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  1. #1
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    Geothermal Design



    Hey guys , so the plan is to build a new house . After plenty of research ive decided on radiant in floor for heating and to use geothermal as the heat source . I like the idea of building my own and have a prototype in the shed which is running pretty sweet at the moment. The under floor would have up to 5 zones as i would like to have different temps through the house and to compensate for heat that is gained in north facing living areas. (that zone shuts down) Now im thinking i could go a buffer tank or... i have just come across a vlt 6000 vsd that i could connect to my compressor and vary out put on demand required. This vsd has automatic energy optimization which i hope would help to increase efficencies and the soft starts may increase compressor durability and current draw.

    So just wondering if any one has thoughts on the best way to setup logic for controlling vsd for output of hotwater .
    Or if it is worth going down this road? , im pretty keen to get it into the system for the cool factor but thats just me , bit of a fridge geek.

    cheers Andy



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    Re: Geothermal Design

    One quick thought(so far)...we often design the pipework to take heat away from the over producing areas (solar gain) and move it to the other areas. Your over heated floor is a heat resource that can be used rather than shut off.

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    Re: Geothermal Design

    Yeah thats a good point mike.

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    Re: Geothermal Design

    Thinking over night ... as water supply temp nears set point slow down compressor (noticed with fixed speed prototype that approach temp increases near set point). Also in cooling mode reduce running speed so no short cycling , chilled water will go to a ducted ahu .

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    Re: Geothermal Design

    From all the other threads regarding VSD on standard compressors, I have come to believe that it is not a good idea (ask mad fridgie or Bigfreeze about it) and with a proper buffer tank (400-500L) a VSD is not necessary. I have one ASHP doing exactly what you are doing (see "my first self made EVAP) and with only a couple issues, which were control related, it is working splendidly.

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    Re: Geothermal Design

    Hi Andy,

    where about in NZ are you looking at building (important)

    My personal opinion is that the heat pump is the very last thing to consider in a hydronic heat pump system.

    May be you should a new thread, starting with a totally blank sheet, i am sure that the experts here could design the one of the best systems in the world. (lots opinion i would hope)

    cheers
    for PM

    Mad

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    Re: Geothermal Design

    Hello MF and all , we are in the Manawatu , not extreme by any means but can blow its a.. off when it needs to.
    House plans at this stage are for 240m2 , under slab insulation , edge insulation , aac wall construction , good quality window frames etc no holes in ceiling for lights .
    Was going geo for the fact it is something that i can diy , well be out in country as well so plenty of room to dig it up for horizontal ground loops, good soil conditions , wet clay , loam silt type .
    Ive had a thermometer in ground for 1 year at 1100mm , mid winter gets to 10c and is back up to 17c as we speak.

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    Re: Geothermal Design

    re3.jpg

    A pic of my prototype .

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    Re: Geothermal Design

    re4.jpgand another

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    Re: Geothermal Design

    Have you calculated your heat requirement maximum and average?
    I do not mean the standard sizing.
    How much energy do you need a day? Then how many run hours
    Do you have a log burner.
    What will be the SST of your geothermal heat pump.
    What is the average air temp over the heating season( you will be surprised), knowing this what will be you average SST with a air source heat pump.
    Are you looking at doing your DHW with this heat pump (I would)
    Also what are your 9or the wife) exceptions from this system. (clue they very slow in reacting to changes in temp)

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    Re: Geothermal Design

    How did you decide on your HX sizing?

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    Re: Geothermal Design

    They're great ground temps, you could get some serious efficiency from this system if you go about it the right way.
    First off you'd need the U-values you plan to obtain for the walls, roof, floor, windows etc. Then the min outside temp and the average outside temp.
    As MF said, the HP is the last thing to consider, the heat pump should match the house not the house match the heat pump. Get the basics right first then we can help you take it from there.
    Also, forget about zoning the house. The house will find its own level. Heat flows from warm to cold so unless you plan on sealing off each room, zoning makes no sense.

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    Re: Geothermal Design

    Ok great guys , thanks for those points . There is plenty to consider for sure , ok heat loss calcs done properly not just w/m2 . Will update when i have more info and it is progressing.

