Browse Forums Heating, Cooling & Insulation 1 Dec 09, 2008 1:06 pm Hi,
Have read through numerous posts on the topic of hydronic heating but not come across any discussion of the relative merits of different options for the heat source to heat the water. We have pipes in slab and are building in an area in Tassie with no gas available. I was considering electric-boosted solar but was dissuaded by: - an evacuated tube solar supplier who thought Tassie lacks sufficient solar (ir?)radiation during winter to meet heating load; - the solar supplier's lack of experience with, and confidence in, electric (as opposed to gas) boosters; - the absoloute redundancy of the system during summer (unless we put in a mostly unwanted pool solely for the purpose of usefully dumping the excess heat); - price...thinking it might be better to invest the difference in additional solar panels, which provide flexible energy allocation (though will suffer during winter). In light of above, have decided to go with a heat pump hot water heater. Have read that their annual energy use is actually similar to electric-boosted solar. My questions for the forum are: What water storage capacity will I require? The house area is 241 m2. What is the role of an 'expansion/buffer tank' and is this needed if, say, I have 3*315 litre units? Do people have any experience with different heat-pump hot water brands for use in hydronic heating - performance, reliability, after-sales & warranty support? Less important questions are: Does it make sense to connect the heat pump/s to the offpeak tarrif (cheapest; limited periods) as opposed to HydroHeat tarrif (not quite as cheap but available 24hours/day)? Here is how I imagine it would work: heat up water during offpeak periods (ie overnight) - water circulates as slab/room temp drops (ie mainly overnight) - will water need to be reheated during the day? Not clear how this works. I've seen mention of using heat by-product from summer cooling as a boost for domestic hot water...are there standard set-ups to enable this heat transfer? Any advice much appreciated. Re: Hydronic heating - heat source 2Dec 09, 2008 5:13 pm Building in Tas relative merits of different options for the heat source to heat the water. building in an area in Tassie with no gas available. I was considering electric-boosted solar but was dissuaded by: - lacks sufficient solar (ir?)radiation - lack of experience with electric boosters; - redundancy of the system during summer - price. In light of above, have decided to go with a heat pump hot water heater. My questions for the forum are: What water storage capacity will I require? The house area is 241 m2. What is the role of an 'expansion/buffer tank' and is this needed if, say, I have 3*315 litre units? Do people have any experience with different heat-pump hot water brands for use in hydronic heating - performance, reliability, after-sales & warranty support? Less important questions are: Does it make sense to connect the heat pump/s to the offpeak tarrif (cheapest; limited periods) as opposed to HydroHeat tarrif (not quite as cheap but available 24hours/day)? Here is how I imagine it would work: heat up water during offpeak periods (ie overnight) - water circulates as slab/room temp drops (ie mainly overnight) - will water need to be reheated during the day? Not clear how this works. The first question is why have you chosen hydronic heating as your first option? Is it thermal comfort factor? A dislike of forced air systems? Quietness? Wishing to walk in bare feet? Personally if I had good solar access to the north face on the house, I would first ensure I had a passive solar design to heat the slab by direct sunlight. That is the cheapest option (thermal mass takes lots of energy to warm up) If you have neither ideal aspect or sunshine then hydronics may be an option. Solar hydronic systems are still evolving technology and quite expensive. I once read an article in the Alternative Technology Association's magazine about one. I have never come across a heat pump hydronic system. You will be probably attempting something ground-breaking. It may require some close discussion between the heat pump and hydronic techs about how to marry the systems together. I would be personally a little concerned about how many components are involved in the system. You may be a pioneer! You can get an idea of the performance of heat pumps by its REC number for your climate zone. If you go hydronic, it is a given that you insulate the house really well (including the slab edge to prevent heat leakage.). I would zone it so that you don't end up wastefully heating chunks of slab that won't be occupied for long periods of time. See discussion on: http://www.forums.envirotalk.com.au/ind ... topic=7704 Re: Hydronic heating - heat source 3Dec 09, 2008 6:08 pm Thanks dymonite69.
