ceiling air conditioner

Mar 2, 2010 at 07:07 o\clock

How to buy a heat pump system?

by: zhonglv   Keywords: heat, pump

A heat pump is essentially an air conditioner that can both heat and cool a house. A simple explanation is that a heat pump can extract heat found in the air (or ground) outside your house and transfer that heat into your house instead. Under the right conditions it can do this substantially more cheaply than a gas or oil furnace.

Consider the following questions when buying a heat pump:

·      Is a heat pump the best choice — or would you be better off buying a furnace and a central air conditioner?

·      What size heat pump should you buy?

·      What is heat pump efficiency, and how efficient should your heat pump be?

·      Which brand of heat pump is best?

·      Who should install your heat pump?

  Is a Heat Pump the Best Choice?

   Since heat pumps can both heat and cool a house, wouldn’t you always rather buy a heat pump than a central air conditioner? And wouldn’t you rather have a single piece of equipment to purchase, install and maintain than both a central air conditioner and a furnace? While the answer may be this simple, you should consider several factors.

   The seasonal weather in your region is probably the most important factor in this decision. If the temperature rarely dips below 40 degrees Fahrenheit, you can probably heat your home more affordably with a heat pump than a furnace. However, if the temperature is often colder, you should consider having a backup heat source. Many people choose a gas or oil furnace to serve this purpose — both for reasons of cost and because a furnace can more easily maintain warm temperatures when the difference between the temperature outside and inside increases.

   Second, heat pumps are generally more expensive than a central Ceiling air conditioner of the same efficiency and capacity. For example, at one direct-to-consumer retailer, a 1.5 ton, 13 SEER Rheem heat pump retails for about $100 more than the equivalent 1.5 ton, 13 SEER Rheem central air conditioner. Contractors may also charge more to install a heat pump than a central air conditioner.

A third criteria to consider is longevity. Since a central air conditioner is typically only used during the summer months, and a heat pump is used during both summer AND winter, the lifespan of a heat pump is typically shorter than that of a central air conditioner. Maintenance costs are typically higher as well, since the compressor, controls and other components will run more months out of the year.

   Finally, natural gas and oil have historically been more affortable than electricity. However, as petroleum costs have skyrocketed in the past months, this may not be true in your area. ( Of course, this also varies by region. Some, for example, have pointed out that the many hydroelectric dams in the Pacific Northwest of the United States often result in electricity costs lower than natural gas costs.) Since heat pumps almost often run on electricity, you’ll want to consider whether a gas furnace would be cheaper.

  What size heat pump should you buy?

   Choosing a heat pump that outputs the correct amount of warm and cold air ensures comfort, low maintenance, and efficient operation. Heat pumps should be sized to run continuously to maximize efficiency. A heat pump that is too large for your house cycles on and off too often, which increases the wear on the equipment and decreases its efficiency. Too small, and the unit may not be able to keep you comfortable during both summer and winter.

Unfortunately, there is no shortcut to an accurate measurement — you need to get an HVAC contractor to calculate your house’s heating load. The standard measure of a heating load is a Manual J calculation, and it takes into account your house’s insulation, size, amount of shade, and many other factors.

  Heat Pump Efficiency: SEER vs. HSPF

   The heating and cooling functions of a heat pump each have their own measure of efficiency. A heat pump’s cooling efficiency is measured by its “Seasonal Energy Efficiency Rating”, or SEER. Its heating efficiency is measured by its “Heating Seasonal Performance Factor” or HSPF.

   In warm climates where you’ll want to generate cool air often and hot air rarely, you’ll want to choose a heat pump with a high SEER. In cooler climates, you’ll want to make sure that your heat pump has a high HSPF.

Highly efficient heat pumps typically cost more than less efficient models. You may want to consider how many months it will take to pay off this increased cost through savings in your energy bill. If you are planning to leave your current house within a few years, you might prefer to install a lower efficiency heat pump, as you are unlikely to recoup the extra cost. (Of course, money is not the only factor to consider — you may be willing to pay more to reduce your house’s impact on the environment.)

  Who should install your Heat Pump?

   One of the most important choices you will make in buying a heat pump is which contractor to hire. A good contractor will correctly size your heat pump, help you calculate the payback period of high and low-efficiency equipment, and ensure that the equipment is installed properly. In addition, they will respond promptly when you have an HVAC crisis, provide ongoing maintenance, and act as a go-between with the manufacturer to replace failed parts under warranty. Much like choosing a lawyer or an accountant, you should approach the choice of an HVAC contractor carefully.

   Approach your selection of an HVAC contractor the same way you would hire an employee — interview several, get references, and decide slowly. Probably the best way to start is to call friends that live in your town, and ask them who they would recommend. Small businesses (such as the typical HVAC company) live and die by word-of-mouth referral — if a contractor knows that one of their current clients referred them to you, they will work harder to make you happy.

If you can’t find enough contractors through word-of-mouth, consider working with a company that maintains a network of HVAC contractors. (For example, FurnaceCompare.com happily recommends hiring contractors through servicemagic. ServiceMagic provides a free, no-obligation service to match people with pre-screened contractors. After the contractor completes a job, ServiceMagic emails the customer to request feedback on the contractor. They then use that feedback to select which contractors to refer for future jobs.

   Make sure to ask your contractor to show you a license and proof of insurance. Ask if they will perform a load calculation to determine how large of heat pumps to install. If they suggest that they have a shortcut for determining the correct heat pump size, keep looking! In addition, check with the Better Business Bureau to see if anyone has filed a complaint about their company. Ask for references from three previous customers — and then call to followup with those references. Make sure that there’s a good fit between personalities — you want to be sure that you feel comfortable asking questions. While price is usually an important consideration, make sure that the low-cost contractor you hire has an excellent reputation!