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    Re: Geothermal Design

    Average summer temperature is 21.8C (Night minimum temperature averages 9.4C below day maximum)

    Average winter temperature is 13.0C (Night minimum temperature averages 7.6C below day maximum)

    Palmerston North has an average 1,730 hours of sunshine per year (40% of possible hours)

    The climate is temperate

    Annual rainfall is 963mm

    Average 121 Wet days (>1mm) per annum

    Average 38 days per annum with ground frost (4 per year of -5C or lower)

    Annual average wind speed = 10.6kph (Windiest months are Nov-Jan, 12.5kph; and least windy Jun-Jul, 8.5kph




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    Re: Geothermal Design

    And coldest winter days?

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    Re: Geothermal Design

    Then it is a choice between air and liquid source, depending on budget, IMO. Still curious how you determined the HX size.

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    Re: Geothermal Design

    Hu AndyHX.
    I grew up in the Manawatu, remember the wind chill factor in the late winter/spring period, [ I remember it well ]
    You have and interesting project going on. With the building regs you will have double or triple glazed windows, and fully insulated structure.

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    Re: Geothermal Design

    Taking some assumptions.

    20C indoor temp
    Winter 180 days
    duty 2w/M2/C (C= indoor-outdoor)

    So base load.
    2*240*7= 3360 (24hours) (80.6Kwhr)
    Plus night load (difference between day temp and night temp)
    2*240 *7.6=3648 (12hours) (43.8kwhr)
    So your daily Base Load is 124Kwhr., lets say a standard design run time of 18hrs
    At this stage 6.9kw output
    But we do have 38 days of frost (-2C) (which really will only be night)
    Extra duty required 2*240*7=3360 (*12) (40.3kwhr)
    So leaving the run hours the same, basically nominal 10Kw output or the original selection would run 22.5Hrs.
    This presumes that the out put is constant (which we will go to later)
    the -5C periods I would ignore (as this likely to been overcome by the solar gain during the day "cold nights sunny days")
    Without doing a full dynamic design, any opinions on method so far (the rating is for a good home and would need to be confirmed for greater accuracy)

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    Re: Geothermal Design

    How can any assumptions be made yet, when we don't even know if he's building a passive house or a wendy house?

    10kw would be high for a house of 240sqm in those sort of ambients, unless the insulation is poor.

    If wind is the biggest factor in heatloss where you're building, then I would consider making the house airtight and using a HRV system.

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    Re: Geothermal Design

    This is NZ, double glazing is only recently been made standard, and we have massive windows. What is required is what is required to meet the losses.
    The sizing is irrelevant at this stage, but the method is and this then leads to what the SST and SCT temps are!
    based around the temps. The method determines whether air source or ground source.
    If you read fully. I gave 2 sizes 6.9 and 10,

    It is determining the method of sizing, choice of application and then equipment selection.

    The rest is just maths. (so just indicated a starting point)

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    Re: Geothermal Design

    Just to give you an idea how the NZ industry sizes heat pumps (christchurch)
    120w/m2 or 45w/m3
    ( Not my method)

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    Re: Geothermal Design

    Well then you need the U values of the windows, the walls, the floor and roof. When you have those you can size it accurately. Doesn't matter what country, thats your starting point. How can you decide what the losses are without the info?

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    Re: Geothermal Design

    We do not have the info, so I have made an assumption, which i also said we had to confirm. So well covered there. (if 1/2 or double does not matter it is what it is)
    So if we had the info we could size on the coldest day, decide your equipment on this coldest day. Is that the correct method. Or do you include diversity and or the annual running costs not just peak cost.
    The running cost must relate to SST and SCT, so we must know when load is required over time.
    Should he use ground source or air source, which will be more efficient, should he have variable refrigerant flow (inverter or digital)

