Heat Pumps - post here.

offalygirl08 · 27-04-2012 4:19pm

hi, I am building a house and before I start work on the plans in detail I want to pick out a heating system for the house. May sound daft to some but its just to ensure I am not short on storage space from cylinders etc.
I was thinking about using Solar Tubes for the hot water, house will be based on a farm and hot water especially in summer months for showers will be needed.
I was also looking at the Air to Heat system. I was wondering if anyone is using this effectively and rough average of the bills. Bearing in mind that at the moment I am heating a 4 bed for 3K - 3.5K including ESB per annum.
My major concern would be also if anyone can suggest a supplier / fitter in Offaly or near by, I want a replicable one that has experience in putting them in properly and that if I will have some come back with.

steifanc · 28-04-2012 8:42am

mossy74 wrote: »

Hi All,
I have some questions some of you may have answers for.

I have a Ochsner heat pump for my geothermal heating system and on the information plate at the back of it, it says that it should use 3.6 KWh based on 20Amps at 230V with a power factor 0f 0.78. There is also another figure for the maximum current of 23 Amps.

My issue is that I have measured using a clamp meter a current of up to 28Amps (at 226V), I have also run some tests where I have switched off all circuit breakers in my house except for the ones used by the geothermal system. Taking account of shunt pump and controls the heatpump uses (measured over a few nights) approximately 4.8KWh. The supplier claims that this is due to a lot of heat loss in my house and that therefore the pump has to work harder. I think that this may be a fob off as the information plate clearly states that it should draw a max current of 23 Amps but to use 4.6KWh it must be drawing an average of over 26Amps. Has anyone else seen this? Is it normal? Will it affect the life of my heatpump etc. etc.

Just a quick note if it says 20 amps at 230 v it cant be 3.6 kw

Ohms law
Volts * amps = power

So
230*20 = 4600
Or 4.6 kw

Voltage is inversely proportional to current also so is your voltage goes down your. Current goes up
Where you gain with a heat pump is , its cost you 4.6kwh of electricity to get 13.5 kw of heat so that's nearly 3/1

I'm guessing your heat pump is around 13kw

johnfoyvision · 04-05-2012 8:21am

AckwelFoley wrote: »

There are 2 reasons why there are high esb costs on heatpumps.

1. The insulation of the house was not adequet or fitted poorly. (Its not a fob off) Its rather simple to proove. Get a Heat loss test done

2. The size of the pump is not adequet for the use. Each house needs to be calculated differently. As there are different specs for different house.

And more importantly.. having "good insulation" means NOTHING if its not fitted correctly If there are gaps in it you are as well have not fitted it at all as it causes a thermal draught

I am completely agree with your answer. I shall be thankful to all of you discussing heat pumps from which I get a lot of indormation. I am a student and I just studying about heat pumps and found this forum very useful that how we can implement the use of heat pumps by ourseld in real life.

sheff the ref · 08-08-2012 9:29pm

I used to work in Geothermal Heating back around 2005/2006 and am wondering if there have been many advances since then. I plan to build a 1800 square foot bungalow with a converted attic.

From my time in the business I know that ground source Geothermal heat pump with a properly sized, even slightly oversized horizontal ground source area will be very efficient. Excavation costs for the collector are expensive but the tidier alternative of a borehole collector will probably be more expensive though for a smaller house, the difference in cost may not be that huge. However it required top notch insulation and proper in-house heat management to make it run at its very very cheapest. At the time, underfloor heating was required to run it at the lowest costs. Has this changed. Are Rads still considerably more expensive to run using Geothermal??

At the time Air-To-Water was just coming in and was relatively unproven. Has it advanced much since then, and is it a viable alternative for a house of that size. How does it compare to Ground Source in terms of running costs?

In the two really hard winters of 2009 and 2010 which would have been the best option???

sinnerboy · 08-08-2012 9:55pm

sheff the ref wrote: »

In the two really hard winters of 2009 and 2010 which would have been the best option???

Honestly - a fossil fuel burning high powered boiler. Those winters were extreme and in my opinion only those with over sized plant stood any chance of keeping warm indoors without coats on.

Condenser · 08-08-2012 10:32pm

sinnerboy wrote: »

Honestly - a fossil fuel burning high powered boiler. Those winters were extreme and in my opinion only those with over sized plant stood any chance of keeping warm indoors without coats on.

