Topic: Underfloor heating

Underfloor heating 

I am interested in finding out the performance of examples of non-electric underfloor heating systems. We are drawing up plans just now and 'want to get it right'! But don't have much to go on. It seems hot water heat pumps might be the way but with amount of technologies and products appearing, it is hard to get unbiased advice. In Christchurch where we are, the air quality regs restrict us to a pellet burner (or diesel or gas). We want to build passively (timber frame with above code insulation) as possible and figure a hot water heat pump is the answer. Would be interested in hearing about systems with a 'track record'.

Re: Underfloor heating 

Underfllor heating is not new but there is a gentalman in Hasting installing solar underfloor heating. this is a good option and very affordable u can boost the heat during the colder two moths with gas or wood burner etc.

he installed a system into nine ecco units I have just built and has done the same for the levin city council new offices, Alternative heating is the company

Cheers
keith
harcourth holiday park

Re: Underfloor heating 

Hi Iam in Chch, I have used heat pumps for underfloor heating for at least 10 years. What to look for must in a HP, controlled refrigerant valve (TEV or electronic). Ozone freidly refigerant. Automatic defrost. Mainly someone who nows how to integrate heat pump technology and underfloor systems. (which is actually the biggest problem) Advice keep the underfloor system simple.

Re: Underfloor heating 

I can't work out how solar underfloor heating is supposed to work...........anyway we have just installed a hot water heat pump for underfloor heating and the results are outstanding, 200 square metres of house raised from 13 to 20 degrees in three days for around $12 - and something like a $60 a month cost for heating after this.
Underfloor heating with a heat pump is by far the most efficient way to heat a house at present, and as the last poster said...keep it simple.

Re: Underfloor heating 

Hi there,

We are building a house and it would be great to use underfloor heating with heat pump.
However it looks like to install gas is much cheaper. The gas installer think it would take approx 35years to get equal the gas and the heat pump. I am a little lost hear...
Jaykay can you tell the band and model of your heat pump and how much kW is the heat load??

Re: Underfloor heating 

Hi
As luck would have it I have just come out of a meeting with Snow Temp Heating Solutions in CHCH (Ray was the guys name). I suggest you give them a call to discuss your house and in slab water/heat pumps. I work for David Reid Homes and the clients wanted a good warm home without heat pumps blowing hot air everywhere and they don't want to use expensive electric in slab/under tile. I have talked to 10 different companies regarding these houses and these guys have given the best advice/solution so far. This is a good and efficient heating system that from what they say (and the blog below concurred) is very cost effective to run. My issue is that this company has not done many installs yet (they have 2 working in CHCH and 6 in construction), but the technology is tested up north and of course overseas.
An alternative for these same houses was in slab water pipes hooked up to solar panels and a diesel boiler (contact Alectra in CHCH and ask for Kaye Holt)
I hope this helps.
Ruth

Re: Underfloor heating 

These guys where at the Chch sustainble show at Rolleston and worth a look

http://www.climatezone.co.nz/contact.html

jeff@greentech

Re: Underfloor heating 

Here is an excerpt from a Waitakare City Council document:

"Theoretically, the ideal source of radiant heat would be the floor. Radiant floor heating based on warm water pipes set in a concrete floor slab runs on a low
temperatures of 40 - 50 degrees. It creates very comfortable warmth, especially round your feet, which need warmth most. However the response times are so long that underfloor heating is better for areas with a more consistently cold winter climate than Auckland has."

Does anyone know what they mean by the last bit about response times?

Re: Underfloor heating 

Response time is the difference when heat is applied to the water in pipes and when heat emits from floor. Pipe work installed close together in a thin concrete slab will have a faster reacting time then fitted in a thicker slab ( & pipes wide apart).

Solar heated underfloor works best with a slow reacting installation and a gas boiler system works better with a faster reacting system.

Jeff@greentech

Re: Underfloor heating 

Join the club as were are planning our house heating and another local (Oamaru) is doing the same.
Does anybody know of building details where insulation & heating pipes is laid above the slab and then a screed (50mm) is laid on top? The Europeans do it to speed up response times. Rib raft seemed a bit of overkill.

We came to the conclusion that the underfloor temp suits heat pumps and solar power was for the wrong time of year. As our night rate is 10c/kwh it could be used to heat the hot water as well. 300litres going from 15C to 65C = 50* 300 = 15kwh = $1.50. In theory a heat pump would be 40-50% of that on night rates & 70% in the day. Therefore we found solar too expensive when adding the interest cost + depreciation & the seasonal variation in efficiency. I think gas was around $2.80

The CCA put out a great book on a study of thermal mass Vs insulation Vs glass area. For the CHCH area the biggest influence was insulation so your insulation ideas are bang on. The further South you heas the less value thermal mass has as av. temp falls.

