Heat Pump & Night Rate Meter - a no brainer?

KCross

Metric Tensor wrote: »

Thanks for the info lads. I don't disagree with anything there.

Personally I don't think I'd be too happy for a standard heat curve based in an average of all houses to decide my heating profile without taking into account the specifics of the dwelling, exposed areas, volume, ventilation rate, screed depth, etc. But maybe if there is sufficient scope to adjust the heat curve that can be overcome.

Three questions if that's OK:
1. Are the heat curves user adjustable?
2. Did you find the absence of zoning caused problems with your DEAP calc?
3. Is there any internal stat at all? I would have thought that having one in conjunction with the external stat would have greatly aided the system. But I suppose if the assumption is that it is always X degrees inside the manufacturers may be happy with that.

1. Yes, user adjustable
3. Yes, but only for user info, it doesnt control the HP.

BarneyMc

Water John wrote: »

Otherwise revert to what we built 25 years ago. One system no zones. I thought we had moved a good bit from that?

As we move to higher spec houses zoning has become less important, i.e. open plan areas and none of the "close that bloody door" thinking. A house that hold heat well should not rely on so much on zones and should sit at a comfortable temp throughout.

JimmyMW

Water John wrote: »

Why would anyone want bedrooms at 21c? Lots of savings and better living conditions by having them at 18c. That could be 40% of the house. Also with individual stats, bedrooms not being used could be turned down further 16c or turned off.

Unless you have a thermal break between your bedrooms and the rest of the house all you are doing is making the 60% of the floor that is active work harder to heat 100% of the space, this is the total wrong type of thinking for heat pump technology.

Metric Tensor

I've been thinking about this since. In a two storey house with no internal zoning or thermostat is there not a danger of totally different heating behaviour upstairs and downstairs with the heatpump aggregating the return temperature and not accounting for the effect of the downstairs rising heat on upstairs?

Water John

With UFH the floor of each room should be insulated all round, no bridging.
Yes all the house needs to be comfortable, but that means different temp in different areas of the house.
Don't understand what is meant by saying this doesn't suit HP. You are holding the temp stable with the heat sink of the 75mm slab.
The only point I would see is to avoid as much as possible the HP cutting in and out often.

JimmyMW

Water John wrote: »

With UFH the floor of each room should be insulated all round, no bridging.
Yes all the house needs to be comfortable, but that means different temp in different areas of the house.
Don't understand what is meant by saying this doesn't suit HP. You are holding the temp stable with the heat sink of the 75mm slab.
The only point I would see is to avoid as much as possible the HP cutting in and out often.

And do you have the walls between the bedrooms and the rest of the house insulated also?

Water John

If you don't have stats you end up as Metric above asks with very warm bedrooms. A difference of 3c between a bedroom and living area, wont lead to dramatic heat loss via the dividing wall. The two spaces will attempt to equalise, but very little and inconsequential.
However the house will be more comfortable and cost little less to heat.

JimmyMW

Water John wrote: »

Why would anyone want bedrooms at 21c? Lots of savings and better living conditions by having them at 18c. That could be 40% of the house. Also with individual stats, bedrooms not being used could be turned down further 16c or turned off.

Water John wrote: »

If you don't have stats you end up as Metric above asks with very warm bedrooms. A difference of 3c between a bedroom and living area, wont lead to dramatic heat loss via the dividing wall. The two spaces will attempt to equalise, but very little and inconsequential.
However the house will be more comfortable and cost little less to heat.

Turning the rooms off will result in more than a 3c difference, read your post above. Anyway as said in other posts, you can set the heat to vary during different parts of the day, 18c is required in bedrooms for sleeping, therefore in most cases 18c is required at night only. The whole house should drop in temp together at night and heat up during the day. With your methodology why bother heating bathrooms etc?

Water John

Well Jimmy we'll just agree to differ.
Not in the business anymore but spent 5 years on UFH house design.
Just don't understand over heating parts of the house.
Just to be accurate, one could normally run the bathroom at 21c, governed by the living area stat. Some would prefer to use an external stat with a probe and thus have it at 23c.
That would be a clients choice.

water-man

Metric Tensor wrote: »

I've been thinking about this since. In a two storey house with no internal zoning or thermostat is there not a danger of totally different heating behaviour upstairs and downstairs with the heatpump aggregating the return temperature and not accounting for the effect of the downstairs rising heat on upstairs?

What I have found is that the whole house is the one comfortable temp 24/7. Every room is the same. Its not like older houses I've lived in where the room with the fire is roasting and another room can be a lot cooler.

An example my sun room which is south facing can get a lot warmer through solar gain than the room pointing north. But this too is averaged out as our house is very open plan and the other doors are open so the air is always circulating (helped by MHRV) so what you end up with is a "natural" temperature balance (helped by being well insulated and air tight).

WM

ecowise

A few observations:
We have been running our GSHP with UFH upstairs and downstairs since Dec 2001 and have found zones effective and economical. Our heating cost so far this season for a 250 m2 house is €130 operating at night rate only (we supplement with our wood stove as needed using our own logs). If I was building again now I would build to a higher spec and rely on a MHRV (or possibly passive HRV) supplemented again with a log stove.

As to the discussion regarding the use of ASHPs at night it should be noted that (in my case anyway):
night rate starts at 23:00 hrs and ends at 08:00 hrs (advance for one hour for summer time).
The sun sets much earlier i.e. night time weather wise begins around 5pm (while on the day time rate) so a good chunk of the day time rate is actually for nighttime!

Also the temperature difference between night and day during the winter is not very big on average in our climate. It is not unusual for the temperature to rise during the night during the winter such as when a mild & damp weather system moves in from the SW after dark.

I did a simple calculation based on my weather station (west Waterford) for the months Oct-Mar inclusive and compared the average temperature for the night rate period (2300-0800h) to the average for the day rate period (0800-2300h) (making no allowance for clock change which would be very small) and calculated a night rate period average temp of 6.4 degrees C and a day rate period average temperature of 8 degrees C. Therefore operating at night only would not result in a significant performance penalty.

The problem that I have encountered with thermal modelling of houses is that the only way to do it properly is with a physics based simulation engine and that takes a lot of time to set up.

Water John

Excellent post, Ecowise.