dymonite69 The first question is why have you chosen hydronic heating as your first option? Is it thermal comfort factor? A dislike of forced air systems? Quietness? Wishing to walk in bare feet? All the above! I want a solution that will provide a comfortable ambient temperature throughout the house, throughout the day and night, including during the worst weather conditions. We have already made the decision to use hydronic in-slab and are now seeking advice on the best heat source for the hot water. dymonite69 Personally if I had good solar access to the north face on the house, I would first ensure I had a passive solar design to heat the slab by direct sunlight. That is the cheapest option (thermal mass takes lots of energy to warm up) House is passive solar in that we have good orientation, appropriate eaves, floor to soak up sunlight, double glazing, good insulation etc. However there are still rooms on the south side of the house which will not get direct sun (due to block limitations & house layout preferences); and we are in a location which often has winter fog for much of the morning. dymonite69 I have never come across a heat pump hydronic system. You will be probably attempting something ground-breaking. I don't believe so; this type of system has been proposed to us by several hydronic installers. Of course, each installer has their own commercial arrangements which influence their recommendations on the type of heat pump; and there seems to be varying levels of expertise regarding approriate system sizing. Hence my query to this forum. dymonite69 If you go hydronic, it is a given that you insulate the house really well (including the slab edge to prevent heat leakage.). I would zone it so that you don't end up wastefully heating chunks of slab that won't be occupied for long periods of time. Agree. dymonite69 Thanks; reading of this discussion and others was part of my research in coming to the decision to opt for hydronic heating. However I haven't seen anything that specifically deals with the heat source for the hot water. Re: Hydronic heating - heat source 4Dec 09, 2008 10:39 pm There is a house in SA that uses solar EV tubes to heat water for in slab heating.
Can't remember the exact numbers - but I think it was 2000 litres of hot water in the system, and 3 times the normal # of SHWS EV Tubes. They then used a heat exchanger to ensure water quality in the tubes remained bug free - if you think about its and ideal breeding environment if not treated. So in essence the slab water was totally sealed and circulated through a coil that was inside the tanks. Here is a link to the house and they now have a DVD on it. House is owned by an eco architect. And that has what has been done with this house http://www.energyarchitecture.com.au/media/21-ada-st-documentary/ re the slab cooling down and warming up - you want it to stay at it's optimum - so do not plan on temperture ups and downs as this is not ideal - and as dynomite says - aim for solar gain on the slab. Options for other heat sources - wood fire that heats a boiler, or a heat pump as you say - but I'd prefer to see a well designed house that uses sun to warm the slab as much as possible. Steve Re: Hydronic heating - heat source 5Dec 10, 2008 9:13 am Yak_Chat Options for other heat sources - wood fire that heats a boiler, Yes I forgot about that one. If you have a good supply of renewable wood this would be a viable option. A wet back system could do both space heating and water heating. Later edit: The performance figures for heat pumps in water heating and hydronics in heating may give you a guide about what efficiency can be expected: http://www.sustainability.vic.gov.au/re ... system.pdf http://www.sustainability.vic.gov.au/re ... system.pdf http://www.sustainability.vic.gov.au/re ... eating.pdf I have always wondered if there are 'reverse-cycled' hydronic systems that do cooling as well. Re: Hydronic heating - heat source 6Dec 10, 2008 9:16 am Thanks Steve.
