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Author Topic: Heat Pump in the Loft?  (Read 10436 times)
unclefester
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« on: January 20, 2015, 10:19:06 PM »

Hello there

New to all this so if I'm being daft be gentle. Having recently installed a heat pump to a small pool used for canine hydrotherapy work I am very impressed with the efficiency and cost savings over the old electric water heater.

This has got me thinking - the house is a bungalow with oil fired central heating and a multi fuel stove (stockton 8 ) one end gets lovely and toasty but the other end, our bedroom resembles a chiller in winter. I had explored the possibility of running some air ducting through the attic space from one end to the other (15m) but the heat loss over the distance seemed to make it fairly pointless would a small heat pump with the "outdoor" bit up in the loft near the chimney breast and the indoor bit sited in the bedroom make sense?

Thanks in advance

Geoff
« Last Edit: January 20, 2015, 10:39:29 PM by unclefester » Logged
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« Reply #1 on: January 20, 2015, 10:27:52 PM »

Hallo Geoff, welcome.

not really a good idea in my view, all you would achieve is to make the loft space colder thus increasing the rate that heat would leak from your rooms to the loft. Much better to place the "outdoor" exchanger in a sunny spot outside with good air circulation all around it.

Desp
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mike7
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« Reply #2 on: January 21, 2015, 12:04:42 AM »

I don't think it's altogether a daft idea, especially if the heatpump is small and the attic is big. If your attic floor/bedroom ceiling is well insulated and the attic roof isn't, then the extra heat loss due to the lower attic temp won't be much. Also, if the attic is fairly airtight, then there could be an advantage when temp drops to a level where the heat exchanger would start to frost up if outside. With a low rate of airchange in the attic the air would get dehumidified once and then accumulate frost at a lower rate, thus spending less time on defrost cycles than if it were outside.
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RIT
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« Reply #3 on: January 21, 2015, 12:58:32 AM »

Putting a standard air based unit in the loft would be a very bad idea. The main reason being will be the build up of heat/cold in the loft as there will be no real airflow. The reason for the very large fan on a condensing unit is due to the high volume of air that has to pass though the unit per min. In the summer you are trying to dump heat via the condenser(cooling hot coolant) and in the winter you are trying to use external ambient heat to move the 'cold' outside (by warming the coolant). In an enclosed space like a loft you would be raising the overall ambient temp up to a point where the condenser can no longer operate in the summer and in the winter you would remove all the ambient heat and so again the condenser would not operate. The result maybe that the condenser stops or you end up with a COP*/EER** of 1 (or less), so for every 1KWh of energy you put in you get at most 1KWh of heating/cooling.

Also you are unlikely to have enough sound proofing to deal with placing the condenser above your heads, these units are normally around 50dB(A)+



*COP the  ratio that measures the energy efficiency of the HEATING performance.
**EER the ratio that measure the energy efficiency of the COOLING performance.

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Nickel2
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« Reply #4 on: January 21, 2015, 09:05:32 AM »

I have been thinking about a small heat-recovery unit to fit in the loft-void of my workshop. For 5 months of the year the space can reach up to 55c. Above that, it becomes self-regulating and the roof re-radiates the heat. I had a plan to run a small air to water heat exchanger,  (car interior heater matrix, low current, solar operated fan), in the void, with the cold end of a 6mm Hep2O circuit buried somewhere in the cold bottom of the thermal store, contributing to the overall DHW temp. This would stop the workshop getting boiling in the summer. It would be switched off when the temp in the void falls below 25c.
Like RIT says, a commercial unit would be noisy expensive and uneconomical, but for the bodgineer, it's more energyto be harvested.

Substitute 'roof-void' for 'hot room'; substitute 'cold bottom of thermal store ' for 'chilly bedroom'.

If your misses doesn't moan about it, it's win-win.
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unclefester
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« Reply #5 on: January 21, 2015, 02:43:30 PM »

To clarify things a little - heat leaking from the rooms to the loft would not be a problem once the log burner is fired up the temperature goes through the roof rapidly at that end of the house a bit cooler would be a blessing. Also the possibility of the "outside" unit not being able to dump the heat isn't really an issue as I really don't want to use the unit for air con purposes in summer so it would be turned off throughout anyway. I  just want a way of transferring excess heat from one end of the house to the other (15m).
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Blodders
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« Reply #6 on: January 21, 2015, 02:54:49 PM »

So, in essence, you currently have one room too hot and another, 15m away, too cold.

I would venture to suggest that there are far better ways to resolve this than to rely on the excess heat passing through your loft insulation to the attic, then being used to boil refrigerant which in, turn is pumped to the other end of the house where it gives up that heat to warm another room.

For example, can the Stockton 8 be retrofitted with a boiler to run a couple of rads? Even simpler might be to just duct warm air from the hot room to the cold room with an inline fan.

A heatpump in the attic is effectively turning your attic into a fridge. The increased DeltaT between warm room and attic will mean greater heat loss from there to the attic, that may increase comfort in the warm room but at a cost of burning more fuel. And using electricity to move that heat from the now warm attic to the cold room.
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Andyr
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« Reply #7 on: January 21, 2015, 03:17:39 PM »

I've just installed a MHVR system in my loft. This is MUCH quieter than the unit you propose. Yet directly above it we can still hear it slightly. That's after taking care of how its mounted etc. So no way would I ever consider a heat pump in the loft risking some sleepless nights and with all that stopping and starting. Unless of course you can put it a long way away from the bedrooms. What about condensation risk with a cool loft on a humid day?