Why do you say that? Plants that were performing well before those winters would have performed well through it.

To answer your question sheff, the technology has not really moved on but then again it doesn't really have to because the better performing installations are very cheap to run. Its generally the installation or application which lets systems down. So stay away from running rads of the units and stick with ufh. And a properly designed ufh at that. Not one designed towards an oil boiler installation.

Air to water will always be more expensive to run than ground source. Firstly there is the factor of having to run a fan motor to move air across the evaporator and also the factor that the energy source temp is variable. Colder outside temps mean all heat pumps have to work harder because of extra heatloss but air source have to work even harder again to overcome the fact that its extracting energy from colder air.

What has moved on is the insulation levels of homes. This in conjunction with air tightness means much smaller heat pumps can be used to heat comparable houses from 2005/2006.

sheff the ref · 08-08-2012 11:01pm

From my time in it, I would have to say that a properly installed and properly managed horizontal ground source system was the best allright.

The borehole would have been the tidiest to be honest. Hidden factors with horizontal collectors include the actual area that needs to be dug can be massive depending on the size of the house. Trees cannot be planted on that area either or it can never be concreted, meaning a massive area of grass to be cut.

sinnerboy · 08-08-2012 11:15pm

Condenser wrote: »

Why do you say that? Plants that were performing well before those winters would have performed well through it.

Because by definition plants that work well at external temperatures of -20 degrees are oversized for Ireland .

08-08-2012 11:32pm

How about these ?

http://dreamheatpumps.co.uk/12.5kw_heat_pump_HOME.html

3kw in 12.5 out, they say it's a direct replacement for an oil boiler. My oil boiler is about 6 years old.

50 degrees water temp is all I'd need at a maximum , cavities are pumped and 12 inches of insulation in the attic.

Seems like heat pumps are becoming more popular and starting to appear in clothes dryers and electric cars.

I worked it out that at 3 kw for 5 hours per day over 7 days for 6 months would work out at 403 euros per year of required heat. I would use the immersion as normal for the shower in summer. Oil costs around 440 for 500 litres and we get away with about 500 litres in a normal winter using it sparingly. We use the electric heater sometimes when we don't need to heat the whole house.

But if the heat pump was that good we could heat the house for longer with night saver and have a warm house for longer for less than oil ?

3 kw in 12.5 out ?

Condenser · 08-08-2012 11:42pm

sinnerboy wrote: »

Because by definition plants that work well at external temperatures of -20 degrees are oversized for Ireland .

Not true. A plant should be designed to cover the average winters day heatloss in an 8-12hr running period. That would leave an entire 12hr window to cover additional losses. You do not design plant to run 24hrs for your average winter temps. All plant should be designed with a degree of redundancy involved. Besides, that same plant will be then oversized for the remainder of the year but it doesn't effect efficiency or running cost. I'd don't see how you use your argument to support that an oil boiler would be more efficient.

Condenser · 08-08-2012 11:49pm

Deleted User wrote: »

How about these ?

http://dreamheatpumps.co.uk/12.5kw_heat_pump_HOME.html

3kw in 12.5 out, they say it's a direct replacement for an oil boiler. My oil boiler is about 6 years old.

50 degrees water temp is all I'd need at a maximum , cavities are pumped and 12 inches of insulation in the attic.

Seems like heat pumps are becoming more popular and starting to appear in clothes dryers and electric cars.

I worked it out that at 3 kw for 5 hours per day over 7 days for 6 months would work out at 403 euros per year of required heat. I would use the immersion as normal for the shower in summer. Oil costs around 440 for 500 litres and we get away with about 500 litres in a normal winter using it sparingly. We use the electric heater sometimes when we don't need to heat the whole house.

But if the heat pump was that good we could heat the house for longer with night saver and have a warm house for longer for less than oil ?

3 kw in 12.5 out ?

Chinese crap. Not even the top european air to water units have a COP of 4.6. And if you want to heat up to 50C the COP will drop by almost half. You wouldn't even buy the compressor and the fan motor for the price they're selling it for. You'd be as well off burning the money as you'd get more heat out of it and it'd cost you less.

Poor Uncle Tom · 09-08-2012 7:36am

Condenser wrote: »

Chinese crap. Not even the top european air to water units have a COP of 4.6. And if you want to heat up to 50C the COP will drop by almost half. You wouldn't even buy the compressor and the fan motor for the price they're selling it for. You'd be as well off burning the money as you'd get more heat out of it and it'd cost you less.

