Supplement my heat pump with solar.

Wacked

I have a goethermal system with an nibe fighter heat pump. I am not that happy with it as my peak bill was over 600 for two months this winter. Granted it was a really cold winter and I have a lot of lighting. I was thinking of putting in solar panels to supplement the water heating . Does anyone know if this is practical. The good news is i have a lot of roof facing due south.

heinbloed

It can be done. What are you willing to pay for per kWh USED thermal energy ?

Wacked

I don't have a clue, I'm a layman who would rather pay now and save later. I don't know the ins and outs. I know now the heating system is pretty stupid as you cant chose when to heat the water, i.e heat the water at night rates.

RavenII

It can be done, but why would you be unhappy at 600 for all energy for two cold months? If you didn't have the heatpump, you might have had a €300 ESB bill, but then you would have used about €800 in oil on top of that! The payback of solar will be too long where the heatpump is in place - water heating is about 7% of your energy and you will need a very large solar array to integrate to the heating system. We had a similar bill too on a Nibe heatpump but it averages out at about €1400 for the whole year in 350m2 house.

saibhne

RavenII wrote: »

water heating is about 7% of your energy

Hi Raven. just wondering where you got this figure from? The only source I can find that talks about this is here. They go for 25% of fossil fuel energy consumption is used for water heating. Hot water specifically for showers and bathing etc.. would be a lower percentage than this alright but it would be great to find a verifiable source for this figure..

thanks,

S.

RavenII

saibhne wrote: »

Hi Raven. just wondering where you got this figure from? The only source I can find that talks about this is here. They go for 25% of fossil fuel energy consumption is used for water heating. Hot water specifically for showers and bathing etc.. would be a lower percentage than this alright but it would be great to find a verifiable source for this figure..

thanks,

S.

It would depend on the size of your house of course; adding solar will obviously drop your water heating costs, in a 3 bed semi it might be 25%...most 3 bed homes use about 20,000 kw hrs energy per year...water is usually 5,000-8,000. But if your house is double the size at 3,000sq ft, your water needs might still be the same.

saibhne

RavenII wrote: »

It would depend on the size of your house of course; adding solar will obviously drop your water heating costs, in a 3 bed semi it might be 25%...most 3 bed homes use about 20,000 kw hrs energy per year...water is usually 5,000-8,000. But if your house is double the size at 3,000sq ft, your water needs might still be the same.

Thanks but still not sure where you're getting the figures from?

RavenII

Bord Gais... used to quote the average 3 Bed at 18,000 kW Hrs consumption and 5,000 for HW in my previous career!

Pete_Cavan

Wacked wrote: »

I have a goethermal system with an nibe fighter heat pump. I am not that happy with it as my peak bill was over 600 for two months this winter. Granted it was a really cold winter and I have a lot of lighting. I was thinking of putting in solar panels to supplement the water heating . Does anyone know if this is practical. The good news is i have a lot of roof facing due south.

We have an air to water heat pump and towards the end of last year we had a new control panel installed which allows the cylinder to be heated at night and space heating is given priority during the day.Basically the system doesnt have to work as hard during the day to do both water and space heating. Of course that means we only have a cylinder of hot water to last us all day, but we have a combie boiler so that can heat cold water and deliver it to taps etc. (just means you have to wait a minute or two for water to be heated and make its way around the system to the tap).

We also had a weather compensator stat fitted outside which turns off the heat pump when temperature outside drops below three degrees. Air to water obviously takes heat from the air so when its cold outside it cant produce enough heat but it tries anyway, or did before the stat was fitted. It just means it does not waste electricity when it too cold to work. The combie boiler mentioned earlier takes over then and does everything. Not sure if the temperature stat would help with geothermal though, maybe it would if the pipes are not far below the surface.

Anyway, I presume you have a boiler as a backup system to the geothermal? Maybe installing a combie boiler and smaller cylinder (less water for heat pump to heat and combie taking care of any additional hot water needs) would reduce the cost. Of course then you have the extra cost of gas/oil for the combie boiler but Im sure the most efficient system would be to combine the advantages of both renewable and fossil fuel.