Re: Underfloor heating 

If you use a hot water heat pump for underfloor heating (by far the lowest running cost) use a thick slab. The response time is irrelevant. Basically the heat pump would be run for say ten or twelve hours during the day using the higher ambient temperatures and would therefore be more efficient. If you think about it, heating your house when it's cold is a bit stupid, don't let it get cold in the first place. Anyone who is mad enough to want use a fossil fuel for underfloor heating with a thin slab should have a rethink.

Re: Underfloor heating 

I Have had a heat pump water heater for a couple of years now it was a bit of a learning curve to set up at the time as nobody knew a thing about them. It's fantastic. Since then I've come across better ones made by Sanders Engineering Tauranga. I've not seen one in the flesh, nor have any connection, but they do seem to be the best idea yet. (I'd like them to make one with a wetback coil as well though).
Have a look.
Hey all you anonymous posters how about updating your profiles to have a real identity.

Re: Underfloor heating 

Forgotten my last login name, so I've started again.

The Sanders hot water heat pump is made in China and of limited use. The heat pump sits on top of the cylinder which sits inside the house, (noisy), and the output is very limited. The separate units that sit outside and can then heat the water in any size or type of cylinder already in a house are much more flexible. They also cost less than solar, are easier to install and save more energy.

We already have some hot water heat pumps installed with wetbacks as well, and I may be the only person with solar and a heat pump (but no wetback). The heat pump cost less than the solar and is far more reliable, (and probably saves more energy).

Re: Underfloor heating 

Underfloor heating via the thermal mass of the slab using unbed pipes is nonsense. The bottom half of the pipe is doing nothing but heating the ground. The thermal properties of the slab are such that this is pointless. Much better to use a ground source or aero thermal heat pump coupled with an above slab heating system that sits on insulation foil and then has a 20mm screed applied to the top. The temperature gain is very quick indeed.

Re: Underfloor heating 

If anyone was stupid enough not to put insulation under the slab and wanted a high energy bill then by all means use a thin top screed. This will work well if you use a fossil fuel as an energy source. With a thermal mass slab (thick), a heat pump can be used to heat the slab during the day when it is much more efficient and the energy released at night. The result? energy costs about 25% of other alternatives. Inslab heating isn't about quick response times, it's about efficient use of energy.

Re: Underfloor heating 

I agree with JK, insulation must be installed under the slab. But sadly today builders are still not doing this properly, a house just being build not far from me has slab hydronic heating but the insulation was only 25mm single layer of polystyrene around the edges. Seems hardly effective and not energy efficient as the signage outside the house would have us believe.

Re: Underfloor heating 

Are you saying there isn't any insulation under the slab? There must be. Heat travels through concrete 800mm in all directions, unless the slab is this thick it will be extremely wasteful. It would be interesting to know what the intended heat source is going to be. BRANZ recommend at least 75mm of expanded polystyrene under the slab, and 45mm wood round the edges.

Re: Underfloor heating 

The slab had 2400 x 1200 sheets of 25mm white polystyrene placed under around the perimeter of the concrete, not across the whole slab. So the ground in the centre is acting as a heat absorber which I guess would be fine if there was no water in the slab base course to conduct the heat away. This probably does work, but If it was my house I would have used 100mm across the whole slab and put 25mm polyisocyuranate R6 foam around the outside walls and foundations. I gues if your'e working to a budget its details like this that where corners are cut. Money saved in the short term is payed for many times over in the life of the house.
Crikey why are new houses being built with crappy insulation in the walls, minimal R3 in the roof and no double glazing. It doesnt make sense, if our lack luster govt was really serious about our countries long term energy efficiency then better insulation standards for new dwellings should be mandatory along with solar or heat pump assisted hot water cylinders.

Re: Underfloor heating 

YES well said. New Zealands building standards regarding insulation and heating options are shocking. A recent "Home Heating Options" information brochure produced by the government didn't even mention hydronic heating or underfloor systems. How bad is that!
New Zealand needs to get with the program when it comes to heating their homes and insulating them properly. It's funny cause people will spend $10000+ on multiple split-unit heat pumps to TRY and heat the whole house but they baulk at the same cost to put a zone control under-floor heating system in, weather it be fired heatpump or boiler driven !!!