Yak_Chat There is a house in SA that uses solar EV tubes to heat water for in slab heating. ..Here is a link to the house and they now have a DVD on it. House is owned by an eco architect. Interesting that an eco architect did go for hydronic in-slab. Yak_Chat Can't remember the exact numbers - but I think it was 2000 litres of hot water in the system, and 3 times the normal # of SHWS EV Tubes. One thing I have been struggling with is that the sizing estimates that we've received are really inconsistent. Some talk about kW required; some talk about volumetric capacity, with storage capacity ranging from 315 litres + (unspecified) buffer tank up to 1500 litres. Argh! Yak_Chat They then used a heat exchanger to ensure water quality in the tubes remained bug free - if you think about its and ideal breeding environment if not treated. So in essence the slab water was totally sealed and circulated through a coil that was inside the tanks. Interesting point. Yak_Chat re the slab cooling down and warming up - you want it to stay at it's optimum - so do not plan on temperture ups and downs as this is not ideal - and as dynomite says - aim for solar gain on the slab. The plan is to set it at a suitable temperature (I guess maybe 19 degrees) during autumn and leave it on until late spring. I assume on solar gain days, the thermostat will register that the slab/room is already warm enough & hence not circulate the water; during this time the stored hot water will stay in the (insulated) tank and lose some marginal amount of heat, but not as much as when the water is circulating and transferring its heat into the slab; hence when solar gain is achieved energy will be conserved. So I don't really see passive solar gain as being mutually exclusive with active slab heating - unless someone can explain why? I have heard objections to slab heating along the lines that on warm days the house will overheat. However: a) I'm not really sure whether it works that way. ie if the slab is already (for argument's sake) 50 degrees C, and the sun delivers 15 degrees of heat, do they simply add together so that you end up with the slab being 65 degrees? Or is it more complicated than that? A question for a physicist I guess; and b) We plan to have air transfer vents that will allow air from warmer parts of the house to be transfered to colder parts of the house. Worst case scenario is that we switch off/down the zones that benefit from the solar gain IF the solar gain proves reliable enough over the winter period. Re: Hydronic heating - heat source 7Dec 10, 2008 9:23 am dymonite69 Yak_Chat Options for other heat sources - wood fire that heats a boiler, Yes I forgot about that one. If you have a good supply of renewable wood this would be a viable option. A wet back system could do both space heating and water heating. The thing with that is the emissions from burning the wood; also hassle of dealing with the wood, including petrol to collect it (we're on 1 acre and would have to source from elsewhere). So not a viable option for us. I would also think you'd end up with less stable heat & have that awful lag while waiting for the heater to get going (how long would the slab heat last after the fire goes out?) dymonite69 I have always wondered if there are 'reverse-cycled' hydronic systems that do cooling as well. That's what I'm looking at - I believe heat pump hot water systems are reverse cycle - same technology as heat pump air conditioners. Re: Hydronic heating - heat source 8Dec 10, 2008 9:53 am Building in Tas That's what I'm looking at - I believe heat pump hot water systems are reverse cycle - same technology as heat pump air conditioners. They are the same technology but I am not sure if you can reverse the heat exchanger of the water heater to make it cool the water as well. Re: Hydronic heating - heat source 9Dec 10, 2008 9:54 am dymonite69 They are the same technology but I am not sure if you can reverse the heat exchanger of the water heater to make it cool the water as well. Ah! Will look at that straight away as it was one of the reasons I was favouring the heat pump option. Re: Hydronic heating - heat source 10Dec 10, 2008 10:53 am Building in Tas One thing I have been struggling with is that the sizing estimates that we've received are really inconsistent. Some talk about kW required; some talk about volumetric capacity, with storage capacity ranging from 315 litres + (unspecified) buffer tank up to 1500 litres. Argh! a) I'm not really sure whether it works that way. ie if the slab is already (for argument's sake) 50 degrees C, and the sun delivers 15 degrees of heat, do they simply add together so that you end up with the slab being 65 degrees? Or is it more complicated than that? A question for a