RavenII

Sounds like a funny control strategy...the Nibe heatpump only runs hotter when water heating is required; then it just produces the necessary level of heat calculated on outside temperature - not the same as a weather compensater / valve. You can also program the hot water to be off during the day and the level of heat to drop a little during peak periods or even increase and stash extra energy in the concrete slab. On top of that you can text the machine to alter any of the settings with a little Nibe gadget we just got. Generally speaking (unless your house is huge and you can't get II phase ESB) you wont need oil or gas with geothermal, but only to supplement an air to water system

PeteHeat

Hi,

The courses I did on heat pumps both Geothermal and Air recommend the systems should be bi-valent (as described by Pete_Cavan).

Heat pumps are designed to work best at pre-determined source temperatures it is how the COP is calculated, assuming the flow temperature does not change air to water is more effecient with higher air temperatures than colder air temperatures.

To avoid oversizing the heat pump a back up source of energy is recommended by most reputable manufacturers, our air temperatures are both cold and moist.

I have walked around continental cities in a cardigan (trousers were also a help) with temperatures at -5c and felt it was a crisp night instead of the bitter cold we feel here at the same temperatures.

Wind chill does play an important part in how efficient any air to water heat pump will perform, with ground source / geothermal it is important to ensure the right soil conditions and depth to ensure there is sufficient re-charge.

One of the big mistakes with ground source / geothermal is not insulating the flow and return pipes in the ground where they pass each other, another is not having the pipes deep enough.

Depending on the size of the system and house the OP is trying to heat solar may help as a pre-heat in a low temperature system, the reliability of the amount of energy the solar can collect in winter would be a concern, also what to do with the excess heat generated in summer could be another issue.

There are too many variables and not enough information to give an accurate answer on the solar, bivalent is recommended.

.

RavenII

If you live in Sweden or Germany etc it would need to handle peak loads of -18°C etc....in our short mild winters you don't necessarilly need back-up (or Bivalent as you call it) unless your house is above a certain size and you only have a single phase supply.

Damp climate has absolutley no adverse effect on an air/water machine; in fact damp air contains more energy, and for geo we have higher ground temperatures, thanks to rain etc

The COP (Coefficient of Operating Performance) is not a calculation - its the resultant running conditions - temperature in / influencing temperature out. Temp. in Ireland averages about 7° on our geothermal unit, so we simply enjoy higher COP's.

But back to the original question - you can supplement the heatpump with solar. No problem - two ways 1. just do the hot water. 2. HW & heating support...technically no problem . The payback period is just too long in retrofit situation.

PeteHeat

Hi,

Ground temperatures are one thing, factor in wind chill and the figures are different or so the Met office have us believe, of course walk outside any cold night and we figure that out for ourselves.

Cold Moist Air definitely has an effect on air to water heat pumps, if it didn't why do the manufacturers include anti freezing measures in the design and programming ?

The majority of Irish homes have single phase electricity, three phase would be very unusual as it can be very expensive to get the ESB supply, so the heat pumps (both air and ground) tend to be the smaller output which is why bivalent is often necessary.

An air to water system in identical houses one in the south and the other in the north will perform differently as the air temperatures (fuel supply) on average are different.

A constant 7c is good which suggests your site conditions were suitable and your loop is deep enough so you have good recharge which comes from ground water, rain and sun.

COP is changing all the time with air, ground, flow and return temperatures I agree.

One of the problems experienced by many is they were told they would have a COP as high as 4.5 when buying the system, some in the business were leaving out the variables some of which are nature and heating system controls.

If the OP has a buffer which some heat pumps do, it may be possible to add a heat exchanger for the solar contribution.

Removing the heating of water for sanitary use will remove the need for the heat pump to reach maximum flow temperatures allowing it to perform at the constant low temperature for the heating circuits.

Nothing can be ruled in or out without knowing more about the system.

.