Re: Underfloor heating 

I have a very basic question to ask you about underfloor heating. Whith water-filled pipes, how likely is it to require maintenance (cracked or burst pipes) and does this mean major excavations are likely? What is the track record on underfloor heating failures? What can be done to minimise this? Are their alternatives that are more robust?

Re: Underfloor heating 

In theory pipes in the floor come with a 50 year guarantee, but it will only be any use if someone is there to claim from! However as long as the correct pipe is used, and there are no joins in the slab - it is very unlikely anything will go wrong. A leak or two is in fact repairable by removing some concrete and fixing it. There are some horror stories from the UK (google) but it appears the wrong pipe was used - I've not heard of any inslab problems here in NZ.

Re: Underfloor heating 

I want to put 100mm of polystyrene across my slab before putting in the pipes.
Butting sheets of polystyrene together seems a little backward as they will never be perfectly touching and therefore make a thermal bridge.
Are there better solutions? i.e. 2 layers of 50mm sheets at right angles, or does someone make some sort of tongue-and-groove polysheet that can be joined together?

Re: Underfloor heating 

Use 4.8 meter sheets and glue the sheets together with polyurthene foam ( Gorilla or Hilti ), this foam has better insulation than the poly itself. If possible at the perimeter have the poly come up to meet the wall insulation., like they do in the steadfast system, this is vital so that the underfloor heat is force into the living space only. with out it ,go outside on a frosty morning and you will notice frost will not settled near the house. Foil will only work if you create an air gap.

-Thermal mass in the south
true the further south in winter you go the less efective, however in summer it gets quite hot and thermal mass is a blessing on those" its to hot to sleep nights". Nb- you can not have enough thermal mass, you can however not have enough insulation supporting it

- Underfloor Heating
Is not always ideal, carpet is an insulator, its slows down the heating and aids to the heat being lost to the perimeter. In summer, carpet stops the concrete floor from absorbing direct sunlight leading to a over heated room,. The slab is 100mm, therfore a slower response to heat and whats worse, a slower response to cool, that is , it manipulates your thermal mass, additional thermal mass without heating pipes in them is required so that it can do what is does so well, - self regulate the internal tempeture

Re: Underfloor heating 

Underfloor heating, which is the best system? There is not one.
As a troubleshooter on these systems, it has become obvious that designers are reseaching these systems, taking all the good points and coupling them together. They are not taking into account the negatives of each system. This is were the failures have occured.
Firstly you have look at your heat source. this determines what type of underfloor system and contol is required.
Most have designed the underfloor system then chosen the heat source.
Heat pumps (my fav.) need to supply warm water (for high efficiency) and high flow rates. Problem slow reaction time. "Slab control"
Boiler, high water temps, low flow. Problem over-shoot and piping layout critical,
Solar what a waist of time (for underfloor heating)
Insulation, very nice to worry about the joints, do not bother. Worry about the real losses not the walls or roofs "WINDOWS" reduce the area, tripple glaze or double glaze with curtains (ideally to the floor with enclosed pelmets), thermal break frames.

Re: Underfloor heating 

We are also looking at hot water UFH, best heat we ever had in our old house. Yes the reaction time is slow, but its designed to be. The 'problem' is more likely mis-selling by the agents I think. Underslab insulation and perimeter insulation are essential (person who asked about gaps - I think I answered you on the buildyourdream forum).

The system we used to have, utilised a high efficiency condensing gas boiler. It had high temp and low temp outlets and could modulate its output temperature depending on whether the DHW (80C) or the UHF manifold (45C) was demanding heat input.
Poster above - I'm not sure about your comment on Boiler.... You would not connect UFH directly to a boiler anyway, you need to circulate the floor circuit water and inject sufficient hot water to maintain the design floor temp. Type "underfloor heating manifold" into google for loads of info. I agree a HW heat pump would be a good option to supply steady heat over a long period. However using a woodburner with wet back gives you some "more or less instant" heat while the slab gets up to temp.

My intention is to use a thermal store, i.e. a large DHW cylinder with tappings for DHW and UFH. The heat inputs to this will be a wood burner wetback and solar (primarily for DHW rather than UFH). The control system will only allow UFH to demand heat if the thermal store is above a certain temp, so as not to reduce the hot water needed for showers etc. Solar would therfore give some advantage on sunny winter days.

I think I will need to have the thermal store designed, unless anyone can recommend a supplier. The control system combined with the solar controller will need to be fairly complex, but as I'm an electronic enginner I intend to design that myself.

Again, regardless heat source or ditribution technology, adding high R value insulation and plenty of thermal mass will produce a more confortable home than one withou these.