Underfloor heat pump heating

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SumnerBoy

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#1396545 29-Sep-2015 12:21

re. HWC - no, my understanding is typically those air-to-water heat pumps are not designed to run very hot - mine only heats up the water to about 35 degrees. This isn't enough to heat the HWC without a big heat exchanger. Although I have heard of systems that advertise this feature - just not convinced how effective it would be. Added to that, I installed solar evacuated tubes which handle my HWC, along with nighly electric boosting when required.

re. Garage - no pipes run to the garage, but I ensure I insulated between the garage slab and the house (attached garage) to try and stop heat seepage.

timtait

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#1396582 29-Sep-2015 13:19

Happy to answer any questions, I installed my underfloor system myself and just got a plummer to hook up the heat pump.

My old man's a plumber so I was wondering if I this was an option. Do you know what this roughly worked out cost wise? Most quotes I've had to get it installed are around 25K.

SumnerBoy

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#1396586 29-Sep-2015 13:24

I got a decent NZ-made heat pump from Hot Water Heat Pumps which cost $7-8K (in 2011), then the pipes and manifold were pretty cheap - I think a couple of hundred $ per 100m length of pipe (one length per zone). The manifold was under a grand - I would go for quality tho - I went cheap and spend my life worrying I am going to wake up with an inch of water inside!

From memory my entire system cost about 12K all up - not including my time to run the pipes pre-pour.

billgates

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#1396595 29-Sep-2015 13:33

I have had 2 quotes come back to me recently for UFH. One from Leap and other from John Guest. It's a 450 square meter double storey house. Leap is $30,500 and John Guest is $24,000 for both floors. I am still going through the fine details of both but JG looks good considering it's sold overseas as well. Price is for a Bosch 18kW gas boiler unit though as heat source. Heat Pump + small buffer tank is extra $5k + GST

Do whatever you want to do man.

SumnerBoy

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#1396601 29-Sep-2015 13:39

FYI - this is the heatpump I have (http://www.waterheating.co.nz/Products/Residential/Underfloor+Heating/7GUb9-1/). It is 9kW and has an onboard circulating pump and buffer tank which means you just hook the flow/return pipes to your underfloor manifold and turn it on. My house is 260sqm, two story (including a 48sqm garage which I don't heat). The ground floor foot print is about 150sqm (excl. garage) and this 9kW unit works great - remembering I only run it from 9pm till 7am. In the middle of winter it runs full time during that period, but for example at the moment it turns on at 9pm and usually flicks off again about 2-3am.

MikeAqua

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#1396602 29-Sep-2015 13:39

Have you considered a ground to water heat pump?

Efficient and the capital outlay maybe justified by the longer heating season in Dunedin.

Mike

SumnerBoy

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#1396606 29-Sep-2015 13:41

Yep - geothermal is ideal if you have the capital up front, and the land area to install it. Wish I could have done this, looked at it seriously but it was prohibitively expensive and I just didn't have the room on my site.

billgates

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#1396607 29-Sep-2015 13:41

SumnerBoy: FYI - this is the heatpump I have (http://www.waterheating.co.nz/Products/Residential/Underfloor+Heating/7GUb9-1/). It is 9kW and has an onboard circulating pump and buffer tank which means you just hook the flow/return pipes to your underfloor manifold and turn it on. My house is 260sqm, two story (including a 48sqm garage which I don't heat). The ground floor foot print is about 150sqm (excl. garage) and this 9kW unit works great - remembering I only run it from 9pm till 7am. In the middle of winter it runs full time during that period, but for example at the moment it turns on at 9pm and usually flicks off again about 2-3am.

Do you have UFH on the first floor of your house? If so, does it works well and if not, does first floor still stays warm from rising heat from ground floor?

Do whatever you want to do man.

SumnerBoy

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#1396612 29-Sep-2015 13:46

No UFH on the first floor. We only have two bedrooms up there and they typically sit at a couple of degrees below the ground floor. So between 18-20 degrees. Again, insulation is the biggest factor, if you can trap as much of that warm air inside it should retain the heat pretty well. If I had a living area upstairs I might have needed some secondary heating tho. But in the 4 yrs we have been living here there has never been a heater plugged in upstairs.

timtait

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#1396614 29-Sep-2015 13:53

MikeAqua: Have you considered a ground to water heat pump?

Efficient and the capital outlay maybe justified by the longer heating season in Dunedin.

