GSHP for cooling - Hot climate area

[Shah]

Hello All,

 

As per the title, can a ground source heat pump be used for cooling in an area where climate is hot most of the year (around 8-9 months).

Can a single borehole be enough to support such a system?

Is there a software which can be used to see how much cooling requirements for a house plus design a cooling system accordingly?

How efficient such a system would be compared to a conventional air conditioning say if the inside house temperature is maintained at around 27-28 Celsius compared to outside of 45-50 Celsius?

Would under floor cooling work?

 

Thanks,

Shah.

 

[jack]

If it's that hot, I assume there's lots of solar energy available. Given the cost of installing and maintaining a GSHP system, you're probably better off with a decent photovoltaic array driving an air conditioning system (and/or perhaps using underfloor cooling - if it's regularly into the 40s, I suspect underfloor cooling will make things feel a lot more pleasant).

[Shah]

Thank you Jack,

Yes lots of solar energy available but the problem is it is only during the day. At around 15p/kwh the electricity bill would stack up very quickly. The temperature during summer months will fluctuate between 35-50C (Mid March to Mid September). Peak temperature is during May and June which will be around 45-50C consistently during the day and around 35-40C during night time. During July-August it is very humid and hot still around 35-40C. March, April and September, October have cooler nights so ceiling fans can do the trick.

I checked the ground water temperature was at around 29C. So was thinking about heat pump in reverse cycle.... Borehole cost would not be much (far lower than what is paid in UK).

Can a passive house be built with very good air tightness in order to keep the climate reasonable controlled. Windows with shutters/overhangs (outside). Not sure on insulation levels...

Edited June 30, 2017 by Shah

[ragg987]

I suspect humidity will be a key factor here - cooling via a slab will drop the temperature but not remove moisture in the air. I am guessing that you would have condensation issues in that case as relative humidity will increase as room temperature drops.

 

An air-to-air heat pump (i.e. the ubiquitous aircon) will remove moisture and drop humidity, contributing to the comfort.

 

I lived in Singapore for a period and it amazed me how poorly the buildings were constructed. Single glazing and non-existent air tightness, so aircon was always on and switching it off resulted in a warm room relatively quickly, though the solid concrete floors that are the norm would retain some coolth for a while. I also preferred the split units as they were much quieter - the noisy HP can be hidden away outside.

 

I see no reason why a PH standard would not work well, provided you can get your architect and builder to embrace and follow through with it with diligence. And then maybe use a cooling strategy that takes advantage of solar PV - cooling on while the sun shines then switch off after and let the PH do it's bit and retain the cool through the night.

[jack]

If you have good insulation and airtightness, I think you'd be fine not running the cooling overnight. If the slab and air temp is kept in the high teens or low 20s during the day (or whatever temperature is needed to keep condensation at bay), it shouldn't get that much hotter overnight.

 

In that sort of climate I'd also definitely consider underfloor cooling upstairs (and maybe even cooling of some internal walls). That will tend to keep the temperature more stable throughout the house.

 

You're right to try and control solar gain.  Basically your scenario is about as extreme as it gets, so I'd be using every available technique to keep the heat out, and the cool in.

 

By definition, the Passivhaus standard requires high levels of insulation.  Bear in mind, though, that where you have several months during which temperatures are permanently well above comfort levels, no amount of insulation will keep you cool forever - serious active cooling is absolutely going to be a requirement.  My preference in this situation would be slab cooling, with aircon to keep humidity levels down.

 

(Actually, my preference would be to move somewhere cold, as I can't stand the heat. I'd never, ever leave the house if I lived somewhere that regularly topped 40 C!)

[Shah]

36 minutes ago, ragg987 said:

I suspect humidity will be a key factor here - cooling via a slab will drop the temperature but not remove moisture in the air. I am guessing that you would have condensation issues in that case as relative humidity will increase as room temperature drops.

 

27 minutes ago, jack said:

If you have good insulation and airtightness, I think you'd be fine not running the cooling overnight. If the slab and air temp is kept in the high teens or low 20s during the day (or whatever temperature is needed to keep condensation at bay), it shouldn't get that much hotter overnight.

 

So ground floor and first floor slab to be cooled by a heat pump or some other means? If both slabs kept at around low 20s during the day while run on a PV array. Plus have a conventional air conditioning for humidity control? A mechanical ventilation system for the whole house?

Good air tightness can be achieved plus insulation in walls and roof etc. Windows will be problematic but hopefully good air tightness can be achieved. Also probably try to keep the glazing to minimum.

