Tuesday, June 15, 2010

Heat Pump Selection: Homeowner's Guide

If you have already started your hunt for equipment you know that there are a lot of options for geothermal heat pumps. What follows are some things to think about to help narrow your search.

There are plenty of good manufacturers and heat pump brands out there, so rather than list every reputable manufacturer, we’ll give you a couple of guidelines to follow when looking for a ground source heat pump (GSHP) brand.

A little known fact about geothermal heat pumps — many GSHP manufacturers use the same or similar mechanical components. This doesn't mean that all are created equal but the wearable parts are usually of comparable quality across the major brands. The primary differences will be the control system and the geometry/effectiveness of the heat exchanger. So, the decision of one brand over another will usually come down to a few key parameters like price, availability, lead time and warranty.

Price

Price is of course of primary concern to any responsible consumer and for heat pumps the advice is the same as it is for any major purchase: The most expensive isn’t necessarily the best and the least expensive isn’t necessarily the worst. Establish your budget and look for options that meet your system requirements within that framework.

Availability

In today’s digital age, it is very common to do most of your research online, make your decision and then purchase. The problem is that not all manufacturers have distributors in all areas. This will make purchasing, as well as installing a geothermal heat pump more difficult and more expensive. In other words, start by finding what is available to you in your area, then research which of those will work best.

Lead Time

Another factor to watch for is product lead time. It is common to see lead times on GSHPs of anywhere from 2-10 weeks, depending on the manufacturer. Always remember that it is never too early to start planning your project. Ordering your equipment sooner rather than later can mitigate problems caused by delays in the supply chain.

Warranties

Often, the warranty is an after-thought, yet becomes really important if you have a problem. Standard warranties can be as short as one year including parts and labor but can also cover individual components for 5 or 10 or 15 years. It is fairly uncommon to have mechanical problems with GSHPs, especially the factory built portion. If problems do arise, it’s most common for the issue to present itself during the first year of operation. Either way, you should read and understand the terms of the warranty before you purchase so that if a problem does arise, you know you are well protected.

In addition to the manufacturer’s warranty there are also installer warranties/guarantees. We will talk more about them in a later article about choosing a qualified and reputable installer. Our next article will go beyond a homeowner's considerations and get into the numbers of sizing and selecting equipment for system designers.

Wednesday, June 2, 2010

Project Highlight: Construction Details

Instead of just showing you the highlights of the installation of the GSHP system we are installing for our new facility, we decided to take things a step further and turn this into what we are calling a Project Highlight. As the project progresses we will go through and provide you with the full details of the decisions we have made with regard to the project and the reasoning for those decisions. Our hope is that this will shed some light on the areas of design that newer designers are a little uncomfortable with and maybe remind some of the more experienced designers about a nuance or two.

The first installment of the Project Highlight is an introduction to the project with the construction properties of the facility as well as the resulting building load calculations. The 127.5’x60’ slab-on-grade style facility has 90’ of the total length with 20’ side walls with a 24’ peak and 37.5’ of building length with 12’ side walls and a 16’ peak. Other construction details are as follows:

  • Metal sheathed walls with 2” x 6” framing and R-19 batt. insulation
  • A metal sloped roof/ceiling over a wood frame with R-38 batt. Insulation
  • Slab-on-grade floor, heavy dry soil, 2” foam edge insulation 3’ down, tile floor
  • Low-e windows with a U-value of 0.410
  • Doors will be metal with a fiberglass core
  • Occupancy levels of 10 people and 2 appliances

Our home offices are located in Elkton, SD. Elkton is a small town roughly one mile West of the South Dakota-Minnesota state line, and 15 miles East of Brookings, SD. The weather location we chose to calculate the building loads is Brookings, SD. The 99% heating design percentage for Brookings, SD is -11°F, while the 1% cooling design temperature is 85°F. These are the temperature points that the peak heating and cooling loads are based on.

Now that all of the construction details are given, we can determine the peak building loads in heating and cooling using the ACCA manual-J load calculation procedure. The peak loads were determined to be 124,081 Btu/hr and 42,309 respectively.