Andy
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mike7
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« Reply #8 on: January 21, 2015, 05:52:14 PM »

I wouldn't abandon the idea yet - small aircon units are cheap to buy and amenable to DIY installation, so the outlay could easily be lower than for example the stove mod/radiator suggestion ( which may also lower the efficiency and clean burning of your wbs). They are very quiet, especially the delivery end where you're sleeping, and because they modulate there is little switching on and off. People here may be thinking of larger output monoblock HPs which have tended to be noisier, and not modulating. A unit rated at 2kW (they seem generally to be rated on their cooling capacity) should give a rated heating capacity in the region of 2.5 or 3kW, which should be loads for your bedroom. Whether it would turn your attic into a fridge depends on the area and U-value of the attic roof, and how well ventilated it is. If your answers to these questions are the same as they are for my situation, ie 'big', 'huge' and 'fairly' then the degree of chill involved is going to be slight. Perhaps worth mentioning also that assuming a COP of 3, one third of your bedroom heat will be provided by electricity, just 2/3 extracted from the attic air.

I assume you're not on mains gas, in which case the economic argument for having a small AAHP is very strong regardless of where you put the 'outside' bit - unless perhaps the recent international oil price drop has pro rata worked its way through to heating oil. flyingpig
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Countrypaul
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« Reply #9 on: January 21, 2015, 10:46:27 PM »

Given that you want to move heat from one end of the house to the other why not just use a smaller aircon unit with the cooler where the stove is and the heater in the bedroom? This would surely be far more efficient in terms of gathering the heat avoiding condensation etc. The main issue would be can you easily run the pipes from one end of the house to the other?
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RIT
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« Reply #10 on: January 22, 2015, 01:18:18 AM »

I wouldn't abandon the idea yet - small aircon units are cheap to buy and amenable to DIY installation, so the outlay could easily be lower than for example the stove mod/radiator suggestion ( which may also lower the efficiency and clean burning of your wbs). They are very quiet, especially the delivery end where you're sleeping, and because they modulate there is little switching on and off. People here may be thinking of larger output monoblock HPs which have tended to be noisier, and not modulating. A unit rated at 2kW (they seem generally to be rated on their cooling capacity) should give a rated heating capacity in the region of 2.5 or 3kW, which should be loads for your bedroom. Whether it would turn your attic into a fridge depends on the area and U-value of the attic roof, and how well ventilated it is. If your answers to these questions are the same as they are for my situation, ie 'big', 'huge' and 'fairly' then the degree of chill involved is going to be slight. Perhaps worth mentioning also that assuming a COP of 3, one third of your bedroom heat will be provided by electricity, just 2/3 extracted from the attic air.

I assume you're not on mains gas, in which case the economic argument for having a small AAHP is very strong regardless of where you put the 'outside' bit - unless perhaps the recent international oil price drop has pro rata worked its way through to heating oil. flyingpig

My comments were based on the use of a small split Inverter based unit, mainly because its something I've looked at in the past as I have no easy way to install the outdoor unit on my outside wall. This does result in a low noise internal unit, the best I've found is rated at 23dB(A), but the unit going in the loft is rated at 50 dB(A). Now how loud that is will depend on where you live. If you live near a motorway you may not notice, but otherwise its a lot of background noise.

The issue is the loft space would have to be 'very' well ventilated, when using a 1kW unit in the summer to provide around 3kW of cooling you will be trying to dump 3kW of heat into the loft space and as the loft temperature increases the COP will drop. There is an easy way to tell just how ventilated a loft is, just check its temperature on a nice sunny day and compare it to the temperature in a open shaded area. For my house the loft temperature is often around the operating max ambient of the smaller DIY systems (around 40c). The same problem happens in the winter as you try to extract heat from the available air, again the low cost systems often have a rather high requirement for the ambient air temperature (around -5c). The problem is that air has a very low specific heat capacity, so it can not provide or accept much heat, hence the large high air flow fan in the condenser. It takes over 4m3 of air to match the same heat capacity of 1kg/l of water.


If the situation is that the aim is to move heat around as others have noted a basic heat recovery unit would be far cheaper and allow heat to be extracted from the hot room and moved (via the loft and ducting) to the cold room. A basic unit such as the MANROSE HR100R (which I found via some web searching) is around 210 and has a maximum power consumption of 30W. As noted by Blodders this could be made even cheaper if you installed an in-line ducting fan (maybe 40-90). The advantage of the heat recovery unit is that you will be warming fresh air, rather than moving air from one room to another.



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« Reply #11 on: January 22, 2015, 10:04:25 AM »

There are 3 things you really need: Insulation, insulation and more insulation. Don't forget warm clothes in the winter.

Unless you have insulated cavity filled walls, Grade A windows and doors, 300m plus of loft insulation, NO tumble dryer, Grade A appliances, Solar Thermal hot water, passive shading in the summer, all drafts sealed.....its daft using a heat pump to balance room temperatures, its just another way to waste more electricity.

If the house is very well insulated it will feel comfortable everywhere. We noticed significant benefit when we had Grade A windows and front door fitted. U value about 1.5 !!

-Paul
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« Reply #12 on: January 22, 2015, 10:09:42 AM »

I've just installed a MHVR system in my loft. This is MUCH quieter than the unit you propose.

Also dramatically less power consumption, from 2000+ Watts down to about 35 Watts, depending on fan speed.

Well done Andy, any pics? MHVR is on my bucket list.  Smiley

-Paul
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« Reply #13 on: January 22, 2015, 03:39:45 PM »

The only pic handy it was cheapish but does the job .... note the carpet underlay layers to stop sound traveling down from where it sits. Heading slightly off topic...


* HRV1.jpg (299.57 KB, 1200x674 - viewed 1275 times.)
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« Reply #14 on: January 22, 2015, 03:43:13 PM »

If you want to help stop noise transmission, hanging it from bungees is good..........
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