geothermal, underground collectors or air to water

weston1

hi,

looking at getting a geothermal system for new build. does anyone know how good the air to water systems are, especially in temps below zero. i get mixed answers some say good others not very effective at low temps. would like to hear from people who have the system in or have done a lot of research into it. i have talked to people with the ground collectors and it seems a good system, the installation of the air system cheaper but is it worth it. thank you

heinbloed

ALL heating systems should be seen as a whole.
So the energy demand is your first point to figure out, a HP installer/seller in Ireland is hardly able to do that and you can be sure to get an underperforming heating system. Either the HP is choosen to big and to expensive or it is simply not delivering enough thermal energy to cover the demand without back-up.

To make sure that you don't deal with cowboys ask them for a written and signed guarantee on the electricity consumption (in kWh per year) of YOUR heating system in YOUR house. Hear-say about references won't do. Exact numbers. In writing.
And you see them bucking out.....

Plombier

With ground source if the collector is sized correctly it wont notably decrease the temperature of the ground around it in a heating season, so the performance of the heatpump remains the same throughout the year COP 4.5 , with an air source heatpump at 15 degrees producing 45 degrees might have a COP and if it has an output of say 16 KW, but if its -10 degrees out and the airsource is producing 45 degrees water its output will drop to about 8 KW and a COP of about 1.75, if you take 5 degrees as an average winter temperature the airsource will give 12 KW and a COP of 3, so its all about the COP, if your building needs 20000 KW for a heating season then the ground source will need 4400 KW of electricity whereas the airsource will need maybe 7000 KW of electricity,
if your building needs 5000 KW for a heating season then the ground source will need 1100 KW of electricity whereas the airsource will need maybe 1750 KW of electricity, you will need to know the heating season load for the building before you can make your decision.

heinbloed

Here a typical method how to screw up an energy demand/ heating system performance calculation :

..... and a COP of 3, so its all about the COP, if your building needs 20000 KW for a heating season then the ground source will need 4400 KW of electricity whereas the airsource will need maybe 7000 KW of electricity,
if your building needs 5000 KW for a heating season then the ground source will need 1100 KW of electricity whereas the airsource will need maybe 1750 KW of electricity, you will need to know the heating season load for the building before you can make your decision.


Forget the COP.
We are looking for the heating system's performance.
Such a "calculation" as above is not worth the paper.
Contact a heating engineer. There are EN standards for this issue, demand them to be the base of the calculation.
The borehole/ surface will of course cool down over the years, this factor is not included in the EN standards.

Again: demand a written and signed guarantee on the electricity consumption of the entire heating system. And if you're lucky to find a seller/installer willing to sign ask on what base his calculations were done, let us know.

weston1

tk u. that does make it look like the air source is more expensive, and as we have no control on future weather we cannot predict bills as accurately with the air source. the cop of the air source is then very dependent on temp and it can affect it greatly if cop could drop as low as 1.75. the house is 380sqm, 4inch wall cavity which i will get pumped and i will put up the cosyboard on the inside of external walls. will also be getting as good a window as i can. i'm only at first story block level as of yet but insulation will be priority

weston1

hi heinbloed,

is it possible to get an engineer to give those written guarantees or effectively be that accurate at working it out. i assume it would be done when your house is finished, but the system would be in and paid for by then

heinbloed

Weston1 asks:

is it possible to get an engineer to give those written guarantees or effectively be that accurate at working it out. i assume it would be done when your house is finished, but the system would be in and paid for by then

Yes, but he/she will only guarantee that his calculation is correct. He/she will not guarantee that your heating system is working according to his calculation. Unless he/she is also the installer.
You have to get this guarantee from the installer. Who in turn might have to consult an engineer.

The one who get's the money for a functioning heating system is the one who has to guarantee it's performance.