I'd love to go geothermal but we don't have the land area on site

timtait

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#1396617 29-Sep-2015 14:01

SumnerBoy: FYI - this is the heatpump I have (http://www.waterheating.co.nz/Products/Residential/Underfloor+Heating/7GUb9-1/). It is 9kW and has an onboard circulating pump and buffer tank which means you just hook the flow/return pipes to your underfloor manifold and turn it on. My house is 260sqm, two story (including a 48sqm garage which I don't heat). The ground floor foot print is about 150sqm (excl. garage) and this 9kW unit works great - remembering I only run it from 9pm till 7am. In the middle of winter it runs full time during that period, but for example at the moment it turns on at 9pm and usually flicks off again about 2-3am.

Cool, thanks that's really good to know. We're looking at heating ~170sqm, I might give those guys a call

fwiw here's the layout -

bfginger

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#1396852 29-Sep-2015 21:07

The New Zealand building code has weak insulation and window performance requirements so a standard build can be costly to centrally heat. A build in the same climate overseas may have over double the insulation.

The concrete slab should have a thermal break and perimeter insulation along the edge. 80% of concrete heat loss is from the edge.

Windows and doors should be thermally broken if they're aluminium. The standard R2.2 and R3.2 insulation in the walls and ceiling is too low but it's normal for over 50% of heat loss in a new house to be through the windows because of poor quality products an excessive glass area.

Many people have had problems with ducted heat pumps because they are difficult to install and as so few are installed in New Zealand the installers may not know what they're doing.

Many underfloor hydronic systems in New Zealand have been installed directly into the concrete slab so the slab itself must be heated. There are systems where you can have the pipes installed over the slab inside a plastic interlayer that goes over the concrete and under the floor. As that isn't directly heating the concrete it may be more responsive. Central heating can be set up to have different parts of the house as separate zones.

The Hot Water Heat Pumps company does a range that can supply hot water for both central heating and general usage. The Daikin Altherma can be set up to provide the house's hot water and summer cooling too. The Altherma is probably more efficient but it should have a higher price tag.

Dunedin doesn't have very cold temperatures but they won't work as efficiently at 0 degrees as at 7.

Hydronic heat pumps can be set up to work with radiator central heating too if you don't want underfloor heating. Underfloor provides the most even heating as heat rises.

Ground source heat pumps are more suitable in places with geothermally warmed earth or large seasonal differences. As the underground temperature stays stable across the year it allows a heat pump to work well when the air is too cold for air source heat pumps to work efficiently. They may make sense in places like parts of Central Otago and Rotorua but I doubt the economics add up for them in any coastal area.

Aredwood

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#1398356 2-Oct-2015 00:32

According to the tech specs page on the Altherma site it has a 3kW electric bosser element fitted. Also it doesn't quote what water temps have been used when calculating the COP. As all you need to do when testing is to leave a hot tap running full bore so that the unit can't build up any temp in it's cylinder. This means that the incoming water temp to the condenser/heat exchanger is only around 15deg So good COP is easy. Now try feeding in 50deg water and have the altherma heat to 55deg Very much doubt it will still get it's claimed COP. (this situation will happen whenever the cylinder just needs "topping up"). And since the max temp it can produce is 55. (which it says on the specs page) The electric element will be needed to get to 60deg for legionella control.

So I doubt that a hot water heatpump used to supply domestic hot water would work well enough where you are. Especially as you can just get a big electric cylinder and heat it using night rate power. Any efficiency savings will be lost from having to pay daytime power rates to run a domestic hot water heatpump during the day. As lower temps at night mean lower efficiency.

A hot water heatpump for just underfloor should be fine though. But still check those lines company policies.

timtait

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#1398391 2-Oct-2015 01:34

Also the quotes I've had so far put the hot water heating option at around $4.5K including the cylinder. I'm thinking I'll just go gas powered water, instant on demand hot water.

SumnerBoy

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#1398447 2-Oct-2015 08:38

Interesting point about running the underfloor heat pump during the day/night and how it would affect COP. My theory has always been to run it only from 9pm - 7am, and thus take advantage of the cheap night rates (almost 1/3 of day rates). My assumption is that that is a far better return than the improvement in COP by running it during the day. Depending on where you are of course, but in ChCh we probably only have a month of so of regular below-zero nights, so generally speaking the unit is hopefully not having to work in freezing conditions too often.

This is all un-quantified however!

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