210 kg tank) is $1 a litre. 1 litre LPG = 26 MJ = 6.5 KW/hrs (if boiler at 90% efficiency). So 1 kw/hr costs 15.1 cents.

Compare with mains gas around 10 cents per kw/hr (includes supply cost & is based on an old bill so might be different).

Heat pump eg Sanden x 2 working at an average COP of 4 on NSW peak tariff (including supply charges) = 30 cents / 4 = 7.5 cents per kw/hr.

So the price per kw/hr shows LPG would be double that of the heat pump. But a typical gas boiler installation might be around $4000 cf heat pump system of say 9 KW at closer to $11,000, so a difference of $7000 installed.

If we assume 10,000 Kw/hrs heating required this means running costs LPG per year are $1500 + $250 tank rental = $1750 vs $750 for the heat pump = $1000 difference so with the $7000 install difference it would take 7 years to even out the higher installation of the heat pump.

Posted Tuesday 25 Jun 2013 @ 11:33:31 pm from IP #
pulpo
Member

Your calculations I dont think are correct.

26 MJ is closer to 7kwh.

I'm paying $145 to swap a 45kg (90L) cylinder so a good deal if they come and fill a cylinder for $1.00 a litre.

Pulpo

Posted Wednesday 26 Jun 2013 @ 12:44:08 am from IP #
darrynm
Member

Oops yes 26 MJ = 7.2 kw/hrs or 6.5 kw/hr if boiler at 90%. I'll edit the figure above. But the price per kw/hr is still 15.1 cents if LPG is $1 a litre.

I have two quotes for $1 per litre delivery each week if required and they fill on site. Rental of their bottle (usually 190kg or 210kg) is around $250 a year.

The same companies delivering a 45kg bottle to swap and the cost per litre works out $1.36 so this is 20.9 cents per kw/hr.... which would really blow out the running costs.

Posted Wednesday 26 Jun 2013 @ 12:54:08 am from IP #
Bushwalker
Member

There are a lot of heatpumps in use (your fridge, for instance) and generally their reliability is quite high. It is true that a couple of brands of heatpump domestic hot water have stained the technology with their lousy designs and production standards, but I would not let that sour your decision making process. (you're not installing a domestic hot water service)

I'd be finding some referrals. If none appear here, approach the heatpump suppliers and ask, you should be able to get a look at a working installation and query the owners.

Not being familiar with hydronic systems in general, I'm making a few assumptions here as to why a gas system seems better performing: might be because they have a small tank and a high MJ output compared to the heatpump. I think a well designed heatpump system should be able to get around that with a decent sized storage tank.

The other worthwhile thing to explore would be solar boosting the heatpump using an economical solar array (runonsun?) attached to the storage tank.

Heatpump efficiency is generally quoted at their best efficiency and at a certain outside temperature, and they definitely perform below that efficiency in less than ideal conditions but they will always be more efficient than gas or electric resistance IMO. If you plan on staying in this place for a while, I'd be surprised if the sums don't point to the heatpump solution despite it's higher capital cost.

If you search here for hydronic, you should turn up some posts by TonyT who is running a small hydronic system very economically on (shock!) a Siddons domestic hot water system.

BW

Posted Wednesday 26 Jun 2013 @ 3:59:09 am from IP #
darrynm
Member

The gas boilers I have been looking at have a small 10 litre tank so likely can be heated very quickly with the boiler at max output 18 or 30 KW and then this is pumped direct to the radiators for fairly instant heat. And no storage tank = no heat loss.

From what I understand of the heat pump systems it would be a slower heat depending on the storage tank temperature and system size eg 13KW or 18KW if you use 2-3 Sanden units piggy backed together.

Yes I know about Tony's system and ideas and have PM'd him a few times - he's been very helpful I think it's a great way to go for a smaller floor space given he uses the heat pump on the overnight off peak tariff - but I'm unsure whether a larger system would qualify to be an approved off peak appliance (I'm clarifying this now with my energy supplier!). I think they're meant to supply domestic hot water systems....maybe not central heating systems?

For heating a larger home I am finding it difficult to look past the power, low-ish install cost, and simplicity of the boilers. I'd much rather use solar based system for environmental reasons but it's either very expensive or doesnt quite cut it!