physicist I guess; and I am surprised that the hydronic guys can't do a proper heating load calculation. Having said that I heard that a lot of air-con dealerships can't do one either. The principle should be the same. 1) Determine the amount of energy in kWhr or MJ required to bring the slab to desired temperature and the rate at which you wish to reach this 2) Determine the amount of energy to maintain steady state (assuming constant heat losses through the building envelope e.g. walls, ceiling, slab, windows, door) 3) Estimate the losses due to inefficiencies from the system e.g. tank losses, water heater efficiency, pipe/duct losses They might also factor in additional supply of heat from solar radiation based on the orientation of the house and the windows that have solar access. The desired temperature of the slab will be based on your climate data e.g. daily mean temps and sunshine The thermal comfort and temperature calculations are quite complex and scientific. You just can't add them together like you have done. Essentially to get a slab hot enough to comfortably walk on with bare feet can result in a radiant temperatures that are too high for comfort. The sensation you feel with your feet (by heat conduction) is different from the heat radiating to the rest of your body and to the surrounding air. If you want some of the theory then check out my post on Thermal comfort on this forum. For more thermodynamic principles you will need to do some more investigating and find a source defining these terms: radiation, convection, conduction, thermal conductivity, emissivity, black body radiation, mean radiant temperature, black bulb temperature, dry bulb temperature, whole bulb temperature and operative or apparent temperature. The Bureau of Meteorology has some info on this. Re: Hydronic heating - heat source 11Dec 10, 2008 11:12 am Yak_Chat There is a house in SA that uses solar EV tubes to heat water for in slab heating. Can't remember the exact numbers - but I think it was 2000 litres of hot water in the system, and 3 times the normal # of SHWS EV Tubes. Later edit: Judging from the pics the front of house is facing east and the north side is abutting the neighbour's property i.e. poor solar access to north windows. Co-ordinates based on Google Earth are: 34°55'58.85"S 138°36'48.52"E I would expect this solar array to be about 90 tubes? Probably cost > $7500 for solar heater alone (not counting the hydronic system and other fittings). A good rule of thumb is that an ET system can heat about a third of its maximum water capacity to 60 degrees in the dead of winter. It probably would still need boosting despite its size to provide heating. A flat panel system can heat about one fifth of its capacity in winter. One of my references quotes a person from the radiant heat industry who warns don't buy a $10000 system that only provides $100 worth of heating! Good advice. Re: Hydronic heating - heat source 12Dec 10, 2008 6:39 pm Building in Tas Interesting that an eco architect did go for hydronic in-slab. An interesting article by the Oregon Department of Energy about the value of radiant floor heating in already energy-efficient houses. You may note that it on the US-Canadian border and ****** at higher latitude than Tasmania. Winters are probably colder there. http://www.oregon.gov/ENERGY/CONS/RES/tax/Radiant.shtml Re: Hydronic heating - heat source 13Dec 10, 2008 7:00 pm This from a person who has lived with hydronic heating (wall panels, not in-slab) most of her life in Europe: fabulous.
For the past year in Australia: disappointing. Do not have any figures to back this up, but houses here (even with all the 5 star requirements /what a load of bull/, double glazing, yes, big windows to the north, yes, big chunk of concrete facing north, it is still cold in the house. You can't compare European houses with Australian. Simple as that. So you don't get all the benefits of hydronic heating. Re: Hydronic heating - heat source 14Dec 10, 2008 7:37 pm mek with hydronic heating (wall panels, not in-slab) most of her life in Europe: fabulous. For the past year in Australia: disappointing. houses here (even with all the 5 star requirements /what a load of bull/, double glazing, yes, big windows to the north, yes, big chunk of concrete facing north, it is still cold in the house. You can't compare European houses with Australian. I think you you left out an important part of the equation. What was the heating source of the hydronic and how much energy was required to run it? I can make a cardboard box comfortable in winter by attaching a nuclear power plant to it. Re: Hydronic heating - heat source 15Dec 10, 2008 8:41 pm All the calculations for our house were done properly, I was led to believe.