+1
One of the best responses I've ever read....

09-08-2012 9:07am

Condenser wrote: »

Chinese crap. Not even the top european air to water units have a COP of 4.6. And if you want to heat up to 50C the COP will drop by almost half. You wouldn't even buy the compressor and the fan motor for the price they're selling it for. You'd be as well off burning the money as you'd get more heat out of it and it'd cost you less.

Thanks for that, I guess it was too good to be true!

So are heat pumps for heating a waste of money and for now we should keep using oil and gas ?

It would have been good just replacing the oil boiler.

sinnerboy · 09-08-2012 10:24am

Condenser wrote: »

Not true. A plant should be designed to cover the average winters day heatloss in an 8-12hr running period. That would leave an entire 12hr window to cover additional losses. You do not design plant to run 24hrs for your average winter temps. All plant should be designed with a degree of redundancy involved. Besides, that same plant will be then oversized for the remainder of the year but it doesn't effect efficiency or running cost. I'd don't see how you use your argument to support that an oil boiler would be more efficient.

I never said an oil boiler is more efficient.

Otherwise we are on the same page. But the question asked was - what about the severe cold recent winters ? Whatever system you use it will either struggle to keep you warm and/r guzzle fuel to cope with those conditions.

I am saying that those with a gas or oil boiler during that period would not have seen the same spike in running costs compared to heat pump system.

A heat pump sized to average Irish winter temperatures , I believe , would struggle to perform and result in a big spike in ESB bills.

Now I am not arguing against heat pumps here . I fact I will say this - there is a flaw in the question - what about the extreme winters ? One should not design to that circumstance.

engineermike · 09-08-2012 12:15pm

Condenser wrote: »

Chinese crap. Not even the top european air to water units have a COP of 4.6. And if you want to heat up to 50C the COP will drop by almost half. You wouldn't even buy the compressor and the fan motor for the price they're selling it for. You'd be as well off burning the money as you'd get more heat out of it and it'd cost you less.

Fully in agreement with Condenser here - better to burn your money to stay warm than waste it on a cheap pump. You'll have a frozen ice box instead of a functioning compressor when harsh winters arrive again.
There are plenty of good air source pumps from reputable brands available on the market, the usual let down factors are poor installation of the pump, incorrectly matched for the property, poorly insulated property or in properly designed heat distribution system in the home. If all those boxes are ticked a heat pump will do as it says on the tin.
Also there are models with back up immersions in the pump to provide heat should there be a fault or abnormal external temp's - Ok your efficiency goes out the window at that point, however your house is warm & then you continue to make savings the rest of the year around.
Comparison graph of 2 models with COP at normal Irish mean temperatures & also COP at the 'harsh winter' temps experienced recently
( I'll PM the link to you, because there's manufactures detailed on the grpah, and i don't want to anoy the boards 'god's' )

mike f

09-08-2012 10:02pm

engineermike wrote: »

Fully in agreement with Condenser here - better to burn your money to stay warm than waste it on a cheap pump. You'll have a frozen ice box instead of a functioning compressor when harsh winters arrive again.
There are plenty of good air source pumps from reputable brands available on the market, the usual let down factors are poor installation of the pump, incorrectly matched for the property, poorly insulated property or in properly designed heat distribution system in the home. If all those boxes are ticked a heat pump will do as it says on the tin.
Also there are models with back up immersions in the pump to provide heat should there be a fault or abnormal external temp's - Ok your efficiency goes out the window at that point, however your house is warm & then you continue to make savings the rest of the year around.
Comparison graph of 2 models with COP at normal Irish mean temperatures & also COP at the 'harsh winter' temps experienced recently
( I'll PM the link to you, because there's manufactures detailed on the grpah, and i don't want to anoy the boards 'god's' )
mike f

Thanks I got the link, but I must admit I'm none the wiser.

I'm a bit clueless about heat pumps for instance what does cop mean ?

So if a heat pump used 3 kw and gives out 12 kw, I presume that's dependant on the outside temp and if it's -5 out would it be consuming more than 3kw ?

Bruthal · 09-08-2012 10:28pm

Deleted User wrote: »

Thanks I got the link, but I must admit I'm none the wiser.

I'm a bit clueless about heat pumps for instance what does cop mean ?