And another idea - if the heat pumps work out at around 7.5 cents per KW (30 cents peak tariff / COP 4) then it's not really much better than paying 9 cents for off peak running 8 hours overnight?! Maybe you need a dual power supply: run one heat pump unit on the off peak tariff and another on peak to even out the running cost but allow it to be used all day.

Posted Thursday 27 Jun 2013 @ 11:36:38 pm from IP #
Bushwalker
Member

darrynm said:
And another idea - if the heat pumps work out at around 7.5 cents per KW (30 cents peak tariff / COP 4) then it's not really much better than paying 9 cents for off peak running 8 hours overnight?! Maybe you need a dual power supply: run one heat pump unit on the off peak tariff and another on peak to even out the running cost but allow it to be used all day.

Except that overnight rate has also to be divided by the COP. Apples with apples. I don't think we can get 9 cents any more, ours is 12.8c/kWh, so 3.2c per KW of heat out of the heatpump (in ideal conditions).

2-3 Sanden units piggy backed together sounds like a kludge. At that output capacity, surely there is a specific unit designed for the task. Asking for maintenance nightmares IMO, 3 compressors, 3 sets of control equipment, 3 tanks?

I'd honestly be surprised if the LPG setup worked out cheaper over time than the heatpump system even on day rate. Gas systems have always been relatively cheap installations, but the running costs are higher, especially on LPG.

BW

Posted Friday 28 Jun 2013 @ 7:50:25 am from IP #
darrynm
Member

Yes the maintainence & servicing issue is a big one - trying to find a local plumber to install a heat pump system has been difficult, but you could pick one of many for installing and fixing a boiler set up.

The problem with using a domestic heat pump system overnight is you only get around 300 litres of water at 60 degrees = 14 kw/hrs if the temp drops to 20 using raditors. Not a lot of heat so you need a bigger tank eg 500 litres but then you cant use a domestic system.....which means you go to more expensive hydronic heat pump options AND I question whether these can be used on an off peak rate.

For underfloor heating needing a lower operating temp 30-40 degrees (like TonyT is doing) a domestic unit with 300 litres would be fine for a full day. But with radiators requiring 60 degrees it only gives you a few hours heat.

And the domestic units dont come ready for solar so you cant add in a boost option during the day. I think it leaves you needing to use a stand alone tank eg 500 litres with 1-2 heat exchange coils (1 for solar, 1 for the radiators) and then boost with an electric element. Overnight boost of 500 litres to 60 degrees gives you 23.3 kw/hrs (enough for a morning warm up) and then the solar ET can hopefully kick in around 10am to carry you through the day & afternoon. I imagine this set up would lose heat late afternoon / early evening but at least the house would be warm already & we have a fire.

Unless someone knows a way to add a domestic heat pump unit to this kind of set up? With another coil perhaps? I have tried working it out but I cant see how it can work as they operate under pressure and have a 'water used, new cold water in, heat up, stop heating' vs a hydronic heat pump which has it's own pump and circulates the same water around and around.

Is there a way to recirculate water through a domestic heat pump? That way you could use one to boost during the day or even overnight and maybe on the off peak rate.

Posted Saturday 29 Jun 2013 @ 12:29:53 am from IP #
Bushwalker
Member

darrynm said:
Yes the maintainence & servicing issue is a big one - trying to find a local plumber to install a heat pump system has been difficult, but you could pick one of many for installing and fixing a boiler set up.

The problem with using a domestic heat pump system overnight is you only get around 300 litres of water at 60 degrees = 14 kw/hrs if the temp drops to 20 using raditors. Not a lot of heat so you need a bigger tank eg 500 litres but then you cant use a domestic system.....which means you go to more expensive hydronic heat pump options AND I question whether these can be used on an off peak rate.

For underfloor heating needing a lower operating temp 30-40 degrees (like TonyT is doing) a domestic unit with 300 litres would be fine for a full day. But with radiators requiring 60 degrees it only gives you a few hours heat.

From what you have told us here, you have a home with an existing substantial hydronic system. "We have 12 radiators and approximately 18-20 KW of heat output @ 60 degrees."

