Simply sizing a heat pump for a heating load and assuming it will cope with summer cooling load conditions is no longer an acceptable practice.
Geographical locations that experience ambient temperatures above 30oC on a regular basis are common as well as high night time humidity associated with some areas of Auckland. High humidity combined with solar and radiant daytime heat gain can make sleeping uncomfortable.
Heat pumps always produce more heat output than cooling output.
This is purely physics when a reverse cycle heat pump is heating the “heat of compression” electrical energy and friction heat is added to the useful delivered total heat delivered to the space. Where as in the cooling function it is rejected via the outdoor condenser cool.
Sizing a heat pump for cooling or air conditioning needs to take into account the following factors:
- Outdoor and Indoor ambient design condition
- Direct solar radiation
- Transmission load
- Ventilation and infiltration rates
- Internal load heat load
Solar heat gain from glass windows and atrium areas can be as high a 700watts per square metre depending on the type of glass and the sun incidence angle.
Competent air conditioning companies will allow for these factors when sizing heat pumps for cooling.
A rule of thumb that can be applied as a check is 1.3 times the heating load calculation.
Always check with your supplier when purchasing a heat pump for cooling requirements that the above factors have been considered.
June 8, 2010 at 11:36 am
Hi Peter,
i was wondering if you have any info on the amount of moisture generated in a standard kitchen (gas or electric cooking) and if you knew of guidelines for the removal of that moisture in the room. I have a client who is considering not installing a rangehood and wondered if that’s OK when combined with any of your ventilation systems.
Many thanks, Toni Roberts, kitchen architect designer
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June 10, 2010 at 9:12 am
Would like to know if having an HRV or DVS system installed in your home is actually beneficial for keeping ones house dry and warm. Dose it really work like they say it does?
Does one need to have the correct amount of pink batts, wall ceiling, and double glazed windows, for it to work properly?
Thank you
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June 10, 2010 at 2:37 pm
Hi,
i am looking at doing a fitout for a Florist/giftshop in an internal space within a commercial building. The plants etc obviously always need to be cool and not get too dried out. Is there a certain type/size of Airconditioning unit for this type of space you would recommend? the space is only approx 30sqm.
Thanks.
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June 10, 2010 at 3:08 pm
Hi Peter,
What are the determining criteria and factors when deciding between using one large heat pump and multiple consoles/panels in different rooms or multiple separate units for each room please ?
Hans Mitt Architectural Design
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June 11, 2010 at 8:55 am
Peter
when looking for the best option for heat pumps and the size (kw rating) you require for a standard 4 bedroom home 2 bathroom around 220sq mt
what do you believe is the better unit
the floor mounted or wall mounted
im still very much in the dark when it comes to the better model required
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June 11, 2010 at 9:43 am
Dear Peter. Thank you for an informative article. I have a few questions, relating to sizing, for well built highly insulated homes. We’re building homes, routinely, with R3 in the walls and R4 in the ceilings, or R2.6 in the walls, R3.2 in the ceilings, and N50 standard. N50 standard is where we add a special layer in the construction and do a home air leakage test and the aim is to reduce the standard 7-10 forced air changes / hour to no more than 1.5 forced air changes per hour. This would mean that our leakage rate (which is shown as 10% Infiltration above), will theoretically reduce significantly. What I’m hoping to achieve is some factor so that I can write into my specifications: “By achieving N50 standard the heat-pump unit sizing can be reduced by a factor of …..%.” Any suggestions?
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June 11, 2010 at 12:13 pm
Hi Peter,
I have a client who is keen on passive solar heating, I am looking at ducting air from a sunny external insulated wall with a cavity through the wall into the interior. The issue I have is controlling the open+shutting of a damper + possibly fan. Are there off the shelf units that can be set to only open when there inside room is under 20deg + the cavity is over 20deg? BRANZ did some work on this + called them solar walls, they used a water cylinder thermostat + 2 sensors, it just seemed a little ad-hok. Any help would be appreciated. Thanks
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June 14, 2010 at 2:45 pm
Hi I have a two story house am I best to put my heat pump upstairs or down. We have bedrooms downstairs that need to be warm(ed) thanks Rick
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June 24, 2010 at 4:59 pm
Hi, Is it false economy to duct hot air from the room with the heat pump to another part of the house or put another source of heat in that part of the house.
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