So if a heat pump used 3 kw and gives out 12 kw, I presume that's dependant on the outside temp and if it's -5 out would it be consuming more than 3kw ?

Its not so much that it gives out 12kw, but it transfers 12kw from one medium to another. The colder the outside temp, the higher the volume of the medium from which the heat is being extracted is required to pass over the evaporator.

A bath of room temp water has more heat in it than a red hot nail for example, even though the nail is at a far higher temp.

So 20,000 litres of air at 0 degrees C has more heat in it than 1000 litres of air at 20 degrees C (as a random plucked from the air example). So the lower the outside temp, compared to the inside one, the higher volume of air that would have to be passed over the heat pump evaporator outside, to maintain the same volume of air inside at the same temp.

The COP is the coefficient of performance, or the heat transferred compared to work input, or your 3kw v 12kw.

Condenser · 09-08-2012 10:29pm

Deleted User wrote: »

Thanks I got the link, but I must admit I'm none the wiser.

I'm a bit clueless about heat pumps for instance what does cop mean ?

So if a heat pump used 3 kw and gives out 12 kw, I presume that's dependant on the outside temp and if it's -5 out would it be consuming more than 3kw ?

Your COP is the coefficient of performance or how many kw heat energy you get out per kw electrical input. It can only be established at given criteria so for example the european standard for air to water is A2/W35 i.e an air temp of 2C and heated water outlet at 35C. If you decrease the first figure you will decrease the COP, if you increase the 2nd figure you will also decrease the COP. However the inverse is also correct, so your COP is not a set figure, its floating. A well designed system will aim to have the first figure as high as possible and the 2nd figure as low as possible to maximise COP. The problem with air to water is that the installer can really only control the water outlet (2nd) figure.

Consumption won't increase very much if the outside temp drops but energy output will as the energy is harder to collect when the air temp is low hence the reason that ground source units are a much better option, as both figures are in the hands of the installer.

09-08-2012 11:21pm

Thant's great info lads thanks.

Engineermike, in the link you sent me they quoted one of the units was able to heat water to 60 degrees with an air temp of -3 ? That seems incredible. Surely that could be a replacement for my oil boiler to heat the radiators ?

There are 2 units though which I don't understand, I get the heat pump one, but the other ? also they don't mention the electricity consumption.

I like the idea of using the pumps for cooling in summer, or when needed like now when it's warm and very humid.

engineermike · 10-08-2012 12:36pm

Deleted User wrote: »

Thant's great info lads thanks.

Engineermike, in the link you sent me they quoted one of the units was able to heat water to 60 degrees with an air temp of -3 ? That seems incredible. Surely that could be a replacement for my oil boiler to heat the radiators ?

There are 2 units though which I don't understand, I get the heat pump one, but the other ? also they don't mention the electricity consumption.

I like the idea of using the pumps for cooling in summer, or when needed like now when it's warm and very humid.

Hi,
You'd have to change the rads to forced air rads to have any real value from a pump that can cool during summer. Normal rads won't be effective and you find condensation being a problem on the traditional rads if you have a pump that heats / cools. - (during the cooling cycle).
The COP - basically means the work you will achieve i.e a cop of 3.5 means that for every 1 kw of electricity you pump uses - you will get 3.5 kw of heat & hot water into the property.

I'll send you a couple of other links that help explain it more clearly - the concept and useage figures for various pumps
mike f

Do-more · 10-08-2012 3:54pm

Deleted User wrote: »

one of the units was able to heat water to 60 degrees with an air temp of -3 ? That seems incredible. Surely that could be a replacement for my oil boiler to heat the radiators ?

There are some (mainly Japanese I think) manufacturers doing high temperature (HT) heat pumps which have two compressors working in series and can output water temperatures up to 70C. I've seen them mentioned on some UK forums where they seem to be a popular retrofit for oil and gas boilers but haven't noticed them mentioned on here. It might be worth your while searching for feedback on them.

10-08-2012 9:19pm

Thanks for the replies lads, I'm sure this technology will only improve in the future.

Direct boiler replacements would be what I'd be looking for. I live in a mid terrace house so I wonder how loud they would be ? Luckily enough it's not hard to heat and the cavity insulation and attic insulation has made a noticeable difference, however my windows are old and pretty rubbish and are in bad need of replacement, so I think I'd be far better off for now upgrading them to modern windows. However if a heat pump could heat the house as cheap or cheaper than oil I would be very happy. Our oil consumption is around 500-700 litres a year, with the heat being on 4-5 hours per day. Id does warm up quick enough as it's small enough 3 bed terrace house and being a mid terrace I only have 2 external walls.