Have you approached any hydronic installers to quote on a suitable heatpump system to power your heating system? It strikes me that asking a plumber to assess the heating requirements, installation and control of a hydronic heating system based on a heatpump is stretching their field of expertise, most would run a mile. A quick google search turns up a few possibilities:

http://devi.rtrk.com.au/?scid=105420&kw=1353574:21956&pub_cr_id=8878829240

http://www.comfortheat.com.au/HydronicHeating/DIYHYDRONIC.aspx

http://solarhydronics.com.au/co2-heat-pumps/

http://www.skylineenergy.com.au/water_heaters_radiator_domestic.php

9kW Heatpump, good for 315m2 heating with panel radiators:
http://www.skylineenergy.com.au/Heat_Pump_Hydronics_SX-35.php

From that last one:

We do not recommend using multiple domestic-type storage tank heat-pumps for hydronics, as these work best with fairly static water - hydronics requires continuous water flow, better suited to co-axial heat exchangers which are more efficient

HTH,

BW

Posted Saturday 29 Jun 2013 @ 11:57:23 am from IP #
julie
Member

Darryn

I'm looking at heat pumps and gas boilers for an in slab hydronic sized for a 200 sqm build-central vic. I have quotes for 2HPs and waiting for gas boiler quote.
For the gas system they are suggesting buying the tanks- 2 to 3 K- so you can shop around for better price per litre. He has a customer that , last year ,could get it for 60 to 80cpl-unconfirmed. I'm sure the complete install quote will be well under that for the HP quotes but I'm hoping to go with a HP.

The HPs are: Daikin Altherma- inverter type
SX20 -has a buffer tank- from Skyline Energy -their website is very informative

The quotes for both of these are very similar and although all inclusive - pipes ,electronic controls,HPs ,tanks and probably the steak knives- $ 26K is a lot!
Julie

Posted Sunday 30 Jun 2013 @ 3:59:48 am from IP #
darrynm
Member

Hi Julie,

I did hear you can get good pricing if you shop around for the LPG - a plumber thought he could get it as low as 80 cents per litre. At say 80 cents a litre it works out to be 12 cents per KW/hr so adjusts running costs down by 20% and this would make the boiler option far cheaper for us. But in your case you've got the tank cost you mentioned! And then factor in LPG price rises too? Id' wager LPG will rise more than electricity in the next ten years.

We had an option for the Daikin Altherma 16 KW but the person quoting didnt think it would be powerful enough as we needed around 20 KW for our radiators (if all going at once). The total worked out to be around $13K installed (but without any radiators as we have them existing). Cost per year on 10,000 KW/hrs would be around $750 if COP = 4. Cf LPG per year if $1 a litre = $1718. So you save $1000 a year vs LPG but we would spend $9000 more upfront to install.

Skyline I have been in contact with and found them very helpful. I think they said the SX-20 for us too. But it's the hassle of getting someone local to install - even a plumber I phoned a week ago in Canberra and said he'd installed their gear before hasnt sent me a quote. It's quite frustrating getting someone local - what will happen if we need it serviced?! Lots of companies it seems in VIC and SA but not many in NSW.

At the end of the day each option for us on my calculations works out to be around $5000 difference over ten years when adding up install + yearly costs - for a new build or if you have plenty of $ this might not be a deal breaking amount! So it might be better to select on the intangibles like reliability, environmental impact, and warranty / the availability of servicing / parts etc.

My current plan is to get a large tank around 500 litres - have it made with 2-3 coils and a boost electric element. Heat it up overnight on off peak rates 9 cents per kw so 500 litres = 23 kw/hrs = 50% of our annual requirement.

Then get 30 or 60 evacuated tubes to boost during the day via the first coil and hopefully get another 20-30% of our heat (for free!).

Then for the 20-30% we could boost via a second element in the tank on peak rates 27 cents per kw, or with the second coil connect to our fire or just get a heat pump say the SX-20 to get us through long cloudy periods.

All up it might $300-4500 for the install of the tank & ET set up and then around $600 a year running costs. Adding a heat pump would push the price up but would make the system 'cloud proof'!