49 minutes ago, ragg987 said:

I lived in Singapore for a period and it amazed me how poorly the buildings were constructed. Single glazing and non-existent air tightness, so aircon was always on and switching it off resulted in a warm room relatively quickly

That is the situation right now. No air tightness/insulation and single glazing. So was thinking how much difference could an air tight/insulated house with double glazing (plus exterior shutters) make to comfort levels as well as electricity bill. Is there a software I could use to see how much cooling will be needed etc?

 

44 minutes ago, jack said:

(Actually, my preference would be to move somewhere cold, as I can't stand the heat. I'd never, ever leave the house if I lived somewhere that regularly topped 40 C!)

Well that is another way of getting rid of a problem

[ragg987]

My approach would be:

 

Priority 1: mitigate the issues ("fabric-first")

Shutters are a tried-and-tested solution to reducing solar gain, so if you have East / West glazing consider these.

Insulation to a high standard - roof, walls, floor

Double or triple glazing

Attention to air-tightness in all fabric elements, including well sealing external doors and windows.

I suspect light-coloured external walls will reduce the heat gain as well.

 

Once the mitigation is in place, then consider how to reduce heat and humidity. You should be able to model the heat gain using some of the spreadsheets available - e.g. @JSHarris has one, I believe (have not tried it myself, we did a PHPP calculation). This will give you an indication of the power you need - say 10kW with external temperature of 50C and internal of 25C. Don't forget to add heat generated internally to the equation - people, cooking, showers etc. In Northern hemisphere these are a good thing, in your case the heat added needs to be removed.

 

You now need to provide a cooling power to match that - 10kW (plus some extra for safety). Say 15kW. This becomes the size of your heat pump(s).

 

I would be inclined to go with A2A split air conditioners - these are readily available and cheap in most hot countries, spares and repairs will be easy vs importing a GSHP that no one can support and spares have to be imported. E.g. a large heat pump (or 2) outside and internally have small fan units in all the rooms. These cool and remove humidity - both are essential for comfort. Use of the aircon for extended periods (e.g. 12 hrs per day) will cool the room as well as the fabric inside of the insulation - so it should cool the floors and internal wall, plus furniture and so on. These store the coolth and release it into the building when you switch off the aircon.

 

Then comes the question of powering the aircon - Solar PV is the obvious option, drive the aircon during the day and switch off at night.

 

You will need to factor in DHW - perhaps Solar PV as well? insulate your DHW tank and pipework well else you are increasing the heat load in the house.

 

And finally, think about air-changes. Your aircon will remove humidity but will not provide fresh air, so potentially a MVHR. I suggest you speak to the MVHR suppliers about this - most on this forum use it to warm the outside cold air before it comes into the house, you want to do the reverse, not sure what this means to e.g. condensation at the heat exchanger.

 

[jack]

46 minutes ago, Shah said:

So ground floor and first floor slab to be cooled by a heat pump or some other means? If both slabs kept at around low 20s during the day while run on a PV array. Plus have a conventional air conditioning for humidity control? A mechanical ventilation system for the whole house?

 

Yes to all those things.

 

Worth doing some modelling though. We're used to dealing with moderately cold winters and mostly mild summers in the UK. The sort of climate you're talking about is a huge extreme in the other direction. You might, for example, need to consider how to deal with moisture movement within the structure. The interior will be cooler and lower humidity than the outside. This might mean taking a different approach to vapour control than we'd take in the UK.

[Shah]

Thank you @ragg987 and @jack

 

Did a bit more reading

On ‎30‎/‎06‎/‎2017 at 13:15, ragg987 said:

I would be inclined to go with A2A split air conditioners - these are readily available and cheap in most hot countries, spares and repairs will be easy vs importing a GSHP that no one can support and spares have to be imported.

I was thinking the same. So what is the difference between an Inverter AC and A2A Heat Pump or they are the same?

 

On ‎30‎/‎06‎/‎2017 at 13:15, ragg987 said:

You will need to factor in DHW - perhaps Solar PV as well? insulate your DHW tank and pipework well else you are increasing the heat load in the house.

Well much of the year this won't be needed and for the couple of months it will be needed a gas boiler can be used.

 

On ‎30‎/‎06‎/‎2017 at 13:15, ragg987 said:

And finally, think about air-changes. Your aircon will remove humidity but will not provide fresh air, so potentially a MVHR

Yes this is my main concern as the air is not replaced and also some nights/days when it rains the outside weather is very cool and would like a passive/active system which could replace the internal air with fresh air.

 

On ‎30‎/‎06‎/‎2017 at 13:16, jack said:

You might, for example, need to consider how to deal with moisture movement within the structure. The interior will be cooler and lower humidity than the outside. This might mean taking a different approach to vapour control than we'd take in the UK.

Yes good point. I also thought about running day time temperatures around 20C would make it uncomfortable during the day as it will be too cold (here we are talking about almost 25-30C difference from the outside temperature).