The rear of the house is south facing and even in the coldest of winters if the sun shins in the back of the house it's very warm.

I think I got a C for my energy rating, the windows knocked it down a few points but I could possibly get a high C or possibly B with decent windows.

The plan down the road is to build or renovate to fully passive standards with heat pump and solar P.V and wind turbine.

sheff the ref · 11-08-2012 10:39pm

Condenser wrote: »

Your COP is the coefficient of performance or how many kw heat energy you get out per kw electrical input. It can only be established at given criteria so for example the european standard for air to water is A2/W35 i.e an air temp of 2C and heated water outlet at 35C. If you decrease the first figure you will decrease the COP, if you increase the 2nd figure you will also decrease the COP. However the inverse is also correct, so your COP is not a set figure, its floating. A well designed system will aim to have the first figure as high as possible and the 2nd figure as low as possible to maximise COP. The problem with air to water is that the installer can really only control the water outlet (2nd) figure.

Consumption won't increase very much if the outside temp drops but energy output will as the energy is harder to collect when the air temp is low hence the reason that ground source units are a much better option, as both figures are in the hands of the installer.

Therefore even in extreme conditions, the temperature of the ground is pretty much constant in winter time when the horizontal pipes are laid roughly 1metre under the ground or down a borehole. The chilled liquid is sent out into the ground and the ambient temperature takes the cold sting out of it, and raises the temperature by a couple of degrees in the collector.

Air Temperature went as low as -10 and possibly lower in the winter of 2010. How much more expensive would the Air to Water system be to run during such a cold spell per hour of heat produced. Would there be much of an ESB cost difference from say +2 degrees, to 0 degrees, to -2 degrees, to -4 degrees to -6 degrees to -8 degrees to -10 degrees.

For initial investment purposes the decision to be made is, to evaluate if the occasional cold snap is worth taking a hit on with an Air to Water system, when compared to the excavation/well drilling costs for a Ground Source system.

Condenser · 13-08-2012 12:21am

sheff the ref wrote: »

Therefore even in extreme conditions, the temperature of the ground is pretty much constant in winter time when the horizontal pipes are laid roughly 1metre under the ground or down a borehole. The chilled liquid is sent out into the ground and the ambient temperature takes the cold sting out of it, and raises the temperature by a couple of degrees in the collector.

Air Temperature went as low as -10 and possibly lower in the winter of 2010. How much more expensive would the Air to Water system be to run during such a cold spell per hour of heat produced. Would there be much of an ESB cost difference from say +2 degrees, to 0 degrees, to -2 degrees, to -4 degrees to -6 degrees to -8 degrees to -10 degrees.

For initial investment purposes the decision to be made is, to evaluate if the occasional cold snap is worth taking a hit on with an Air to Water system, when compared to the excavation/well drilling costs for a Ground Source system.

Plus you have to factor in the fact you have more moving parts (fan motors, 4 way valve etc) that can go wrong. And also that the outdoor unit will be exposed to the elements year round and so is unlikely to have a lifespan of more than 10yrs. The cheaper units will look very rough even before then.

sheff the ref · 13-08-2012 12:29pm

Ya. That is the issue allright and a very valid point. A ground source heat pump can be indoors either in an internal Boiler House well free from all elements or in the Garage.

An external Oil Boiler is well protected and sealed from the elements in fairness but an Air to Water Heatpump cannot be protected, because it needs to be exposed to operate. Anything exposed to the weather in Ireland is subject to all forms of long term maintenance issues, like you said there are hidden costs such as replacing wear and tear parts. The likelihood is that in say 10 years time time a new heatpump may well be a cheaper option than replacing parts, because like a washing machine, once one goes, they all go.

I think ground source may well be the best option.

Bruthal · 13-08-2012 7:39pm

Condenser wrote: »

Plus you have to factor in the fact you have more moving parts (fan motors, 4 way valve etc) that can go wrong. And also that the outdoor unit will be exposed to the elements year round and so is unlikely to have a lifespan of more than 10yrs. The cheaper units will look very rough even before then.