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    Re: Geothermal Design

    His SCT will be totally dependant on the level of insulation he achieves. The better it is, the lower the temp he needs to produce.
    The method I would use would be calculate max heatloss and average winter heatloss. The HP should be able to handle the average winter day in about 8-10hrs run time per day. This leaves plenty of scope to cover losses in extreme weather but without being too undersized.
    If he insulates better and installs his ufh to the correct tolerences he should not need a flow temp of more than 32C in any conditions.
    I don't see the point in using an invertor in a house of this size. The scope of lowest power required and max power are too close to make a difference to the overall running cost and it would be easier to get the build wrong.
    Personally I'd wait for the insulation info before I'd spec anything. It makes such a huge difference it can't be ignored. Think it would also make the OP more aware of the importance of the total build as opposed to just the HP as NZ does seem to behind regarding this area. In the last five years heat pump sizes in Ireland have dropped by 30-40% due to changes in insulation alone

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    Re: Geothermal Design

    NZ house builds on average are some what lower in efficiency that say Europe. Basically money is spent on size and not always on quality. A mindset change is required.
    So your your ten hours running is this based upon, cycling over 24hours or thermal loading on set periods.
    If the second when would you choose to run it.
    If we presume again that the heating circuit and house insulation are the same for ground or air source.
    Ground source is great in the right application, but in some cases it is not the cheapest method of heating a house in the long term. But this statement has to backed up or evaluated. Hence we need a starting point.
    If SCT was the same for both sources, then it comes down to the SST.

  26. #26
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    Re: Geothermal Design

    Hey all,
    house construction will be r3.5 in walls, r3 in ceiling ,under floor r3.5.

    Hi Mike Holm , i use flatplateselect for hx sizing.

    I would base my SST at 0c , for a mid winter return water temp of 10c, 5k split and 5c approach, may be a little conservative. I will definitely get higher ewt at start of season and increased capacity.

    With correctly installed and designed under floor piping ( i would leave this to specialist installers ) i would base SCT at 40c.
    Last edited by AndyHX; 24-12-2011 at 07:13 AM.

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    Re: Geothermal Design

    What no windows.

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    Re: Geothermal Design

    Yeah will have some windows , r0.3 .

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    Re: Geothermal Design

    I'm still, unfortunately, using imperial R values for heat loss (eg: 5.5" of rock wool insulation is R-21) and Canada uses this RSI stuff that I can never get used to.

    Could you explain your insulation values to me please? I would like to get a handle on comparing our building codes with yours

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    Re: Geothermal Design

    Its based on cycling per 24hr period.
    Air source may well be better with the temps being quoted for this application.

    Are NZ R values the same a US R values?

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    Re: Geothermal Design

    for example a good triple glazed, double low E, argon (a bit above standard here) would have an R value of 4.5-5. U value is 1/r value. 100mm of urethane foam would be r-26 and is approximately our code requirement.

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    Re: Geothermal Design

    Zone 1 Zone 2 Zone 3
    Roof R-2.9 R-2.9 R-3.3
    Wall R-1.9 R-1.9 R-2.0
    Floor R-1.3 R-1.3 R-1.3
    Glazing (vertical) R-0.26 R-0.26 R-0.26
    Glazing (skylights) R-0.26 R-0.26 R-0.31

    these are the minimum standards in NZ for 3 different climate regions.
    copieed from wiki.

    Around most of the world, R-values are given in SI units, typically square-metre kelvins per watt or mK/W (or equivalently to mC/W). In the United States customary units, R-values are given in units of ftFh/Btu. It is particularly easy to confuse SI and US R-values, because R-values both in the US and elsewhere are often cited without their units, e.g. R-3.5. Usually, however, the correct units can be inferred from the context and from the magnitudes of the values. United States R-values are approximately six times SI R-values [2].

  33. #33
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    Re: Geothermal Design

    OK, using the 6X multiplier, our (Toronto, same latitude as northern California, verrrry different weather)
    would have the equiv code requirement for roof insulation of your 6-7, walls 3.5, floor is a new one for us as we almost always have a full basement and it is only common to put 1.5 or on under slabs of 2+, glazing must be double yours.

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    Re: Geothermal Design

    Merry xmas to all , NZ time any way!

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    Re: Geothermal Design

    White xmas in palmy?

  36. #36
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    Re: Geothermal Design

    It is here... Morning dudes, what under the tree?