What got me thinking about the whole thing was the fact in one of the windows threads where windowexpert confirmed my suspicions about double glazing and aluminium frames (I expressed my disappointment about draughts coming through our double glazed stackers). Now I don't understand a thing about U values (?) for windows and don't know if frame type is taken into account when hydronic heating calculations are done but obviously I have my doubts. From what I can recall, only type of glazing is considered. And this just got me thinking further... Sorry for hijaking this tread... Re: Hydronic heating - heat source 16Dec 10, 2008 8:51 pm mek All the calculations for our house were done properly, I was led to believe. if frame type is taken into account when hydronic heating calculations are done but obviously I have my doubts. Energy ratings and HVAC calculations always assume that the house is built 'properly' and the components aren't defective. Your leaky double glazed windows would have completely negated their effectiveness. Some say a leaky house is equivalent to a half metre square hole punched through the wall and letting the heat out. It would as useful as wearing a warm wooly parka with a big tear in the middle. Update 17Mar 11, 2009 3:33 pm Every time I read about hydronic floor heating in this forum it seems another keen starter has been diverted away from this option...
So anyway, an update: We have had the slab laid with the piping included. We went with a guy who quoted significantly less than others - something I am usually wary of but in this case was at the end of my tether trying to find someone with experience...and this guy provided a customer referee. Not much use as he turned out to be a hacker. Installed about half as much piping as is needed for our size - 450m of pipe for around 200m2 of floor space. I have since found out it is meant to be double that (every 200mm, not every 400mm on average). I'm not sure now whether this means we can still use it or not. I think I'll have to get an engineer to review for us. I've been told that it could cause issues with heat stress in the concrete slab due to uneven temperature distribution. But that it might be ok if we don't heat it too hot. Have also been told it's useless with solar (in Tassie) and we would have to have a heat pump. Not keen on that as they are a bit big, ugly & noisy for my liking. Also not really convinced about the 'Tassie is no good for solar' thing as we have the highest av insolation levels in the country I seem to recall...but then that might be summer-weighted. Anyway we are undecided & unimpressed, and are getting a wood heater, heat pump and provision for panel heaters. At least the pipes are there and if we can afford to install some means of heating the water for the hydronics at a later stage it might be an option. We have gone with solar hot water at least. Re: Update 18Mar 11, 2009 6:24 pm Building in Tas he turned out to be a hacker. Installed about half as much piping as is needed for our size I am sorry to hear about this. This is disappointing. How much did it cost you for the 1st fix? Perhaps you can get a genuine HVAC engineer to see how you overcome these limitations. Building in Tas Also not really convinced about the 'Tassie is no good for solar' thing as we have the highest av insolation levels in the country There are several sources for insolation including the Bureau of Meteorology http://www.bom.gov.au/jsp/ncc/cdio/cvg/ ... taticPage= http://www.gaisma.com/en/location/hobart.html http://www.apricus.com/html/insolation_levels_asiap.htm It is RECS Zone 4 which is the lowest one for Australia This is why the logic is flawed. If you are already struggling with sunlight, why pump the heat through a solar HWS transfer it to water and then circulate the heat into the slab. There would be less losses than just letting natural sunlight heat the slab directly via a large window. Building in Tas Every time I read about hydronic floor heating in this forum it seems another keen starter has been diverted away from this option... I strongly support energy-efficient design and technology but I can't see how it is a cost-effective solution. It may be a comfortable system but none of the objective data I have seen support the widely held belief that it is cheap to run. Re: Hydronic heating - heat source 19Mar 16, 2009 8:34 am Well, we have all the rest in place I think - good insulation, double glazing, northerly aspect, dark, textured tiles on the concrete floor to absorb heat from the sun...even thermalite in the interior paint (they make some pretty dramatic claims about energy savings/insulation factor...we'll see).
So the current plan is to just see how the house performs without any supplementary heating as we enter winter (should be finished by then I hope), then add whatever heating components we think we want/can afford based on the (dis)comfort levels we experience. I think that's the best we can do. Does anyone have a suggestion for a good hydronic in slab heating speacialist who may be able to help me with an existing system and wether or not it may need a seperator… 0 4881 Currently renovating, and our main lounge is 5m x 10m, with a cathedral roof peaking at 6.5m high. Currently have tiles on concrete slab. Room is very hard to heat. I am… 0 4812 |