The specific heat capacity of air is 4 times less than water per gram as well, and a gram of air is a lot higher volume than water, so a condensor collecting heat from ground water will likely be more efficient than an air source one, besides the more stable ground temperature as well.

13-08-2012 8:48pm

robbie7730 wrote: »

The specific heat capacity of air is 4 times less than water per gram as well, and a gram of air is a lot higher volume than water, so a condensor collecting heat from ground water will likely be more efficient than an air source one, besides the more stable ground temperature as well.

Would it be possible to integrate the heat pump into a normal well ?

Drilling a well specifically for the heat pump would be really expensive but would probably be better than laying pipes over a large area of the garden ?

Condenser · 13-08-2012 9:26pm

Deleted User wrote: »

Would it be possible to integrate the heat pump into a normal well ?

Drilling a well specifically for the heat pump would be really expensive but would probably be better than laying pipes over a large area of the garden ?

Amost neglibibly more efficient once the ground conditions are right.

You could use a water to water system with a standard well but you'd have to drill a dump well and have high quantities of mineral free water such as lime, iron etc

13-08-2012 9:33pm

Condenser wrote: »

Amost neglibibly more efficient once the ground conditions are right.

You could use a water to water system with a standard well but you'd have to drill a dump well and have high quantities of mineral free water such as lime, iron etc

Thanks for the answer.

So am I guessing that the most efficient way to use heat pumps is ground pipes and underfloor heating ?

Condenser · 13-08-2012 9:59pm

Deleted User wrote: »

Thanks for the answer.

So am I guessing that the most efficient way to use heat pumps is ground pipes and underfloor heating ?

Yes, as horizontal systems are cheaper and ufh can be run at very low temps if designed correctly.Poor installers can mess up other areas of the system but once these fundamentals are right, fixing any problems caused by an incorrect install is possible and relatively cheap.
But put time into choosing your installer and get it right first time.

sheff the ref · 14-08-2012 12:53am

Deleted User wrote: »

Would it be possible to integrate the heat pump into a normal well ?

Drilling a well specifically for the heat pump would be really expensive but would probably be better than laying pipes over a large area of the garden ?

You need a very deep borehole to provide the same collector area as a horizontal ground collector with sealed circulation pipework. A normal well would not have that depth.

However I believe you can use an open pipe system but that could cause its own problems. Dirty Water. Preventing Freezing etc.

fairwind · 21-09-2012 4:13pm

Hi
Looking at possible borehole collector geothermal
Any ideas on costing and running .
We're close to sea in west cork
Might this help us in perhaps shallower hole required if we hit close to seawater?
Also we plan on ufh in 290 Sqm house well insulated.
Don't want oil so it's this air water or possibly Lvp solar.
We would hope to future proof by eventually running pump from photovoltaic.
F

sheff the ref · 22-09-2012 9:36pm

For the liquid leaving the heatpump, you need X amount of surface area of closed loop pipe for the liquid to circulate sufficiently. That applies regardless of the ground conditions so you cannot take short cuts on the length of pipe needed for the collector.

The exception is if you are actually pumping through an open loop e.g sucking into the heatpump from one side and blowing out the other. Wouldnt fancy doing that with salt water.

fairwind · 22-09-2012 10:00pm

Thanks for the info, I was wondering would the proximity of the sea improve COP. I understand that an open loop is not a good idea with salt water.
Have you heard anything re the heliotherm system? Thanks
F

sheff the ref · 23-09-2012 8:59pm

Havent met anyone with a working Heliotherm system and if I was to invest in any system I would need to talk to a few people who had them working through the cold winter.

badgerhowlin · 24-09-2012 7:30am

fairwind wrote: »

Hi
Looking at possible borehole collector geothermal
Any ideas on costing and running .
We're close to sea in west cork
Might this help us in perhaps shallower hole required if we hit close to seawater?
Also we plan on ufh in 290 Sqm house well insulated.
Don't want oil so it's this air water or possibly Lvp solar.
We would hope to future proof by eventually running pump from photovoltaic.
F

PM sent

cwboy · 08-10-2012 6:45pm

Hi. I am principal of a school who have been offered grant aid to install renewable energy. One of the options proposed was four air to water heat pumps to replace our oil boiler. A Borehole was mentioned but was almost ruled out on time and cost constraints. The school was insulated with fiberglass in flat ceilings and walls pumped three years ago.