  37. #37
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    Re: Geothermal Design

    A one week pass from dealing with heatpumps

  38. #38
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    Re: Geothermal Design

    I can't believe how many of us are on here on Xmas eve/day. Merry Xmas BF, have a pint on me, MF too

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    Re: Geothermal Design

    Hi all.
    a lot of interesting conversation on this post, Auckland had a blistering hot Christmas day.
    Hey, MF hope all is well at your place after all the quakes again the other day.
    magoo

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    Re: Geothermal Design

    Merry Christmas Mike, have a good one. Go easy on the mulled wine

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    Re: Geothermal Design

    Hi Magoo,

    House is OK, workshop is a bit of mess, "nothing changed, there then"

    Many spirits broken.

    thanks

    Mad

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    Re: Geothermal Design

    Hi MF.
    good to here you are all OK, what was it 4 shakes over 5.0 on the rechter scale, and the liquifaction would be soul destroying, I reacon the west has sunk half a meter by now. Emigrate north. But then again Auckland is made up of 30 + volcanic cones and blow vents, not a nice thought.

  43. #43
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    Re: Geothermal Design

    Hi everyone, the house design has come along quite a bit and we have floor plan sorted , i used this web site

    http://www.design-navigator.co.nz/

    to enter all construction details and it gave me a heat transfer of 383W/K. This does not include air infiltration and ventilation so with an HRV i expect up to 750W depending on air in / air out temps.
    So with a 20k inside to outside i have heat loss of 7660w + 750w = 8410w.

    Average summer temperature is 21.8C (Night minimum temperature averages 9.4C below day maximum)

    Average winter temperature is 13.0C (Night minimum temperature averages 7.6C below day maximum)

    Palmerston North has an average 1,730 hours of sunshine per year (40% of possible hours)

    The climate is temperate

    Annual rainfall is 963mm

    Average 121 Wet days (>1mm) per annum

    Average 38 days per annum with ground frost (4 per year of -5C or lower)

    Annual average wind speed = 10.6kph (Windiest months are Nov-Jan, 12.5kph; and least windy Jun-Jul, 8.5kph

    So it comes back to the question of source, geo or air?
    And what to base this on?
    thanks Andy




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    Re: Geothermal Design

    Howdy andy,
    Now it think it comes down to cost. If the budget can include ground loops, go for it. What I would rather see (just because of personal interest) is a ASHP with a solar hot water to bump up the COP when able. I love the idea of telling the utility to stick it up their a...... when the sun is shining.

    Oh BTW, look at the loop spacing fot the radiant. In an "normal" home here the typical installer wil have tubing at 300mm in a thick slab. I was really taken aback when BigFreeze and nd others would talk about 100mm but now I am a convert, well at least to 150mm anyway, sometimes closer. Check to see what the locals say about spacing.
    Last edited by MikeHolm; 14-05-2012 at 11:53 AM.

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    Re: Geothermal Design

    The answer is quite simple.
    Which system on average will have the highest suction pressure.
    150mm centers for me. and high water flow rates

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    Re: Geothermal Design

    On those temps you have to go air. They barely merit heating the house (I'm sure Mike would agree) .

    Get your ufh in at 100mm centers with loop lengths in the 80-90m range and 5K across your condensor and once your heat pump is set up well your COP should be off the chart.

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    Re: Geothermal Design

    Don't use HRV unless the house is air tight. Waste of money and a heat loss amplifier. Go Demand Control Ventilation instead

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    Re: Geothermal Design

    Geo source would still have a more stable temp , no need for defrost , no outdoor unit around the house. At start of heating season earth at 16c and end of winter 10c at 1m depth. With the demo geo i made i know that i can get really close approach temps , but with air i have not seen the same efficencies. so im still leaning to geo , and it will be somethig a bit different around these parts.

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    Re: Geothermal Design

    Big Freeze , how does demand control work , on internal humidity levels?

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    Re: Geothermal Design

    Hi Andy,
    I am installing one of my Boost units is Foxton in the next few days, do you want to catch up and look at your numbers
    cheers

    Mad

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