 

 

from:china-heat-pump|air conditioner

Mar 2, 2010 at 07:00 o\clock

Air source heat pump example

by: zhonglv   Keywords: Air, source, heat, pump

European – Air source heat pump
Summary
The purpose of the project was to build a low energy and low cost prefabricated house without compromising the comfort. Due to the overall reduced energy consumption in low energy houses the proportion of the heat required for DHW increases from 30% to 40%. This sets new requirements for a heating system. In this residence there are two air source heat pumps : one for heating (from October to April) and the other for DHW (DHW; all year round).
  MINERGIE-single-family house in Schötz (NTH4).
The former uses outdoor air and the latter indoor exhaust air as its heat source. The SPF of the 4.6 kW heat pump for space heating is 3.0. If auxiliaries such as fans for heat recovery and standby losses of the water heater are considered as well the SPF drops to 2.0.
This case study is based on information from (NTH4). For ordering information see below.

 

Building and design values

Building type: Single-family house
Location:
Year of construction: 1998
Number of storeys: 2
Heated floor area (m2): 155
% of total floor area (%): No data (basement unheated)
Design outdoor temperature (ºC) Heating: -9 Cooling: -
Design indoor temperature (ºC) Heating: 20 Cooling: -
Degree days Heating: 3 294 Cooling: -
Base temperature for degree days (ºC) Heating: 12/20 Cooling: -

 

Heating and cooling (NTH4)

Application: Space heating, DHW
Heat pump type(s): Air to water heat pump (space heating), separate air-to-water heat pump water heater (DHW)
Heat pump installed capacity (kW) Heating: 4.6
A-7/W351
DHW: 1.0
A20/W50
Refrigerant: R290 and R134a (DHW)
Heat source Outdoor air (space heating), exhaust air (DHW) from two bathrooms, toilet, kitchen, laundry room
Details: Circulation pump 35 W (heat distribution)
Distribution system(s): Floor heating elements/water without thermostatic valves
Supply and return temperature (ºC) Heating: 35/302 Cooling: -
Auxiliary system: None
Heat pump design:
  • Heating demand of the house (20ºC, air change rate=0.3/h) according to a SIA3 model was calculated as 181 MJ/m2a. The actual amount used was higher at 242 MJ/m2a (23ºC) because of higher effective averag e room temperature, higher air change rate etc.
  • DHW (57 l/person/day, 50ºC) 12 months a year, space heating in winter period.
  • The return temperature control is dependent on outdoor temperature. Utility restrictions do not allow heat pump operation at 2-4, 10-12 and 17-19 o??clock.
Supplementary system: None
Heat pump system completion date: 1998

1 A-7/W35: Air -7ºC, water 35ºC. etc.
2 With a utility cutoff period of 6 hours; continuous operation would allow 30/25
3 Huber Energietechnik, Ingenieur- und Planungb??ro SIA; model no. 380/1

 

Performance (NTH4)

Energy for heating, DHW and ventilation Heat pump Aux. heating system Auxiliaries 4
Energy input (kWh/year): 4 859 - 548
Energy output (kWh/year)1: 13 801 - 2745
Energy cost (CHF/year)2: 535.66 - -
Cost tariff (CHF/kWh)3: 0.16/0.10 - -

1 Measured data
2 Calculated from values during low (38%) and high (62%) tariff period and basic annual (CHF 57.60) cost. Costs include auxiliaries!
3 High/low
4 Auxiliaries include circulation pump for heat distribution and fan during off-time of heat pump water heater
5 Assumption: 50% of auxiliaries energy input can be used for space and hot water heating

Coefficient of performance (COP)
Heating: 4.0 and 2.5 (space heating)
Test conditions: A7/W35 and A-7/W35
Cooling: -
Test conditions: -
Heat pump cost breakdown
Heat pump only (CHF): 9 850 (space heating) and 4 660 (DHW)
Installation (CHF): 4 000
Capital cost (excluding heat pump) (CHF): 17 175
Maintenance (CHF/year): 150

 

Comparison of annual costs
Figure 3: Comparison of annual cost of various systems for heating, ventilation and DHW. Options 1-6:

  1. Oil-fired boiler (16 kW), electric backup for DHW; balanced ventilation with heat recovery

  2. Air-to-water heat pump (4.6 kWth) and exhaust-air heat pump water heater

  3. Gas-fired boiler (13 kW), electric backup for DHW; balanced ventilation with heat recovery

  4. Wood-fired burner, electric boiler for DHW, balanced ventilation with heat recovery

  5. Integrated heat pump system for space heating, DHW, ventilation and heat recovery, back-up electric boiler (for application in ??passive house??).

  6. Ground-source heat pump (4.9 kWth), electric backup for DHW, balanced ventilation with heat recovery

 

Operational experience and other comments
Schematic of the heat pump system (NTH4). This project has demonstrated that a low energy, low cost element (prefabricated) house can be built without compromising the comfort. Similar 2-storey houses exist on this housing estate, which is about 508 m above the sea level.
In low energy houses the overall reduced energy consumption significantly increases the proportion of the heat required for DHW, from 30% to 40%. This sets new requirements for a heating system.
Some heat pump related improvement ideas were raised after completing the monitoring programme:

  • The heat pump capacity should be lower than required rather than higher than required.

  • Low temperature distribution systems (Tsup>25?ラ are self-regulating

  • Mixing or thermostatic valves are not necessary.

  • Overheating in fall and spring may be a problem. Shading devices are essential.

  • The equipment should be in heated space.

It is estimated that the heat pump can be used for 15 years and the pipes etc. for 30 years.

 

 

from:china-heat-pump|heat pump