We also plan on installing pv panels to take some of the burden on electricity.

What are peoples opinions on this option? The school has twelve classrooms and a multi purpose hall along with other space. The level of grant aid would not cover the works and the school would have to cover 20% of the cost.

Thanks

al2009 · 08-10-2012 7:08pm

Depending on oil usage then yes, fairly straight forward retro fit, it may be possible to retain existing rads. What part of this green and pleasant land are you in?

Condenser · 08-10-2012 11:12pm

If you are running existing rads I would advise against it. The temp required would be too high in order to get a good return. Your COP would be very low especially on A2W. Its likely that a school would have poor insulation values also which would further reduce the chances of running at a decently low temp. In times such as these its hard enough for schools to have money for the important things. You're money would be best spent elsewhere in this case imo.

Alot of HP suppliers are trying to market heat pumps as straight swap solutions for oil boilers. They are the furthest thing from and need to be installed in the right manner in the right application. I met with two potential customers with similar proposals in domestic situations just today and advised both of them not to bother with a HP as the application did not suit.

cwboy · 09-10-2012 1:52pm

Thanks for the replies.

I am based in Carlow. The school is reasonably well insulated but doors would be open at breaktime leading to heat losses. With grant aided funding, would we be foolish to ignore a way to rid ourselves of oil? The oil bill is around seven thousand a year. The installer reckons we can elimate 80% of this with the heat pumps.

Are the photo voltaic panels good enough yet to really help with the electricity burden?

Condenser · 09-10-2012 7:49pm

cwboy wrote: »

Thanks for the replies.

I am based in Carlow. The school is reasonably well insulated but doors would be open at breaktime leading to heat losses. With grant aided funding, would we be foolish to ignore a way to rid ourselves of oil? The oil bill is around seven thousand a year. The installer reckons we can elimate 80% of this with the heat pumps.

Are the photo voltaic panels good enough yet to really help with the electricity burden?

Your installer is talking through his proverbial in that case. You won't reduce you bill by 80% with an A2W heatpump in even the most perfect of circumstances and certainly not in the application you have explained. I'd be surprised if you ever broke a COP of 3.5 on that system. You need a COP of 2.2 just to be the equivalent of oil.

PV doesn't stack up for a residential set up at the moment because there is no decent feed in tarriff available and therefore the payback just isn,t there. You'd just be paying for your next 15yrs electricity up front. However in your case if you're getting grant aided it is certainly an option worth exploring. It all depends on how much panel you will get for the grant provided as a deciding factor in whether you choose pv or not.

al2009 · 09-10-2012 8:24pm

cwboy

It would be a good move, 80% might be optimistic. I can pm the number of a company that have carried out comparisons on oil vs hp for nursing homes and similar buildings.

alec

Condenser · 09-10-2012 10:00pm

al2009 wrote: »

cwboy

It would be a good move, 80% might be optimistic. I can pm the number of a company that have carried out comparisons on oil vs hp for nursing homes and similar buildings.

alec

Al i'm surprised that a man with your background would be endorsing installing a HP on a system where the condensing temp would be so high constantly and on a building especially an A2W systems with the potential for deep evaporating temps and a propensity for icing of the condensers, especially in our humid/moist conditions . Would these heat pumps be ran in series and if so what would the defrost strategy be as you could not have one defrosting while the others are heating.
What would you consider would be the lifetime of the compressor of a unit condensing at 50C for such extended periods of time?

cwboy · 09-10-2012 10:01pm

al2009 wrote: »

cwboy

It would be a good move, 80% might be optimistic. I can pm the number of a company that have carried out comparisons on oil vs hp for nursing homes and similar buildings.

alec

Thanks for the reply. Would love the number if you could pm it. Having spoken to one of the installers today he said the rads would be between 20 and 45 degrees depending on the outside temp and could be boosted by oil if needed. The rads would be on all day to maintain a constant temp.

Outkast_IRE · 09-10-2012 10:12pm

cwboy wrote: »

Thanks for the reply. Would love the number if you could pm it. Having spoken to one of the installers today he said the rads would be between 20 and 45 degrees depending on the outside temp and could be boosted by oil if needed. The rads would be on all day to maintain a constant temp.

Honestly the only way you could prove this system would work is to forget about installers advice etc, salesmens advice, and hire in a comapny to do a full energy audit, you would advise them that your looking to reduce heating costs of the building etc.