Posted Sunday 30 Jun 2013 @ 6:49:17 am from IP #
TonyT
Member

darrynm

If daily heat needed is 50kWh, using night rate electricity at 10cent/kWh for off-peak electric resistance heating the cost is $5/day.

If heating is needed for 200 days/year the cost is 200 x 5 is $1,000/year.

Using a heat pump with COP 4.0 the annual cost for heat of 50kWh/day is $1000/4 is $250/year, a saving of $750/y.

For investment to be paid back in 5 yrs, could invest 5 x $750 is $3750.

Compare cost to heat using LPG at ? 20cent/kWh is ? $2000/year.

Will you ever need your existing radiators to output their full 20kW capacity at the same time ?
Radiator performance specs are at
http://www.ata.org.au/forums/topic/635#post-25624

What is the max kW of heat input that you are using with however you are heating now, during this winter ?

Posted Tuesday 2 Jul 2013 @ 12:09:46 am from IP #
Bushwalker
Member

How big a tank would you need to usefully store that much heat on night rate for such a heating system?

Posted Tuesday 2 Jul 2013 @ 7:10:09 am from IP #
darrynm
Member

Bushwalker said:
From what you have told us here, you have a home with an existing substantial hydronic system. "We have 12 radiators and approximately 18-20 KW of heat output @ 60 degrees."

Have you approached any hydronic installers to quote on a suitable heatpump system to power your heating system? It strikes me that asking a plumber to assess the heating requirements, installation and control of a hydronic heating system based on a heatpump is stretching their field of expertise, most would run a mile.

Yes I have two quotes for supply only and one more coming. The equipment required to run our whole radiator system requires a hefty up front cost - I'm sure it's all worth it but it does take up to ten years to get the return back compared the cheaper install options. The chance of repairs etc during this time is another possible cost. And as I mentioned another issue is getting a local installer able to do it - like you said most run a mile.

I was also concerned we couldnt use off peak rates for a central heating system - had a phone call today from our power company and they have given the ok for using it off peak 2 rate - 13 cents per kw - running 10pm to 4pm - so we only lose power from 4pm to 10pm each day. With a large enough tank we should get through that time period just fine.

13 cents / COP 4 = 3.25 cents per kw and I cant imagine getting a running cost any lower than that.

As such I'll go back to looking at adding a hydronic heat pump to the set up - I'd still like to have a solar ET option and a large tank 500 litres is useful for storage.

Posted Tuesday 2 Jul 2013 @ 10:49:05 am from IP #
darrynm
Member

TonyT said:

Will you ever need your existing radiators to output their full 20kW capacity at the same time ?

No - we have a few rooms that arent used during winter that are included in the 18-20 KW total. Our main living areas & bedrooms & bath total around 10 KW of radiators.

What is the max kW of heat input that you are using with however you are heating now, during this winter ?

We run a few small heaters plus a fire. So maybe 6-8 KW in total and this is adequate....but only just and paying the full peak rate for power is expensive.

Posted Tuesday 2 Jul 2013 @ 10:54:31 am from IP #
darrynm
Member

Bushwalker said:
How big a tank would you need to usefully store that much heat on night rate for such a heating system?

A 500 litre tank at say 70 degrees dropping to 30 degrees releases 23.3 kw/hrs. If we are aiming for 50 kw/hrs a day a tank heated overnight is only providing half and would run until around midday if started up at say 6am.

Then the solar tubes could kick in from around 9/10am providing another maybe 5-8 kw/hrs per 30 tubes per day (so not a lot). But this would be more heat generated in the shoulder months.

Then in the evening we'd need to have the fire going, or boost the tank on peak rate, or this is when a hydronic heat pump could be used to keep things running.

Posted Tuesday 2 Jul 2013 @ 12:08:02 pm from IP #
VioletAngelo
Member

Hi everyone, just wondering 3 tanks (315Lt Sanden) would this be enough to service 15 apartment?
11 2 bedroom 3 1 bedroom?
At the moment we have 3 boilers 260Lt capacity servicing our apartments?
Any suggestion?
Any other apartments that have changed to heat pumps and any feedback thanks.

Posted Thursday 29 Oct 2015 @ 4:20:10 am from IP #

RSS feed for this topic