Plombier

Yes what heinbloed was saying is what I was trying to point out, and yes you can make the calculations before the system is specified or installed, your architect should have the U values etc. for your installer to correctly size the system and calculate running costs.

weston1

taking that on board is it possible then to work it out accurately for the air to water as temp is outside their control. does the temp have a big effect on those systems, some say no (the sellers) some say yes(again sellers). a cop down to 1.75 is quite low. they talk about cheap night rate electricity but with the very sub zero the last no. of nights this air to water may not be a good system. i just wonder what the efficieny of those systems are in differing temps

heinbloed

Plombier wrote:

...for your installer to correctly size the system and calculate running costs.

No one can calculate the running cost, plombier. Only the electric energy demand can be calculated. This unit is called Kwh , not "KW" or Euros or hand shakes or whatever....

But ask for the price of a full 10 years 100% service contract incl. spare parts and VAT from the reputeable HP manufacture, including the ENTIRE heating system, they offer this.
(Propably on eye-opener....)

Not from the installer, they come and go.

Plombier

Yes it

Propably

is a Kwh not a KW

heinbloed

Weston1 asks:

taking that on board is it possible then to work it out accurately for the air to water as temp is outside their control. does the temp have a big effect on those systems, some say no (the sellers) some say yes(again sellers). a cop down to 1.75 is quite low. they talk about cheap night rate electricity but with the very sub zero the last no. of nights this air to water may not be a good system. i just wonder what the efficieny of those systems are in differing temps

Again: get everything they claim in writing. If they claim for example a future electricity price then get this in writing. You will see them walk out. Similar as if asking for a guaranteed heating system's performance ...

These people make a living by selling, be aware of this.

Plombier

Again it comes down to how much energy it is going to take to heat your house, if your energy demand is small the the difference will not be great but if you have a very high demand its more crucial.

weston1

but i suppose again if my house is insulated well and do my best to keep it very efficient, the air to water system is it efficient enough with those low temps. i suppose that is my main query the effectiveness and efficiency of air to water. i know its hard to answer completely without all the i's dotted, but air to water systems as compared to underground collectors

heinbloed

but i suppose again if my house is insulated well and do my best to keep it very efficient,

Well, you might still have not understood the issue: the insulation is non-relevant when it comes to the thermal energy usage.
The thermal energy usage depends on the demand. And supply.

Get a heating engineer in. Or a civil engineer, an energy advisor ect..

They will give you the min. and max. demand (in kW) and the anual demand (in kWh) which your heating system has to cover.

Without these numbers you can't make a decision based on logic.

Plombier

Yes the ground loop is more efficient, if your house needs 40000Kwh per year for heating if the average COP for ground loop is 4 then it will take 10000 units of electricity most at night rate and some day rate average price €0.10 per KWH costing €1000 per year if you take an average COP of 3.0 for the air source then it will use 13300 KWH costing €1330 per year. But as heinbloed says it means nothing until you have a proper heatloss calculation and overall system design we are making a lot of assumptions on your heat generation and distribution here for there to be any degree of accuracy.

weston1

just checked plans there and the architect has a min average u value of 2.6W/m2K for a 383sqm house. would this make it easier to figure the right solution

Plombier

2.6W/m2K is very high for any part of a house except maybe windows. A U-Value is the measure of the rate of heat loss through a material. So a lower U-Value is better, the lower the U-value, the less heatloss your house will have. So if one type of window has an overal U-value of 1.5 and another has an overall U-value of 2.6. If your house has 100 msq of window at design conditions the better windows heatloss will be 3.75 KW per hour whereas the other will be 6.5 KW per hour.

heinbloed

Question from weston1:

just checked plans there and the architect has a min average u value of 2.6W/m2K for a 383sqm house. would this make it easier to figure the right solution

Easier, yes....
But what sort of heating system does the architect recommend?
Only a competent architect could figure out the thermal energy demand for your building, if he/she is competent to do that then certainly a recommendation on the most economival energy suply is available as well ?

Ask for it and we can dicuss it here.


PS

A

min average

does not exist. Either there is a Minimum or a Maximum or an Average U-value, a mix doesn't exist in such case....
Are you sure this is a competent person to be trusted with calculations ?