And let them do their audit and they should be able to tell you straight up what your alternatives are, no BS , no salesmen/installer advice.

Personally i am having a hard time seeing how you would save money with the air to water running 24/7 , especially with kids in the buildings where they will be constantly in and out of classrooms etc.

All your rads were sized day one to run at a certain temperature, if you drop this temperature there is a sizeable chance rooms will be cold , especially coridoors and larger areas such as halls etc.

Also the installer telling you 20 to 45 degrees , sure a 20 degree rad wouldnt heat a room very well at all !! and lets assume the oil boosts it then your back to square one using oil to supplement a brand new system, not to mention you will have the maintaince of both oil and air to water now!!

As i said, proper energy audit is the only way to go with the audit focused towards choosing possible new systems.

Condenser · 09-10-2012 10:30pm

cwboy wrote: »

Thanks for the reply. Would love the number if you could pm it. Having spoken to one of the installers today he said the rads would be between 20 and 45 degrees depending on the outside temp and could be boosted by oil if needed. The rads would be on all day to maintain a constant temp.

You wouldn't even get heat off ufh at 20C. If you put your hand in 20 degree water it would feel cold and it is. Body temp is 37 degrees so as a consequence if you stood in a room naked you would be giving off more heat than a rad of similar surface area at 20C.

Outkast_IRE · 09-10-2012 10:38pm

Condenser wrote: »

You wouldn't even get heat off ufh at 20C. If you put your hand in 20 degree water it would feel cold and it is. Body temp is 37 degrees so as a consequence if you stood in a room naked you would be giving off more heat than a rad of similar surface area at 20C.

Exactly what i was pointing to..........

The rads are sized to work at a set temp, at this set temp they will heat the building.

These installers now say , it will work 20 - 45 degrees and then you can boost with the oil !!!!!!!!!!
Honestly its along time since i heard such ****e.

This building would end up using a hell of a lot of oil , and would need the additonal expense of a buffer tank probably so two different heat sources can contribute to the same building.

hugo29 · 20-11-2012 4:26pm

is there any way to determine what depth boreholes are. we have geothermal system but we dont seem to be getting a decent temp in from them

sheff the ref · 20-11-2012 5:18pm

Basically a borehole has to compensate for the surface area that would be achieved by a horizontal collector to meet the requirements of a heatpump of a given size. I was involved with a job where there were 4 if not 5 boreholes and from memory I think they were 200m deep each.

I have specs somewhere for borehole depths needed for heatpumps with different KW. I do know at the time that collectors were being undersized in a bit way by different companies, and perhaps that has happened with boreholes.

The temperature from the heatpump should be relatively constant regardless of whether the collector was undersized or not. Basically the difference an undersized heatpump would make is that the pump keeps circulating the waterantifreeze working harder to get the temperature gain, hence drawing electricity and doesnt get much of a chance to cut out. That wouldnt really affect the temperature heading to the internal heating though I would have thought which should be roughly 40 degrees

hugo29 wrote: »

is there any way to determine what depth boreholes are. we have geothermal system but we dont seem to be getting a decent temp in from them

engineermike · 20-11-2012 7:42pm

sheff the ref wrote: »

Basically a borehole has to compensate for the surface area that would be achieved by a horizontal collector to meet the requirements of a heatpump of a given size. I was involved with a job where there were 4 if not 5 boreholes and from memory I think they were 200m deep each.

I have specs somewhere for borehole depths needed for heatpumps with different KW. I do know at the time that collectors were being undersized in a bit way by different companies, and perhaps that has happened with boreholes.

The temperature from the heatpump should be relatively constant regardless of whether the collector was undersized or not. Basically the difference an undersized heatpump would make is that the pump keeps circulating the waterantifreeze working harder to get the temperature gain, hence drawing electricity and doesnt get much of a chance to cut out. That wouldnt really affect the temperature heading to the internal heating though I would have thought which should be roughly 40 degrees

As sheff has proposed this information is accurate - however if your not reading optimum temp differential at the pump computer (flow and return at the energy / loop - ground loop), there may be an issue with undersizing.
The manufacture of the pump & the KW of the unit (model no. also).
Distance from bore hole to inspection chamber and return to the pump.
Last time you had the unit serviced ?
These details would be helpful to provide an accurate answer of your probable issue.
Rgds,
Mike F

Heat Pumps - post here.

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